Power amplifiers based on combining two power stages where one supplies the bulk of the load power and the other ensures high output signal quality are discussed. The entire class of such combinations is described, with particular attention given to a unique parallel topology. Experimental and theoretical results show that this topology has high performance without large efficiency or hardware penalties.

[2] F. C. Zach, K. H. Kaiser, J. W. Kolar, and F. J. Haselsteiner, "New lossless turn-on and turn-off (snubber) networks for inverters, including circuits for blocking voltage limitation," IEEE Transactions on Power Electronics, vol. PE-1, no. 2, pp. 65-75, 1986.

The authors describe lossless turn-on and turn-off circuits for transistorized pulsewidth modulated inverters. In particular, the turn-off circuits discussed show a highly reduced parts count compared to circuits known from the literature. The turn-on circuits use energy recovery. Also, due to special circuit design, the voltage across the power transistor is strictly limited.

[3] G. C. Verghese, M. E. Elbuluk, and J. G. Kassakian, "General approach to sampled-data modeling for power electronic circuits," IEEE Transactions on Power Electronics, vol. PE-1, no. 2, pp. 76-89, 1986.

A general sampled-data representation of the dynamics of arbitrary power electronic circuits is proposed to unify existing approaches. It leads, via compact and powerful notation, to disciplined modeling and straightforward derivation of small-signal models that describe perturbations about a nominal cyclic steady state. Its usefulness is illustrated by considering the representation and analysis of a class of symmetries in circuit operation. The results of the application of this methodology to modeling the small-signal dynamics of a series resonant converter are described. The results correlate well with simulation results obtained on the Massachusetts Institute of Technology's parity simulator. The small-signal model is obtained in a completely routine way, starting from a general formulation and working down to the actual circuit; this contrasts with circuit-specific analyses. The automatability of this procedure is also discussed, and it is pointed out that the key ingredients for automatic generation of dynamic models from a circuit specification are now available.

[4] M. Groetzbach and R. von Lutz, "Unified modeling of rectifier-controlled dc-power supplies," IEEE Transactions on Power Electronics, vol. PE-1, no. 2, pp. 90-100, 1986.

The analysis of dc-dc converters in the discontinuous operation mode with voltage communication is extended to the analysis of line-commutated converters based on a piecewise-linear description. With the line-commutated converters as system-dependent pulsewidths, the overlap angles appear and are computed in a manner analogous to the current-flow duration and the reloading time, respectively. This leads to a unified state-space modeling of dc-dc and ac-dc converters by which the steady-state and the dynamic small-signal behavior can be evaluated directly. If the piecewise-defined system equations are integrated numerically, a rather generalized analysis of power converters is found if the structure of switched systems is taken into account. As an illustrative example, a voltage-commutated dc-dc converter with a nonlinear dc inductance is studied.

[5] D. Pei and P. O. Lauritzen, "Computer model of magnetic saturation and hysteresis for use on spice2," IEEE Transactions on Power Electronics, vol. PE-1, no. 2, pp. 101-110, 1986.

Magnetic saturation and hysteresis are simulated on SPICE2 using a model containing two nonlinear controlled sources. The model is applied to inductors and transformers made from a variety of core materials, and procedures are given for determining the model parameters directly from magnetic core catalog data. Four examples of circuit applications are given: a saturating instrumentation transformer, a saturating snubber inductor, a ferroresonant regulator transformer, and a Royer saturation oscillator. These particular applications were selected because saturation of an inductor or transformer is fundamental to each circuit's operation.

[6] R. Redl, B. Molnar, and N. O. Sokal, "Class e resonant regulated dc/dc power converters: Analysis of operations, and experimental results at 1. 5 mhz," IEEE Transactions on Power Electronics, vol. PE-1, no. 2, pp. 111-120, 1986.

Analysis, design considerations, and experimental results at 1. 5 MHz are presented for a resonant high-frequency Class E dc/dc converter. The power switch operates with very low switching stress and switching power loss even if the switch transition times are an appreciable fraction of the period. The analysis gives the permissible area of the equivalent load impedance for lossless operation, presents a model for regulation by narrowband frequency control, and characterizes the output full-wave rectifier. Experimental data from a 1. 5-MHz 40-W converter verify the results of the theoretical analysis. The measured efficiency was 85%.

[7] R. Redl, B. Molnar, and N. O. Sokal, "Small-signal dynamic analysis of regulated class e dc/dc converters," IEEE Transactions on Power Electronics, vol. PE-1, no. 2, pp. 121-128, 1986.

The authors give static and dynamic characterization of the Class E dc/dc converter cell. The theory agrees well with experimental measurements on a 40-W, 1. 5-MHz demonstrator unit. It is felt that this report will serve as a guideline for predicting circuit operation and for designing practical converters.

[8] M. Shoyama and K. Harada, "Dynamic characteristics of the push-pull dc to dc converter," IEEE Transactions on Power Electronics, vol. PE-1, no. 1, pp. 3-8, 1986.

The dynamic characteristics of the push-pull dc to dc converter are analyzed both theoretically and experimentally for the modes of operation which are caused by the interaction between the magnetizing current of the transformer and that of the reactor. Of the six modes of operation, four are of the first-order system. In two of the four, the instantaneous reactor current does not fall to zero at any point in the switching cycle.

[9] J. B. Klaassens, "Dc-to-ac series-resonant converter system with high internal frequency generating synthesized waveforms for multikilowatt power levels," IEEE Transactions on Power Electronics, vol. PE-1, no. 1, pp. 9-20, 1986.

A new method of power pulse modulation with internal frequencies of tens of kHz that is suitable for multikilowatt power levels is applied to a series-resonant converter system for generating synthesized unipolar and bipolar waveforms. The high pulse frequency allows the principle of modulation and demodulation to be applied for fast system response and output waveforms with low distortion and prevents excessive stresses on components. Natural current communication of the thyristors is obtained by use of a series-resonant circuit for power transfer and control. Test results of a 4-kW thyristor converter system generating sinusoidal and nonsinusoidal waveforms independently of the load characteristics demonstrate the significant aspects for this class of power conversion. The material presented indicates the capability of the system to avoid excessive component stresses as well as the possibilities for fast-acting four-quadrant dc-to-dc, single-phase or polyphase dc-to-ac and ac-to-ac converter systems.

[10] S. S. Kelkar and F. C. Y. Lee, "Fast time domain digital simulation technique for power converters: Application to a buck converter with feedforward compensation," IEEE Transactions on Power Electronics, vol. PE-1, no. 1, pp. 21-31, 1986.

Small-signal analysis was performed earlier (1982) to demonstrate the marked improvement of the dynamic properties and stability margins of a switching regulator using a novel feedforward input filter compensation scheme. A large-signal nonlinear recurrent time-domain model is presented here for the converter to analyze the transient response due to a step input change with and without the presence of the proposed feedforward loop. The results are verified with experimental data.

[11] R. E. Kapustka, J. R. Bush, Jr., J. R. Graves, and J. R. Lanier, Jr., "Programmable transformer coupled converter for high-power space applications," IEEE Transactions on Power Electronics, vol. PE-1, no. 1, pp. 32-38, 1986.

A programmable transformer coupled converter (PTCC) is being developed by NASA/Marshall Space Flight Center for application in future large space power systems. The PTCC uses an internal microprocessor to control the output characteristics of its three Cuk integrated magnetics type power stages, which have a combined capability of 5. 4 kW (30 V at 180 A). Details of design tradeoffs and test results are presented.

[12] G. Perica, "Elimination of leakage effects related to the use of windings with fractions of turns," IEEE Transactions on Power Electronics, vol. PE-1, no. 1, pp. 39-47, 1986.

Obtaining exact output voltages from transformers is a difficult task due to discrete turn ratios. This becomes even more difficult in modern switching power supplies operating above 100 kHz because the number of turns per winding is reduced. For multichannel applications different methods of postregulation are used, resulting in increased power dissipation and power supply cost. A new method of dealing with the problem has been developed which offers a higher degree of flexibility. This technique allows fractions of turns to be used and maintains low leakage inductances. A theoretical analysis of leakage effects related to fractional turn windings has been carried out, and tests on an experimental transformer have been performed.

[13] B. H. Cho and F. C. Y. Lee, "Measurement of loop gain with the digital modulator," IEEE Transactions on Power Electronics, vol. PE-1, no. 1, pp. 55-62, 1986.

A loop gain measurement technique for switching regulators using a digital modulator is introduced. While the conventional technique injects and measures the analog signals, the proposed digital modulator injects a digital perturbation and measures the resultant duty cycle modulation. Since the duty cycle signal, derived from all feedback loops, provides the ultimate control of a switching regulator, the loop gain defined at the duty cycle modulator is unique. With the digital modulator, this loop gain can be measured even with a switching regulator using the current injected control. Furthermore, this new technique overcomes the false measurement problems found in the conventional technique when the feedback signal at the point where the loop gain is measured has a pulsating nature.

[14] G. Eggers, "Fast switches in linear networks," IEEE Transactions on Power Electronics, vol. PE-1, no. 3, pp. 129-140, 1986.

The behavior of fast switches in linear networks is investigated as an application of the finite Laplace transformation. In order to demonstrate the usefulness of this technique, a nonideal boost power stage is modeled. The related crucial steps reside in establishing finite Laplace transforms of the pulsating parameters and their subsequent simplification by applying conditions imposed by the filtering networks. This leads to the result that pulsating parameters can be represented mathematically as Dirac pulses. It is in essence the content of these Dirac pulses which form the amplitude of the envelope of the filter output signal in the time domain. The effect of rise and fall time, reverse recovery time, etc., on the modulated switch output was thoroughly studied.

[15] G. Gierse and W. Schuermann, "Microprocessor control for two magnetically coupled three-phase pwm inverters," IEEE Transactions on Power Electronics, vol. PE-1, no. 3, pp. 141-147, 1986.

The requirements on the control set for two pulse-width-modulation (PWM) inverters coupled by a three-phase harmonic canceling reactor are described. Its method of operation, which is based on a microprocessor Intel 8086 is explained. The input information is a reference space vector which represents the required motor voltages. It is shown how the six respective inverter-output potentials are calculated in a very short time based on this reference vector. One free-running mode for low frequencies and special pulse sequences which are synchronized with the stator frequency is realized. The control device was successfully tested on a 120-kW double inverter experimental installation. One asynchronous and eight synchronous pulse-sequences were implemented. The reference space vector was derived from an analog asynchronous machine control.

[16] A. H. Weinberg and J. Schreuders, "High-power high-voltage dc-dc converter for space applications," IEEE Transactions on Power Electronics, vol. PE-1, no. 3, pp. 148-160, 1986.

The design details of a modular dc-dc converter used to power the main anode supply of a mercury-iron motor are presented. This motor, the RIT-35, is used as the propulsion unit of a future Asteroid Gravity Optical and Radar Analysis (AGORA) mission. The design that was selected to cope with the high-voltage high-power conversion for space applications is shown. A galvanically isolated FET drive circuit is used that provides a true 0-100% duty cycle operation with negative OFF gate-source voltage for the high-radiation environment. The converter must operate from an unregulated solar array with a voltage excursion of from 150 V at beginning-of-mission to 240 V at end-of-mission. Also highlighted are design features to reduce internal electromagnetic interference by the use of printed-circuit-board power buses and by careful design of the internal grounding. 3 refs.

[17] A. S. Kislovski, "Contribution to steady-state modeling of half-bridge series-resonant power cells," IEEE Transactions on Power Electronics, vol. PE-1, no. 3, pp. 161-166, 1986.

A power conditioning cell of the series-resonant type is analyzed in the continuous conduction mode below the resonant frequency. The injected-absorbed current method is used to establish relationships between different cell parameters. A numerical solution of the normalized key relation is presented as a family of easy-to-use graphs. These graphs and a design flowchart leading to the essential cell waveforms are combined into a comprehensive and straightforward approach for the analysis and design of this cell. This approach is showing remain valid for the discontinuous conduction mode if the resonant current is restricted to only two pulses of alternate polarities. In both modes the results obtained are applicable to the twin-capacitor half-bridge configuration. The graphoanalytic procedure starts from a practical initial data set and permits a direct and fast visualization of the influence of the two freely chosen parameters upon the essential cell waveforms. Optimization of design tradeoffs is substantially simplified and an informed choice of the free parameters is possible.

[18] D. M. Mitchell, "Analytical investigation of current-injected control for constant-frequency switching regulators," IEEE Transactions on Power Electronics, vol. PE-1, no. 3, pp. 167-174, 1986.

State-space averaging and linearization are applied to current-injected, constant-frequency switching regulators, resulting in a generalized two-loop system representation. The boost regulator is examined in detail to show that, as a theoretical goal, wide-bandwidth, first-order behavior can be achieved with no right-half-plane zeros. It is concluded that it is questionable that such performance can be achieved in practice. This is particularly so for push-pull topologies, since the gain at half the switching frequency may be too high and an excessive imbalance may result. Actual performance may be limited by switching frequency interference considerations.

[19] K. Harada, H. Sakamoto, and M. Shoyama, "On the high-speed turn-off of a power transistor by a small saturable core," IEEE Transactions on Power Electronics, vol. PE-1, no. 3, pp. 175-180, 1986.

It is shown that a dc-dc converter operating with a switching frequency in the megahertz region is possible using a bipolar transistor as the main switch. The circuit uses current feedback with a small saturable core in the base drive circuit. When the main switching transistor is turned off, the excess carriers in the base region are discharged quickly by the large reverse base current. This brings about a shortened turn-off time with little dissipation in the base drive circuit. The turn-off mechanism is analyzed with equivalent circuits. The approximate expressions for the storage time and the fall time are derived and confirmed by experiments. An efficiency of 78% was obtained with the switching frequency of 1. 5 MHz in the experimental circuit used to verify the analysis.

[20] R. Redl and N. O. Sokal, "Near-optimum dynamic regulation of dc-dc converters using feed-forward of output current and input voltage with current-mode control," IEEE Transactions on Power Electronics, vol. PE-1, no. 3, pp. 181-192, 1986.

Near-optimum dynamic regulation of a dc-dc converter is obtained by adding feedforward of output current and input voltage to a current-mode controller. This results in: (a) near-zero output impedance and audio susceptibility from dc to nearly the switching frequency; (b) greatly reduced magnitude, duration, and energy content of the output-voltage transient after a transient change of output current or input voltage; and (c) smaller size and lower cost for the output filter capacitor. Feedforward is applicable to both forward and flyback converter types and to all types of current-mode control. The cost of feedforward for a forward-type converter is a low-power resistor and a current sensor; a flyback-type converter needs an additional analog multiplier-divider integrated circuit. A description is given of the control loop; conditions to achieve extremely good transient response; calculation of the peak deviation of the output voltage for a step load change; practical methods for current feedforward; and experimental results. The theoretical predictions are in excellent agreement with the experimental results.

[21] G. Luetteke and H. C. Raets, "High voltage high frequency class-e converter suitable for miniaturization," IEEE Transactions on Power Electronics, vol. PE-1, no. 4, pp. 193-199, 1986.

A 120-V mains-driven class-E converter is presented for use as an electronic ballast for a 15-W fluorescent lamp. The key element of the circuit is a cascoded bipolar metal-oxide semiconductor (BiMOS) switch which ensures high-voltage and high-frequency capability. In spite of the high switching frequency of 450 kHz an excellent efficiency of 91% was achieved. It is concluded that this breadboard study demonstrates the feasibility of fluorescent lamp miniaturization.

[22] Y. Kuroe, H. Haneda, and T. Maruhashi, "New computer-aided method of distortion sensitivity-analysis and its elimination scheme for power electronic circuits," IEEE Transactions on Power Electronics, vol. PE-1, no. 4, pp. 200-209, 1986.

Efficient computer-aided methods are proposed to evaluate the sensitivities of power electronic circuit parameters to distortion and to eliminate undesirable harmonics from these circuits. The adjoint network approach is used for calculating the parameter sensitivities, and an optimal filter design algorithm is proposed to reduce and eliminate the distortion of current and voltage waveforms. The algorithms are very easy to implement using the existing package ANASP, a general-purpose steady-state analysis program for power electronic circuits. Numerical results are provided for an illustrative example.

[23] H. Kubota, K. Matsuse, and J.-H. Ree, "Analysis of new current source gto inverter-fed induction motor drive," IEEE Transactions on Power Electronics, vol. PE-1, no. 4, pp. 210-214, 1986.

An improved current source gate turn-off thyristor (GTO) inverter is analyzed with an induction motor load. The GTO incorporates an improved energy rebound circuit (for reactive power control) that is composed of a diode bridge, a capacitor, and a discharging circuit. The new design is compared to a conventional autosequentially commutated current source inverter (ASCI). It is found that commutation period of the inverter can be widely varied by controlling the discharging period of the capacitor, and the period is related to the surge voltage (capacitor voltage). The discharge period is seen to be influenced by the inverter frequency, motor slip, and current.

[24] S. Okada, T. Tanaka, and H. Kashara, "New high frequency cycloconverter," IEEE Transactions on Power Electronics, vol. PE-1, no. 4, pp. 215-222, 1986.

An ac-to-ac frequency converter is introduced which uses three pairs of back-to-back thyristors, and converts a three-phase power frequency to a single-phase higher frequency. In the system presented, each pulse flows through either one switch or two parallel switches; this provides good efficiency with the advantage of a small parts count. Features inherent in this type of converter such as stable operation, high power factor, and low harmonics are maintained. Two equivalent circuits (each as viewed from power source and load) were derived. Their applicabilities were verified by comparing characteristics obtained from the equivalent circuit with those obtained from simulation of the original circuit. It was shown that the proposed converter has good input power factor and input harmonics for varied load conditions.

[25] K. D. T. Ngo, "Low frequency characterization of pwm converters," IEEE Transactions on Power Electronics, vol. PE-1, no. 4, pp. 223-230, 1986.

The describing state-space equation is discussed as a technique to characterize low-frequency behavior of pulse-width modulation (PWM) dc and ac converters, inverters, rectifiers, and cycloconverters. The two-terminal basic switching elements (or throws) in a converter are grouped into multiple-throw switches and assigned switching functions. Switching (state-space) equations are obtained by using switching functions and inspecting the topology, without having to analyze all switched circuits one by one. Describing equations result from switching equations when switching functions are replaced by the respective duty ratios, and exact variables (excitations, states, and outputs) are replaced by respective low-frequency components. Describing equations of ac converters are transformed to rotating coordinates so that they are time-invariant (as those of dc converters).

[26] J. D. Law and T. A. Lipo, "Single phase induction motor voltage controller with improved performance," IEEE Transactions on Power Electronics, vol. PE-1, no. 4, pp. 240-247, 1986.

An improved power-factor control scheme is presented for a single-phase permanent split-capacitor induction motor. The scheme is accomplished by dynamically switching the winding configuration. Laboratory data for a voltage controller that was thus enhanced indicates a greatly improved efficiency for the modified voltage controller over a conventional voltage controller below one-quarter load. Circuit details of the thyristor phaseback voltage controller used in obtaining the laboratory data are given. Duty cycle curves are presented for the tested machine.

[27] M. F. Schlecht, "Harmonic-free utility/dc power conditioning interfaces," IEEE Transactions on Power Electronics, vol. PE-1, no. 4, pp. 231-239, 1986.

The typical design of a power circuit used to interface a dc system to the electric utility is such that a heavily distorted current is drawn from the utility. Since this distortion has the potential to interfere with the normal operation of the utility and its load, efforts are underway to develop power-conditioning interfaces that draw a nearly harmonic-free ac current waveform. The design of these interfaces is discussed. The salient issues of the power circuit's topology and its control are presented. Fundamental design options are compared. The important points in this comparison are: (1) the second-harmonic impedance that characterizes the dc system affects both the topology of the high-frequency converter and the range of operation of the interface; (2) unity power factor operation requires a simpler power circuit than does a bidirectional power flow; (3) power flow toward the dc system requires diodes for the bridge switches, while power flow toward the utility requires controllable switches; (4) a tuned resonant load-balancing filter, which is only practical with a harmonic-free interface, greatly reduces both the size and the dynamic response time of this part of the interface; and (5) open-loop control of the utility current's shape is possible with the dc current-source approach while closed-loop control is necessary for the dc voltage-source approach.

[28] N. R. Coonrod, "Transformer computer design aid for higher frequency switching power supplies," IEEE Transactions on Power Electronics, vol. PE-1, no. 4, pp. 248-256, 1986.

A method for the computer-aided design of transformers is presented that was developed for use at switching frequencies above 100 kHz. At such high frequencies, the classical method of using the saturation constraint results in an overheated transformer due to excessive core loss. In the proposed method, flux density is selected by an optimization procedure that minimizes total transformer losses. The computer is used to find the optimum value of flux density based on thermal considerations. In particular, the minimum-size transformer that still exhibits a satisfactory temperature rise is determined. The transformer design aid can be used for current or voltage fed pulsewidth-modulated power supplies in either the bridge or push-pull configuration, using toroidal ferrite cores. The design procedure, including key equations, is presented in enough detail so that it can be adapted for use with other switching power supply topologies and core geometries. Emphasis is placed on the algorithm used in the transformer design procedure.

[29] K. Harada, H. Sakamoto, and M. Shoyama, "On the effective turn-off of gto by a small saturable core," IEEE Transactions on Power Electronics, vol. PE-2, no. 1, pp. 20-27, 1987.

A new turn-off circuit for gate-turn-off (GTO) which is simple and of low energy consumption is presented. The principle is based on the resonance between saturating inductance of the magnetic core and the parasitic capacitance included in GTO. Analytical as well as experimental results are presented.

[30] C. F. Wheatley, Jr. and H. R. Ronan, Jr., "Switching waveforms of the l**2fet: A 5-v gate-drive power mosfet," IEEE Transactions on Power Electronics, vol. PE-2, no. 2, pp. 81-89, 1987.

The switching waveforms of a newly announced series of power MOSFET devices called logic-level FETs (L**2FETs) and featuring a 5-V gate drive are presented and contrasted with those of the more conventional 10-V gate-drive devices. A novel method of characterizing MOSFET switching performance is discussed in which the MOSFET is treated as a vertical JFET driven in cascode from a low-voltage lateral MOS. The two-to-one advantage in rise and fall time and the four-to-one reduction in switching dynamic V//(//s//a//t//) dissipation with constant drive power of the L**2FET over the 10-V MOSFET are demonstrated and discussed.

[31] Y. Hayashi, T. Suzuki, S. Ishibashi, and T. Sueoka, "Consideration on turn-off failure of gto with amplifying gate," IEEE Transactions on Power Electronics, vol. PE-2, no. 2, pp. 90-97, 1987.

Using the high-power buried-gate GTOs of various n-base carrier lifetimes, the turn-off failure phenomena peculiar to the amplifying gate (AG) GTO are investigated, under the conditions of short on-duration (30-200 mu s) and lagging current operation. From the results of this investigation, it was found that there are three kinds of AG failure mode: the off-bias voltage for the AG is insufficient to turnoff and the AG current; the 'miss-gate current' flows before the turn-off of the AG is completed; and the miss-gate current exceeds the sensitivity of the AG. As a result, the factors causing the AG failure and the desirable driving method are clarified.

[32] D. J. Shortt, W. T. Michael, R. L. Avant, and R. E. Palma, "600-w four-stage phase-shifted-parallel dc-to-dc converter," IEEE Transactions on Power Electronics, vol. PE-2, no. 2, pp. 101-108, 1987.

An unconventional switched-mode power supply (SMPS) architecture, developed as four 150-W buck-boost or flyback-type switching stages operated in phase-shifted parallel (PSP), is introduced. The flybacks are operated in the continuous mode with intersecting conduction on both input and output sides; they are switched in cyclic sequence with one-fourth of a switching period following turn-on of one stage before turn-on of the next stage. PSP operation provides substantial improvements in intermediate power level SMPS for spacecraft applications.

[33] G. B. Yundt, "Nonlinear compensation of self-oscillating switching regulators," IEEE Transactions on Power Electronics, vol. PE-2, no. 1, pp. 28-35, 1987.

The performance of self-oscillating (bang-bang) switching regulators is improved with nonlinear loop compensation. Three major results are presented: (1) increased output regulation at mid to low frequencies without degrading transient response; (2) a simple method to maintain good control in the discontinuous conduction region; and (3) simple analytical results predicting behavior for common nonidealities.

[34] M. M. Jovanovic, K.-H. Liu, R. Oruganti, and F. C. Y. Lee, "State-plane analysis of quasi-resonant converters," IEEE Transactions on Power Electronics, vol. PE-2, no. 1, pp. 36-44, 1987.

A comprehensive analysis of the high-frequency quasi-resonant buck converter is presented using the graphical state-plane technique. The analysis has revealed, for the first time, the presence of several unfamiliar modes of operation. The voltage-conversion ratio and boundary-switching frequency for each mode are derived. The existence of various operating modes are verified experimentally.

[35] D. M. Divan, "Design considerations for very high frequency resonant mode dc/dc converters," IEEE Transactions on Power Electronics, vol. PE-2, no. 1, pp. 45-54, 1987.

Conventional resonant converter circuits are not optimized for high-frequency operation. A new resonant-mode dc/dc converter topology is presented that exhibits desirable characteristics including zero switching losses, elimination of snubbers, simple control strategy, and circuit operation that is insensitive to parasitics such as diode reverse recovery. Analysis and design techniques are discussed in detail and are experimentally verified with a 150-W prototype converter operating in the frequency range of 500 kHz-1 MHz.

[36] M. Ilic-Spong, T. J. E. Miller, S. R. MacMinn, and J. S. Thorp, "Instantaneous torque control of electric motor drives," IEEE Transactions on Power Electronics, vol. PE-2, no. 1, pp. 55-61, 1987.

Some of the fundamental principles of instantaneous torque control are developed for the switched reluctance motor. This motor is used as an example because, like the brushless dc permanent-magnet motor with concentrated windings, it has the potential for rapid response, but it can have appreciable torque ripple with unfavorable firing angles. A reference frame transformation that would eliminate the rotor position from the voltage and torque equations is not known for either of these machines. This opens up a number of interesting questions as to the generality of instantaneous torque control algorithms, and whether they can be incorporated into the general or unified theory of electrical machines.

[37] K.-H. Liu, R. Oruganti, and F. C. Y. Lee, "Quasi - resonant converters - topologies and characteristics," IEEE Transactions on Power Electronics, vol. PE-2, no. 1, pp. 62-71, 1987.

In designing switching dc-dc converters, the effort to increase operating frequency to reduce weight, size, and cost of magnetic and filter elements is constantly hampered by higher switching stresses and switching losses. To overcome these obstacles, the concept of the resonant switch is proposed. By incorporating additional inductor and capacitor elements to shape the semiconductor switch's current waveform, a zero-current switching property can be realized. Based on the resonant switch technique, a new host of quasi-resonant converter circuits have been derived, which can be operated in the megahertz range.

[38] J. H. Rockot, "Losses in high-power bipolar transistors," IEEE Transactions on Power Electronics, vol. PE-2, no. 1, pp. 72-80, 1987.

The calculation of power losses in high-power bipolar transistors is examined for several of the commonly encountered types of power circuits. The magnitude of switching and conduction losses is dependent on the type of circuit in which they are used, the type of load, switching frequency, and characteristics of the transistor itself. Curves, based on computer simulation and mathematical analysis, are presented to aid in the calculation of these losses. Parameters taken into account are dynamic saturation voltage, load power factor, effect of snubbers, and recovery characteristics of circuit associated diodes.

[39] M. M. Jovanovic and F. C. Y. Lee, "Design considerations for paralleling bipolar transistors," IEEE Transactions on Power Electronics, vol. PE-2, no. 4, pp. 328-336, 1987.

A simple design procedure for direct paralleling of bipolar junction transistors (BJTs) is proposed. It is based on the matching or transfer characteristics (I//c versus V//C//E) at a low collector voltage. The design procedure further addresses the base and collector circuit's layout requirements, optimal base-driven conditions, and thermal design requirements for reliable and efficient operation of BJTs in parallel. The influence of a snubber circuit is also discussed. The procedure is verified experimentally by performing dynamic and reverse-bias safe operating area (RBSOA) testings.

[40] A. Bellini, A. De Santis, G. Figalli, and G. Ulivi, "Application of pulse ratio modulation to fixed-frequency sinusoidal tracking inverters," IEEE Transactions on Power Electronics, vol. PE-2, no. 4, pp. 337-342, 1987.

The application of pulse ratio modulation techniques in the field of fixed-frequency inverters with sinusoidal output waveforms is discussed. In particular, the criteria for choosing the parameters of the output filter and of the compensation network are analyzed, and a comparison is effected between the results obtained by using either the aforementioned modulation technique or a fixed-frequency pulsewidth modulation technique. The comparison, effected by simulation, also takes into account a nonlinear load, and shows that the use of the pulse ratio modulation technique allows a remarkable reduction of the inverter supply overvoltage necessary to use tracking control techniques with high modulation frequencies. The results obtained by simulation have been confirmed by a prototype.

[41] C.-C. Liu, K.-H. Ding, J. R. Young, and J. F. Beutler, "Systematic method for the stability analysis of multiple-output converters," IEEE Transactions on Power Electronics, vol. PE-2, no. 4, pp. 343-353, 1987.

The dynamics of multiple-output dc-dc converters are discussed. A multi-input-multioutput (MIMO) feedback system model incorporating effects of the output fluctuation is derived for the converter. Based on system-theoretic tools, a set of stability conditions is obtained for the MIMO model; the result is used to formulate a stable margin. A practical five-output converter was selected for illustration of the proposed analytical tool. The effects of the input filter and coupled inductor on system stability margin are investigated.

[42] H. P. Lips, G. H. K. Thiele, N.-H. Huynh, and P.-E. Vohl, "Design and testing of thyristor valves for the hvdc back-to-back tie chateauguay," IEEE Transactions on Power Electronics, vol. PE-2, no. 4, pp. 354-361, 1987.

A 1000-MW back-to-back link between Hydro-Quebec and the New York Power Authority, implemented at the Chateauguay substation, is considered. Some of the more important requirements specified by Hydro-Quebec are presented. The resulting design optimization is discussed and special features of the design are pointed out. Testing requirements as compared to International Electrotechnical Commission (IEC) Standards are discussed and results presented.

[43] S. Roccucci and L. Turrini, "Ac power distribution for satellites," IEEE Transactions on Power Electronics, vol. PE-2, no. 2, pp. 125-135, 1987.

A dc to ac converter for ac power distribution on-board spacecraft is described. A demonstration model was implemented with the following essential characteristics: input 50 Vdc plus or minus 20% and output 50 Vac, 13 kHz, 1 kW. Higher power requirements can also be satisfied by the design. The ac output has such characteristics as to be able to feed low-voltage transformer-rectifier-type power supplies, such as those used for up-converters, multipliers, intermediate frequency (IF) amplifiers, etc., as well as high-voltage power supplies used for travelling wave tubes (TWTs), Klystrons, etc. Design milestones and approaches are discussed, and significant circuit details, components used, protection techniques, and techniques to minimize electromagnetic interference (EMI) are presented. Input and output characteristics related to high-voltage and low-voltage dc loads are given.

[44] D. L. Blackburn, "Turn-off failure of power mosfet's," IEEE Transactions on Power Electronics, vol. PE-2, no. 2, pp. 136-142, 1987.

Experimental results of the failure of power MOSFETs during inductive turn-off are discussed. The electrical characteristics of these devices during failure are shown to be identical to those of a bipolar transistor undergoing second breakdown. Other comparisons of the power MOSFET failure and bipolar second breakdown are made. A nondestructive measurement system is used that allows repeated measurements of the failure characteristics as a function of various parameters to be made on a single device. It is shown that commercially available power MOSFETs do not fail as a result of dV/dt currents. Drain voltage slew rates of up to 22 V/ns were studied. Other measurements show that the drain voltage at which failure occurs decreases with temperature, and that the magnitude of the load inductance has no effect on the failure.

[45] J. L. Hudgins and W. M. Portnoy, "High di/dt pulse switching of thyristors," IEEE Transactions on Power Electronics, vol. PE-2, no. 2, pp. 143-148, 1987.

The fast-pulse-switching behavior of center-fired ring-and-dot and interdigitated thyristors was studied by switching 8 to 10 mu s, 1000 to 1600 A peak (at 800 V) pulses. Single-shot switching was performed up to 15,400 A/ mu s, and repetitive switching at 500 and 800 Hz at various di/dt levels, including 13,000 A/ mu s, for up to ten hours. No damage to the devices resulted from the single-shot switching stresses.

[46] J. L. Hudgins and W. M. Portnoy, "Gating effects on thyristor anode current di/dt," IEEE Transactions on Power Electronics, vol. PE-2, no. 2, pp. 149-153, 1987.

Triggering measurements were performed on thyristors with different gate geometries at various combinations of peak gate current, gate pulsewidth, and gate di/dt, to determine the trigger dependence of pulsed anode current di/dt. Peak gate current was varied from 4 A to 12 A, gate pulse width from 250 ns to 8 mu s, and leading edge di/dt from 23 A/ mu s to 320 A/ mu s. Only the peak gate current was found to affect pulsed anode current di/dt.

[47] R. C.-S. Wong, H. A. Owen, Jr., and T. G. Wilson, "Efficient algorithm for the time-domain simulation of regulated energy-storage dc-to-dc converters," IEEE Transactions on Power Electronics, vol. PE-2, no. 2, pp. 154-168, 1987.

An algorithm is presented for the efficient and accurate simulation of switched-mode piecewise-linear systems, a subclass of which includes regulated energy-storage dc-to-dc converters. Three key features of the algorithm that lead to significant improvements in computational efficiency and accuracy are: a state-transition-matrix table-lookup scheme to solve differential equations describing the system; a modified binary-speech strategy to obtain an initial estimate of the instant at which the system topology switches; and a quadratic extrapolation for the accurate final determination of the switching instant. The computational efficiency of a program using the algorithm is demonstrated by comparing its execution time with that of a program employing a standard fixed-step-size integration algorithm. The accuracy of the new algorithm is verified by comparing results obtained from the simulations with results obtained analytically, and by comparing data from the simulation of two different regulated converters with data measured experimentally.

[48] F. Harashima, J.-X. Xu, and H. Hashimoto, "Tracking control of robot manipulators using sliding mode," IEEE Transactions on Power Electronics, vol. PE-2, no. 2, pp. 169-176, 1987.

A methodology using the theory of variable structure systems is developed for accurate tracking control of robotic manipulators. The proposed method, based on a sliding-mode controller, produces a discontinuity control input so that the nonlinear interactions and influence caused by unknown parameter variations can be depressed whereas the resulting control law is simple and easy to apply to online computer control. The digital simulation results of a three-degree-of-freedom manipulator show the validity of accurate tracking capability and robust performance of the system with the developed control scheme.

[49] M. Stoisiek and D. Theis, "Turn-on principles of the mos-gto," IEEE Transactions on Power Electronics, vol. PE-2, no. 4, pp. 362-366, 1987.

MOS-GTOs (GTO thyristors that are turned off by the action of a MOS-gate) offer considerable advantages in turn-off behavior as compared to conventional GTOs. However, MOS-GTOs generally require one control electrode for turn-on and another control electrode for turn-off, which might be regarded as a disadvantage. It is shown that in MOS-GTOs with a p-channel cathode structure it is possible to turn the thyristor on and off by controlling just one MOS gate electrode. As a triggering current for turn-on, the MOS capacitor charging current is used.

[50] J. Rodriguez, "Simple control method for a switching rectifier with power transistors," IEEE Transactions on Power Electronics, vol. PE-2, no. 4, pp. 367-372, 1987.

A very simple control method for a high-frequency switching rectifier with power transistors is presented. The converter uses six semiconductor switches with turn-off capability to connect the three-phase source directly to the load. Each semiconductor switch is composed by two power MOSFET transistors. The control method is based on the fictitious bipolar source concept. A two-level controller with hysteresis is used to control the load current. The converter accepts power flow in both directions, does not need large storage elements, works with good power factor, and can generate output frequencies higher than the source frequency, without affecting the quality of the output current. The control and logic circuits of the rectifier are very simple, due to the high controllability of the bidirectional switches. The performance of the converter is investigated experimentally in the four-quadrant speed control of a dc machine.

[51] P. Viriya, H. Kubota, and K. Matsuse, "New pwm-controlled gto converter," IEEE Transactions on Power Electronics, vol. PE-2, no. 4, pp. 373-381, 1987.

A novel pulsewidth-modulation (PWM)-controlled GTO converter circuit is proposed. An auxiliary circuit capacitor is used to treat the commutating energy in the main circuit and to clamp the commutating impulse voltage at the desired level with the fundamental power factor of unity. An analysis of the circuit operation is verified experimentally.

[52] R. D. Middlebrook, "Topics in multiple-loop regulators and current-mode programming," IEEE Transactions on Power Electronics, vol. PE-2, no. 2, pp. 109-124, 1987.

Some general considerations about multiple-loop feedback are discussed, and it is concluded that incorporation of a current- programmed power stage into a 'new' power stage model is both justified and useful. A new circuit-oriented model of the current feedback path is derived which augments the well-known power stage canonical circuit model. The new power stage is more usefully modeled by a y-parameter model in which the current loop is not explicit. Expressions for the y parameters are given that are extensions of those previously derived. Another form of the model resembles the original canonical form for duty ratio programming, and shows that current programming effectively introduces lossless series damping that separates widely the two poles of the power stage LC filter.

[53] C. K. Chu, P. B. Spisak, and D. A. Walczak, "High-power asymmetrical thyristors," IEEE Transactions on Power Electronics, vol. PE-2, no. 2, pp. 98-100, 1987.

The power loss of fast-speed thyristors is relatively high, especially for higher blocking voltage devices. High-power asymmetrical thyristors can reduce the power loss up to 40%. The electrical characteristics of newly developed 3000-V and 4000-V high-power asymmetrical thyristors are discussed. The tradeoff of forward voltage drop with turn-off time and the effects of turn-off time vs. reapplied dV/dt are also discussed.

[54] M. F. Schlecht and B. A. Miwa, "Active power factor correction for switching power supplies," IEEE Transactions on Power Electronics, vol. PE-2, no. 4, pp. 273-281, 1987.

The harmonic-free utility/dc interface provides to the computer industry a means to extract more power from the wall outlet than the normal rectifier, with its heavily distorted input current, will allow. Due in part to the very high switch stresses in this interface, however, the cost appears to be too high to justify its use at this time. An alternate approach is proposed that focuses on power factor correction rather than harmonic reduction. Compared to the harmonic-free interface, the switch stress of this approach is approximately a factor of two smaller.

[55] L. E. LaWhite and M. F. Schlecht, "Active filters for 1-mhz power circuits with strict input/output ripple requirements," IEEE Transactions on Power Electronics, vol. PE-2, no. 4, pp. 282-290, 1987.

As the switching frequency of a dc converter is raised from 1000 kHz to 1 MHz, one would expect the energy storage elements of the circuit to be correspondingly reduced in size. If the circuit must meet input and output ripple requirements of the nature of MIL-STD-461B CEO3, however, the advantage of a higher switching frequency is significantly offset by the higher filter attenuation levels required. The use of active filters, in conjunction with minimal passive filters, to achieve the required ripple levels with a much smaller overall volume is discussed. Working active filters with gains in excess of 100 at 1 MHz are also presented.

[56] A. K. S. Bhat and S. B. Dewan, "Analysis and design of a high-frequency resonant converter using lcc-type commutation," IEEE Transactions on Power Electronics, vol. PE-2, no. 4, pp. 291-301, 1987.

The modeling, analysis, and design of a high-frequency resonant converter using an LCC-type commutation circuit is presented. Constant-current model and state-space approaches are used for the analysis. Closed-form solutions are derived for the inverter under steady-state conditions. Experimental results obtained from a prototype converter under different loading conditions are compared with the theory.

[57] T. Szepesi, "Stabilizing the frequency of hysteretic current-mode dc/dc converters," IEEE Transactions on Power Electronics, vol. PE-2, no. 4, pp. 302-312, 1987.

A systematic investigation of methods to stabilize the operating frequency of hysteretic current-mode dc/dc converters through control of the current hysteresis is presented. The control laws for every power stage are derived, and two open-loop and two closed-loop circuits are shown and analyzed in detail. The interaction of the major voltage control loop and the frequency-control circuitry is also investigated for buck converters. It is shown that, if the average inductor current is programmed, the two mechanisms are independent, while if the peak inductor current is programmed, they are not. In the latter case, the frequency-control circuitry decreases the phase margin of the voltage control loop, which can lead to instability. Simple circuits are developed to implement the superior average inductor-current programming.

[58] K.-S. Tam and R. H. Lasseter, "Hybrid converter for hvdc applications," IEEE Transactions on Power Electronics, vol. PE-2, no. 4, pp. 313-319, 1987.

In view of the growing use of high-voltage direct current (HVDC) the US as well as other countries, converter designs that can overcome the shortcomings of the conventional converter and support new applications of HVDC technology are being investigated. An HVDC converter is introduced that can operate without external reactive power compensation under any load conditions, control real and reactive power (or ac bus voltage) independently over a range of operation, and operate into weak ac systems without sophisticated converter control. The hybrid converter is found to be promising, and its full potential remains to be developed.

[59] E. Destobbeleer, G. Seguier, and A. Castelain, "Ac-dc converter minimizing induced harmonics in industrial power systems," IEEE Transactions on Power Electronics, vol. PE-2, no. 4, pp. 320-327, 1987.

Conventional ac-dc converters present two important disadvantages: they create harmonic currents and require reactive power. To reduce these drawbacks, a diode rectifier is directly connected in series with a chopper controlled by pulsewidth modulation. Both are preceded by a series inductance (added to the equivalent one of the power system) and a shunt capacitor. Results of a study on single-phase electric locomotives are given.

[60] J. McArdle, T. G. Wilson, Jr., and R. C. S. Wong, "Effects of power-train parasitic capacitance on the dynamic performance of dc-to-dc converters operating in the discontinuous mmf mode," IEEE Transactions on Power Electronics, vol. PE-2, no. 1, pp. 2-19, 1987.

A widely observed phenomenon is investigated in which a dc-to-dc converter operating in the discontinuous MMF (magnetomotive force) mode with a constant-frequency control law can exhibit wide variations in dynamic performance over a narrow range of input voltage or output load. This behavior is shown to be related to the sinusoidal energy exchange between the parasitic capacitances of the power stage and the energy-storage reactor during the discontinuous MMF mode of operation. The resulting ringing can cause dramatic variations in the apparent gain of the power train, thereby affecting the dynamic performance of the power supply. A new large-signal computer simulation technique is used to compare theoretical results with actual measurements.

[61] J. C. Bendien, H. Van der Broeck, and G. Fregien, "Recovery circuit for snubber energy in power electronic applications with high switching frequencies," IEEE Transactions on Power Electronics, vol. 3, no. 1, pp. 26-30, 1988.

A simple, reliable circuit is presented that allows snubber energy to be recovered by using a self-oscillating dc-to-dc converter. The applicability of the circuit is experimentally proved in three different types of power converters for electrical drives.

[62] P. K. Sood, T. A. Lipo, and I. G. Hansen, "Versatile power converter for high-frequency link systems," IEEE Transactions on Power Electronics, vol. 3, no. 4, pp. 383-390, 1988.

A single-phase high-frequency link appears to be an attractive alternative to the DC link commonly used in power conversion systems. The authors propose a power converter suitable for one-step conversion of the single-phase high-frequency link voltage to the three-phase low-frequency voltages typically required for interfacing with system sources and loads. The converter utilizes zero voltage switching principles to minimize switching losses and uses an easy-to-implement technique of pulse density modulation for the control of the amplitude, frequency, and waveshape of the synthesized low-frequency signals. Adaptation of the proposed topology for power conversion to single-phase AC and DC voltage or current outputs is shown to be straightforward. The feasibility of the proposed power circuit and the control technique have been experimentally verified.

[63] K. Thorborg and A. Nystrom, "Staircase pwm: An uncomplicated and efficient modulation technique for ac motor drives," IEEE Transactions on Power Electronics, vol. 3, no. 4, pp. 391-398, 1988.

An optimized staircase PWM (pulse-width modulation) is presented. The fundamental voltage component U₍₁₎ is proportional to the staircase amplitude M. Values of U₍₁₎ higher than 90% of the corresponding value for the nonmodulated waveform are attained for M = 1. The staircase is not a sampled representation of a sine wave and the number of steps and the frequency ratio are selected for a desired output voltage quality. A criterion for evaluating the quality of the output voltage, the weighted relative harmonic content, is presented. The control logic is uncomplicated and implemented by inexpensive complementary metal-oxide semiconductor logic with high noise immunity and reliability. The results have been verified by tests.

[64] A. I. Alolah, L. N. Hulley, and W. Shepherd, "Three-phase neutral point clamped inverter for motor control," IEEE Transactions on Power Electronics, vol. 3, no. 4, pp. 399-405, 1988.

A microprocessor-controlled PWM (pulse-width-modulated) inverter has been developed in which the neutral point at a star-connected load is clamped in potential. In addition to PWM waveforms, the inverter can generate six-step or eight-step waveforms in response to the appropriate software, using MC68000 microprocessor. Operation takes place in the PWM model for 1-40 Hz and in a step mode for 40-100 Hz. The inverter used 12 power switches compared with the customary six switches in a standard inverter. Darlington power transistors were used in a laboratory prototype rated at 6 kW. A design feature is that power to the drive circuits of the twelve switches comes directly from the DC supply, eliminating the need for individual power supplies. The root-mean-square value of the fundamental line voltage is 0.64 V DC compared to 0.5 V DC for conventional PWM operation with a six-switch inverter.

[65] K. Harada, H. Sakamoto, and M. Shoyama, "Phase-controlled dc-ac converter with high-frequency switching," IEEE Transactions on Power Electronics, vol. 3, no. 4, pp. 406-411, 1988.

An analysis of the phase-controlled DC-AC converter is presented. This converter has a pair of switches in each side of the primary and the secondary of the isolation transformer. The voltage conversion ratio is controlled by the phase difference between the two pairs of switches. The averaged equivalent circuit for low frequency is derived. The switching surge during commutation is much reduced by dividing the reactor into two parts. As a result, the transformer is miniaturized by increasing the switching frequency and the reactive energy can be easily recovered to the DC source. This DC-AC converter is especially suitable for small uninterruptible power supply systems.

[66] F. Kurokawa and H. Matsuo, "New multiple-output hybrid power supply," IEEE Transactions on Power Electronics, vol. 3, no. 4, pp. 412-419, 1988.

A novel hybrid power supply to perform the precise regulation of multiple-output voltages is presented. It is composed of the improved forward-type multiple-output converter as a preregulator and the continuous series regulators using MOSFETs as voltage droppers. The steady-state and the dynamic cross-regulation characteristics are analyzed and compared theoretically and experimentally for the conventional and improved forward-type multiple-output converters. As a result, it is clearly demonstrated that the improved forward-type multiple-output converter is superior to the conventional one in terms of steady-state and dynamic cross-regulation characteristics, and that the proposed multiple-output power supply has sufficiently precise regulation characteristics of the multiple-output voltages and a satisfactorily high power efficiency.

[67] M. Depenbrock, "Direct self-control (dsc) of inverter-fed induction machine," IEEE Transactions on Power Electronics, vol. 3, no. 4, pp. 420-429, 1988.

The new 'direct self-control' (DSC) is a simple method of signal processing that gives converter-fed three-phase machines an excellent dynamic performance. To control the torque of, e.g., an induction motor, it is sufficient to process the measured signals of the stator currents and the total flux linkages only. In the basic version of DSC the power semiconductors of a three-phase voltage source inverter are directly switched on and off via three Schmitt triggers, comparing the time integrals of line-to-line voltages to a reference value of desired flux, if the torque has not yet reached an upper-limit value of a two-limit torque control. Optimal performance of drive systems is accomplished in steady state as well as under transient conditions by combination of several two-limit controls. The expenses are less than in the case of proposed predictive control systems or the flux acceleration method, if the converter's switching frequency has to be kept minimal.

[68] W.-J. Gu and K. Harada, "New method to regulate resonant converters," IEEE Transactions on Power Electronics, vol. 3, no. 4, pp. 430-439, 1988.

A resonant frequency-modulation method is presented as an alternative to the switching frequency-modulation method to regulate resonant converters. A switch-controlled inductor and switch-controlled capacitor, in which switching losses are found to be very low due to zero-current or zero-voltage switching, are developed to do so. A new family of resonant converters that are regulated at a fixed switching frequency is proposed. A steady-state analysis of the Class E resonant converter regulated by a switch-controlled capacitor is presented. Theoretical and experimental results verify the validity of the proposed method. The efficiency measured from a breadboard of a 1-MHz, 5-V, 25-W Class E regulated resonant DC-DC converter is up to 83%.

[69] C. W. Lee and S. B. Park, "Design of a thyristor snubber circuit by considering the reverse recovery process," IEEE Transactions on Power Electronics, vol. 3, no. 4, pp. 440-446, 1988.

Design procedures are presented for the snubber circuit in power electronic circuits by considering the reverse recovery process of the thyristor. The thyristor turnoff model, whose parameters are determined for best fitting to the device characteristics given on the data sheets, is applied to analyze the behavior of the snubber circuit with and without a saturable reactor during reverse recovery time of the power device. Based on the turnoff model, exact expressions are derived for various quantities of interest including the maximum device stress, maximum reverse dv/dt, the reverse energy loss of a power device, and the total turnoff loss in the device plus the associated snubber circuit. Utilizing the analysis results, a systematic approach to the snubber-circuit design with the stray inductance taken into account is described. It is concluded that the proposed approach is very useful in the simulation of turnoff characteristics of the power device, snubber-circuit designs, and loss calculations in power circuits.

[70] T. M. Undeland and N. Mohan, "Overmodulation and loss considerations in high-frequency modulated transistorized induction motor drives," IEEE Transactions on Power Electronics, vol. 3, no. 4, pp. 447-452, 1988.

A model for calculating additional induction-motor losses due to harmonics associated with PWM (pulse-width-modulated) voltage-source inverters is presented. A simple and low-cost measurement using a small inverter to calculate the coefficients to be used in this loss model is presented for any size induction motor. Based on measurements of motor losses from 300 Hz to 10 kHz, the proposed model assumes much higher losses at higher voltage harmonics than the conventional models. It is shown that sine-wave modulation at ~ 3.6 kHz modulation frequency results in higher losses than the six-step operation, while there is a loss minimum at overmodulation. It is concluded that the proposed model will be useful for the evaluation of various modulation schemes for high-frequency transistor inverters.

[71] O. Stihi and B.-T. Ooi, "Single-phase controlled-current pwm rectifier," IEEE Transactions on Power Electronics, vol. 3, no. 4, pp. 453-459, 1988.

The analysis and test results are given of an experimental single-phase controlled-current PWM (pulse-width-modulated) rectifier that operates at unity power factor with near sinusoidal current waveform and that has power reversal capability. The twice-line-frequency AC power is identified as a source of voltage harmonics in the DC link. The harmonics enter into the voltage-regulation feedback loop to distort the AC current waveform. These undesirable harmonics can be removed by a low-pass filter. It is noted that the overall design must address the possibility of instability due to the low-pass filter in the feedback path.

[72] F.-S. Tsai, P. Materu, and F. C. Y. Lee, "Constant-frequency clamped-mode resonant converters," IEEE Transactions on Power Electronics, vol. 3, no. 4, pp. 460-473, 1988.

Two clamped-mode resonant converters are proposed which operate at a constant frequency while retaining desired features of conventional series- and parallel-resonant converters. State-plane analyses are performed which identify all possible circuit-operating modes of a clamped-mode series-resonant converter and define their mode boundaries. The control-to-output characteristics are derived to specify design regions for both natural and forced commutations. A breadboarded circuit was built to demonstrate the feasibility of the constant-frequency clamped-mode operation. All the predicted operating modes were verified experimentally.

[73] J. J. Cathey, S. F. Gorman, and J. A. Weimer, "Laboratory verification of modeling for a cycloconverter-fed microprocessor-controlled self-synchronous motor," IEEE Transactions on Power Electronics, vol. 3, no. 4, pp. 474-483, 1988.

The first known numerical simulation is presented of a cycloconverter-link self-synchronous motor drive operated by a discrete-time speed controller. Theoretically predicted and laboratory-measured transient and steady-state performances are compared to assess the accuracy of the model. The correlation between predictions made by the average value of motor phase current base simulation and the laboratory-measured performance shows that the model is quite adequate for steady-state analysis. Further, the model offers close prediction of speed during transient conditions, indicating that the associated half-cycle average values of current and the torque were reasonably accurate, although the capability of measuring the variables was not available. In addition, the general describing equations of motor phase currents during the commutation overlap interval are derived and numerically solved. Measured and predicted commutation overlap intervals for steady-state conditions are compared.

[74] R. D. Middlebrook, "Transformerless dc-to-dc converters with large conversion ratios," 1988, pp. 484.

A novel switching DC-to-DC converter is introduced in which large voltage step-down ratios can be achieved without a very small duty ratio and without a transformer. The circuit is an extension of the Cuk converter to incorporate a multistage capacitor divider. A particularly suitable application would be a 50-V to 5-V converter in which DC isolation is not required. The absence of a transformer and a larger duty ratio permits operation at a high switching frequency and makes the circuit amenable to partial integration and hybrid construction techniques. An experimental 50-W three-stage voltage divider Cuk converter converts 50 V to 5 V at 500 kHz, with efficiency higher than for a basic Cuk converter operated at the same conditions. A corresponding voltage-multiplier Cuk converter is described, as well as dual buck-boost-derived step-down and step-up converters.

[75] R. B. Ridley, B. H. Cho, and F. C. Y. Lee, "Analysis and interpretation of loop gains of multiloop-controlled switching regulators," IEEE Transactions on Power Electronics, vol. 3, no. 4, pp. 489-498, 1988.

Two different loop gains of power supplies with current-mode control are considered. Relationships between the different loop gains of the multiloop system and the closed-loop measures of output impedance and audio susceptibility are derived. It is shown that different loop gains can be used to obtain information about relative stability and to enhance a poor design. Different implementations of current-mode control are discussed, and the most common problem encountered in practical circuit applications is shown. This problem is connected with the fact that, for high-power applications, the dc portion of the waveform is much larger than the ramp.

[76] R. B. Ridley, "Secondary lc filter analysis and design techniques for current-mode-controlled converters," IEEE Transactions on Power Electronics, vol. 3, no. 4, pp. 499-507, 1988.

Small-signal characteristics of current-mode-controlled PWM converters with a second-stage LC filter are analyzed. It is shown that a secondary filter can be designed to provide good attenuation of the switching ripple while maintaining adequate stability margins with capacitive loading. The resonant frequencies and damping coefficients of the second filter are derived, and design guidelines are given. It is shown that the current-loop gain of the buck converter is not affected by the addition of the second-stage filters when a small filter inductance is used. Three design examples are presented to demonstrate the use of analysis results. Two filter examples are designed for a buck converter. One of the second filters shows the problems that arise with a poor design. A third example is the design of a second-stage filter for a buck-boost converter. In each of the design examples, the small-signal analysis was performed using EASY5 software, and the circuits were simulated using the state-space simulation program COSMIR.

[77] T. A. Lipo, "Recent progress in the development of solid-state ac motor drives," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 105-117, 1988.

The author summarizes important developments in AC drive design that have occurred in the past several years. He discusses: (1) converter technology, covering the matrix converter, PWM voltage and current link converters, and resonant link converters; (2) AC motor technology, covering stepping motor drives, DC brushless motor drives, and synchronous reluctance motors; and (3) control technology for AC drives, covering online and offline parameter identification and efficiency-maximizing control.

[78] A. Kawamura, T. Haneyoshi, and R. G. Hoft, "Deadbeat controlled pwm inverter with parameter estimation using only voltage sensor," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 118-125, 1988.

A technique based on deadbeat control theory is proposed to obtain a nearly sinusoidal PWM (pulsewidth-modulated) inverter output voltage using only a voltage sensor. The closed-loop sampled-data feedback scheme inherently results in very fast response to load disturbance and nonlinear load, producing low total harmonic distortion. Parameter estimation of the plant provides a type of self-tuning of the proposed controller. A theoretical analysis and simulation and experimental results are presented for a single-phase PWM inverter controlled by an Intel 8086 microprocessor.

[79] M. K. Kazimierczuk, "Design-oriented analysis of boost zero-voltage-switching resonant dc/dc converter," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 126-136, 1988.

Analysis and design procedures are presented for a high-efficiency, high-frequency, boost zero-voltage-switching resonant DC/DC power converter. Equations describing converter operation are derived. The basic performance parameters of the circuit are analyzed as functions of the normalized load resistance and switching frequency. Those equations are then used to determine conditions for lossless converter operation and design equations that yield the required component values.

[80] R. B. Prest and J. D. Van Wyk, "Pulsed transformer base drives for high-efficiency high-current low-voltage switches," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 137-146, 1988.

An overview of the literature on base drives is followed by a description of a novel transformer-coupled base drive circuit that is particularly suitable for high-current transistor switches. It has the advantages of very low component count and cost, small size, and high efficiency with no driver transistors being rated at full base current. The operation of the main transistor in deep saturation results in low conduction losses, and the dynamic characteristics of the switch are shown to be suitable for inverter applications. A simple mathematical model is proposed and experimental results on a drive for a 350-A 100-V switch are given.

[81] R. L. Maresca, "400-w tri-state switching controller for reciprocating linear motors," IEEE Transactions on Power Electronics, vol. 3, no. 1, pp. 3-9, 1988.

A switching controller is described that uses stable limit-cycle theory and phase-locked-loop control for high-power reciprocating linear motor systems. The control system comprises a low-frequency tristate switching circuit, a linear motor, and an axial position sensor along with three distinct feedback loops (peak-amplitude feedback, average-position feedback, and phase feedback). The system was tested on a 400-W reciprocating compressor and achieved efficiencies of greater than 90% with excellent control of the critical operating parameters: speed, stroke, phase, and center position of the linear motor. The system replaces a 70%-efficient high-frequency switching amplifier and classical servo-control system previously used in long-life Stirling-cycle refrigerators for space applications. 5 refs.

[82] B. Wu, S. B. Dewan, and P. C. Sen, "Modified current source inverter (mcsi) for a multiple induction motor drive system," IEEE Transactions on Power Electronics, vol. 3, no. 1, pp. 10-16, 1988.

A modified current-source inverter (MCSI) that can drive multiple motors is presented. The MCSI combines the features of the current-source inverter and the voltage-source inverter. It also overcomes major shortcomings of the current-source inverter. The commutation process of the inverter is described. Design considerations are briefly introduced. Some experimental results are given for five 1-hp induction motors running in parallel from a single MCSI.

[83] A. L. Melse and S. W. H. de Haan, "Reactive power handling with series-resonant converters," IEEE Transactions on Power Electronics, vol. 3, no. 1, pp. 17-25, 1988.

A description is given of a series-resonant reactive power compensator based on a series-resonant converter topology. The compensator delivers high-quality sinusoidal waveforms, while it preserves the advantages of resonant converters, such as low switching losses and low component stress, improved reliability, low electromagnetic interference (EMI), and low size and weight of components. The topology and associated switching schemes are derived. Simulation results are presented and measured waveforms are shown for a 1-kVa compensator.

[84] G. K. Schoneman and D. M. Mitchell, "Closed-loop performance comparisons of switching regulators with current-injected control," IEEE Transactions on Power Electronics, vol. 3, no. 1, pp. 31-43, 1988.

The authors verify the validity of applying state-space averaging and linearization to the control law of current-injected switching regulators for designs with wideband first-order open-loop responses without right-hand plane (RHP) zeros. Quantitative closed-loop performance comparisons are made of current-injected versus voltage control for the boost and buck switching regulator topologies. In buck-topology regulators, current-injected control implemented using pole cancellation, does not yield categorically better closed-loop performance than what is obtained by using lead compensated voltage control. For the boost regulator, the advantages of current-injected control are greater since lead-compensation cannot usually be used due to the duty-factor-dependent complex pole and RHP zero.

[85] B. H. Cho and F. C. Y. Lee, "Modeling and analysis of spacecraft power systems," IEEE Transactions on Power Electronics, vol. 3, no. 1, pp. 44-54, 1988.

A comprehensive large-scale power system modeling technique using the multiport coupling method is developed to facilitate design and analysis of present and future spacecraft power systems. The Boeing Computer Service's EASY5 program was used as the host software to meet various modeling and analysis needs for dc, small-signal, and large-signal analyses. Power subsystem or component model development from empirical data and reduced-order model generation using the complex curve-fitting technique are also introduced. A sample spacecraft power system, the simplified Direct Energy Transfer system, is modeled and its performance demonstrated.

[86] K. D. T. Ngo, "Analysis of a series resonant converter pulsewidth-modulated or current-controlled for low switching loss," IEEE Transactions on Power Electronics, vol. 3, no. 1, pp. 55-63, 1988.

Pulsewidth modulation (PWM) and current-controlled switching are applied to a full-bridge series resonant converter to regulate the output from no load to full load with low switching loss and with a narrow range of frequency variation. Drive strategies, control law, component stress, and other steady-state functions are analyzed for both switching modes. The range of frequency variation of the resulting switching scheme is narrower than that of a normal square-wave drive. It is noted that the advantages of low switching stress and narrow band frequency variation can be extended over the entire range of voltage gain or load by combining PWM with current-controlled switching.

[87] M. F. Schlecht and L. F. Casey, "Comparison of the square-wave and quasi-resonant topologies," IEEE Transactions on Power Electronics, vol. 3, no. 1, pp. 83-92, 1988.

The waveforms of a square-wave dc-dc converter and a quasiresonant dc-dc converter are examined in detail and a comparison is made between the switching losses and conduction losses for each topology. Using data from commercially available semiconductor devices, conservative estimates are then given for the switching frequency at which the resonant approach becomes advantageous. The effect of an isolation transformer on this comparison is also addressed.

[88] T. Ninomiya, T. Tanaka, and K. Harada, "Analysis and optimization of a nondissipative lc turn-off snubber," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 147-156, 1988.

A nondissipative LC turn-off snubber is used to reduce the voltage stress on a switching transistor, which is caused by the energy stored in the transformer leakage inductance. A detailed analysis of the fundamental characteristics of a buck-boost converter with an LC snubber is given, clarifying the effect of the snubber capacitance. In particular, it is found that the transformer current increases with the snubber capacitance. The transistor surge voltage and power loss are evaluated, and the optimum value of the snubber capacitance is derived. The most effective value of the snubber inductance is also discussed.

[89] A. Caruso, P. Spirito, G. Vitale, G. Busatto, G. Ferla, and S. Musumeci, "Performance analysis of a bipolar mode fet (bmfet) with normally off characteristics," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 157-163, 1988.

The fabrication and characterization of a family of power bipolar-mode junction FETs (BMFETs) are reported. Blocking voltages up to 1000 V or currents up to 18 A (corresponding to 800 A/cm**2) have been obtained. The experimental results are used to get an insight into the physics of BMFET operation and to extract the basic design criteria for these structures. The performance of the BMFET is compared with that of the bipolar transistor, showing it to be superior.

[90] R. L. Steigerwald, "Comparison of half-bridge resonant converter topologies," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 174-182, 1988.

The half-bridge series-resonant, parallel-resonant, and combination series-parallel resonant converters are compared for use in low-output-voltage power supply applications. It is shown that the combination series-parallel converter, which takes on the desirable characteristics of the pure series and the pure parallel converter, avoids the main disadvantages of each of them. Analyses and breadboard results show that the combination converter can run over a large input voltage range and a large load range (no load to full load) while maintaining excellent efficiency. A useful analysis technique based on classical AC complex analysis is introduced.

[91] H. W. van der Broeck and H.-C. Skudelny, "Analytical analysis of the harmonic effects of a pwm ac drive," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 216-223, 1988.

A novel analysis is presented of the harmonic content of current, torque pulsations, and harmonic copper losses of a three-phase induction machine fed by a two-phase pulsewidth modulation (PWM) inverter. The purely analytical results are based on the assumption that the switching frequency is high compared with the fundamental frequency. It is shown that the results hold accurately for frequency ratios f//s/f//1 greater than 9.

[92] J. B. Klaassens, W. L. F. H. A. Moize de Chateleux, and M. P. N. van Wesenbeeck, "Phase-staggering control of a series-resonant dc-dc converter with paralleled power modules," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 164-173, 1988.

A method of decreasing the ripple on the output voltage of high-power AC-DC or DC-DC series-resonant converters without increasing the internal converter frequency or the capacity of the energy storage elements is discussed. This improvement is accomplished by subdividing the converter into two or more series-resonant power modules operated with a constant relative phase shift (phase-staggering control). The method of eliminating the harmonic components in the input and output currents of the conversion system, without increasing the internal pulse frequency, is justified by Fourier analysis of the current waveforms. The frequency spectra of the source and output waveforms for the continuous and discontinuous resonant current mode are shifted to higher frequency ranges. Inadequacies in the phase-staggering control method applied to series-resonant converters are indicated in relation to the dominant harmonic component. High-frequency current components to the source and to the load are reduced, resulting in smaller input and output filters. This improves the resolution of the control of the flow of energy from the source to the load, resulting in a faster system response.

[93] V. Vorperian, "Quasi-square-wave converters: Topologies and analysis," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 183-192, 1988.

A class of converters with zero-voltage or zero-current switching characteristics is analyzed using a method originally developed for quasiresonant and PWM (pulsewidth-modulated) converters. The method relies on identifying simple three-terminal structures, called converter sections, that contain the switches and the resonant tank elements. The various zero-voltage-switched and zero-current-switched converters are obtained by permutation of these converter sections between source and sink. The method unifies the analysis of this class of converters in a single equivalent circuit model. The voltage and current waveforms in these converters are essentially squarelike except during the turn-on and turn-off switching intervals.

[94] B. T. Ooi, J. W. Dixon, A. B. Kulkarni, and M. Nishimoto, "Integrated ac drive system using a controlled-current pwm rectifier/inverter link," IEEE Transactions on Power Electronics, vol. 3, no. 1, pp. 64-71, 1988.

Two identical three-phase, bipolar transistor, controlled-current, pulsewidth modulation (PWM) power modulators are integrated so that one functions as a rectifier and the other as an inverter in an ac drive system. The rectifier input currents maintain near-60-Hz sinusoidal waveforms with unity power factor. A leading power factor is also possible. The modulators do not depend on the availability of bidirectional switch elements. Performance as a polyphase induction motor drive under motoring and regenerative braking is reported. The study includes digital simulation of operation as a synchronous motor drive.

[95] L. F. Casey and M. F. Schlecht, "High-frequency, low volume, point-of-load power supply for distributed power systems," IEEE Transactions on Power Electronics, vol. 3, no. 1, pp. 72-82, 1988.

A resonant version of the dc-dc forward converter is presented in which both the primary-side switch and the secondary-side diode are either on or off at the same time. Such a topology is capable of operation in the 10-MHz range, and can be used for very-low-volume point-of-load conversion in distributed power systems. This type of converter takes advantage of a very low transformer leakage inductance to achieve zero-voltage switching of all its power semiconductor devices. Its resonant ring is also independent of load current. A 50-W prototype operating at 3. 6 MHz is presented along with a discussion of the changes necessary to achieve 10 MHz.

[96] S. D. Johnson and R. W. Erickson, "Steady-state analysis and design of the parallel resonant converter," IEEE Transactions on Power Electronics, vol. 3, no. 1, pp. 93-104, 1988.

Five basic operating modes of the parallel resonant converter are analyzed. Three of the modes occur when the output filter inductor is removed and the remaining two occur when the filter inductor is large. Closed-form solutions are found for the two most important modes. Analysis results are given graphically so that the designer can use them without length calculation or computer iteration. Switching frequency, peak tank capacitor voltage, and peak tank inductor current are plotted in the output plane. These plots, with a load line superimposed, show how operating point, frequency, and peak stress vary as load conditions change. Use of the output plane plots to minimize component costs is explained. Comparison of the best designs found for the large and zero filter inductance cases shows that removing the filter inductor can reduce both parts count and tank circuit size while peak transistor current remains unchanged.

[97] S. K. Sul and M. H. Park, "Novel technique for optimal efficiency control of a current-source inverter-fed induction motor," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 192-199, 1988.

A technique that optimizes flux level to improve the efficiency of an induction motor is discussed. When harmonics and saturation effects are considered, the slip of minimum loss, or optimal slip, depends on both the speed and the load torque. The measurements of speed and torque are achieved without conventional torque and speed sensors, using motor terminal quantities. The control strategy is divided into two stages. First, the optimal slip is searched by trial and error, and the results are tabulated in microprocessor memory. Then the motor is operated at optimal efficiency by simply tracking the optimal slip given in the table. Experimental results show good performance in energy saving and dynamic responses.

[98] S. R. Doradla, S. Chakravorty, and K. E. Hole, "New slip power recovery scheme with improved supply power factor," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 200-207, 1988.

A slip power recovery scheme with a PWM (pulsewidth-modulation) converter in the rotor circuit is investigated. The steady-state performance characteristics, such as speed-torque characteristics and the overall power factor of the drive system, are determined using simple DC and AC equivalent circuits. The performance characteristics are verified experimentally, showing good agreement with theoretical results. The power factor of the drive system is improved significantly over the entire range of speed control. The drive provides speed-torque characteristics similar to those of a separately excited DC motor. Oscillograms of typical waveforms from the experimental setup are illustrated to demonstrate the satisfactory performance of the scheme.

[99] S. Deb, A. Joshi, and S. R. Doradla, "Novel frequency-domain model for a parallel-resonant converter," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 208, 1988.

A steady-state analysis of the parallel-resonant converter is presented using a novel frequency-domain model. Various circuit variables are determined by simple expressions for both the frequency and the phase control techniques, simplifying the steady-state analysis. The existence of a multiple conduction mode is pointed out. The variations of output voltage, turn-off time, output power, and converter efficiency are studied.

[100] Y. Kim, S. Okuma, and K. Iwata, "Characteristics and starting method of a cycloconverter with a tank circuit for induction heating," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 236-244, 1988.

A cycloconverter with a tank circuit for induction heating is presented that can deliver power to load while keeping the input displacement factor at 1. 0 is proposed. Static characteristics are analyzed using the switching functions and mode functions, and operating regions in which the input displacement factor is kept at 1. 0 are found. A starting method that uses only a gate pulse sequence for thyristors to establish the tank voltage is proposed. The starting method is simulated to determine feasibility. Experimental results are presented that are in good agreement with theory.

[101] R. B. Prest and J. D. Van Wyk, "Reverse bipolar transistor conduction in high-current pwm inverters," IEEE Transactions on Power Electronics, vol. 3, no. 3, pp. 246-253, 1988.

Most PWM (pulse width-modulated) converters using bipolar transistors experience the problem of reverse transistor conduction. This effect is analyzed for various types of base drives. It is shown to be the most serious for low-impedance direct drives. A model is developed for this case and verified experimentally. Problems associated with turn-on and turn-off in the reverse conduction mode are investigated. Various base drives, including both direct drives and Darlington configurations, are analyzed. Reverse transistor conduction is found to have the most serious implications for transistors driven directly by a low impedance source. Although discrete devices are discussed, the results apply to integrated Darlington modules as well.

[102] K. N. Pavithran, R. Parimelalagan, and M. R. Krishnamurthy, "Studies on inverter-fed five-phase induction motor drive," IEEE Transactions on Power Electronics, vol. 3, no. 2, pp. 224-235, 1988.

The advantages of higher-phase-order drives are reviewed, and results of investigations of a five-pulse inverter-fed induction motor are presented. Methods of improving the waveform of the motor phase current in the five-phase drive are examined theoretically as well as experimentally. A mathematical model based on complex symmetrical components is developed for theoretical investigations, and a prototype five-phase inverter-fed induction motor drive is fabricated to conduct experimental studies. Theoretical and experimental results under various operating modes are presented. The studies establish that the five-phase drive operates satisfactorily when it is fed from a pulsewidth-modulated inverter.

[103] M. K. Kazimierczuk, "Steady-state analysis and design of a buck zero-current-switching resonant dc/dc converter," IEEE Transactions on Power Electronics, vol. 3, no. 3, pp. 286-296, 1988.

An analytic basis is provided for a buck high-efficiency high-frequency zero-current-switching resonant DC/DC power converter. The current and voltage waveforms are derived for the steady-state operation. Design equations are then introduced for the switch duty cycle, maximum switching frequency, DC transfer function, peak currents and voltages, output power, and power conversion capability. Finally, the design procedure is presented along with the advantages and disadvantages of the converter, which are discussed in detail.

[104] J. Hamman and F. S. van der Merwe, "Voltage harmonics generated by voltage-fed inverters using pwm natural sampling," IEEE Transactions on Power Electronics, vol. 3, no. 3, pp. 297-302, 1988.

The harmonics generated by natural sampled pulsewidth modulation are investigated experimentally and by theoretical models for the outputs obtained with triangular and sawtooth carrier signals. These equation are valid for synchronous and asynchronous operation. It is shown that triangular carriers generate less harmonics than sawtooth carriers, and that in synchronous operation with single-phase modulation, the carrier-to-output frequency ratio may be any integer value.

[105] H. Akagi, T. Sawae, and A. Nabae, "130 khz 7.5 kw current source inverters using static induction transistors for induction heating applications," IEEE Transactions on Power Electronics, vol. 3, no. 3, pp. 303-309, 1988.

A control scheme of a high-frequency high-power current source inverters using static induction transistors is described which aims at the suppression of the surge voltage and reduction of the switching loss during the commutation of current. The inverter is operated at a leading power factor, which requires the phase angle of the output current to be adjusted to each specific load point by the controller. The stable operation is verified by the experiments under the commutation inductance 1.8 μH, i.e., 18% reactance (130 kHz, 250 V, 30 A, base). As a result, the inverter efficiency is estimated to be 97%, excluding the loss of the drive circuit and the control circuit.

[106] L. LaWhite and M. F. Schlecht, "Design of active ripple filters for power circuits operating in the 1-10 mhz range," IEEE Transactions on Power Electronics, vol. 3, no. 3, pp. 310-317, 1988.

A fundamental analysis of active ripple filters for power circuits operating in the 1-10 MHz range is presented. The improved understanding derived from this analysis allows filter circuits with gains five to ten times higher than previously reported to be built. Besides providing further reduction in the size of 1 MHz ripple filters, these higher gains make the active filters valuable for power circuit switching near 10 MHz.

[107] Y.-G. Kang and A. K. Upadhyay, "Analysis and design of a half-bridge parallel resonant converter," IEEE Transactions on Power Electronics, vol. 3, no. 3, pp. 254-265, 1988.

A half-bridge parallel resonant converter (PRC) is analyzed in detail for both continuous-conduction-mode and discontinuous-conduction-mode operations to provide more straightforward and easy-to-use design tools. Closed-form solutions are derived for the PRC operating under steady-state conditions. Theoretical results obtained are presented in the form of normalized design graphs. They could be directly utilized in designing a half-bridge PRC, having up to 2:1 input voltage variation. They do not necessitate converting the obtained ratings, depending on the input voltage and load variations, to check the worst case values. A design example of a 500-KHz 150-W offline switching power supply is given for both modes of operation, and it is implemented for experimental verification.

[108] J.-P. Vandelac and P. D. Ziogas, "Novel approach for minimizing high-frequency transformer copper losses," IEEE Transactions on Power Electronics, vol. 3, no. 3, pp. 266-277, 1988.

A graphical and numerical method of calculating and minimizing losses in windings, that generalizes previous findings, has been introduced. Using electromagnetic theory and MMF diagrams in both space and time, a method is proposed that provides insight into the mechanism of skin and proximity effect losses and that also yields quantitative results. Using this method, several winding geometries for various topologies are covered. The analysis and optimization process is experimentally verified using an interleaved flyback transformer. The mathematical treatment justifying the use of the field method and which is essential in arriving at any numerical result is presented and more general equations for the calculation of copper losses are derived. The relation between the fields in the transformer and copper losses is emphasized. Also, the tools necessary to derive optimization diagrams are provided.

[109] J. Holtz, W. Lotzkat, and K.-H. Werner, "High-power multitransistor-inverter uninterruptible power supply system," IEEE Transactions on Power Electronics, vol. 3, no. 3, pp. 278-285, 1988.

The active and reactive load distribution between n paralleled single-phase uninterruptible power supply (UPS) inverters is equalized by virtue of n-1 load-sharing control loops. The approach permits the construction of UPS systems of any desired power rating at maximum utilization of the power components. The method of harmonic cancellation decreases the switching frequency of the power devices while maintaining good dynamic performance. The design details of a 45-kVa UPS inverter system with 150% steady-state overload capability are presented. The performance under various operating conditions is illustrated by oscillograms.

[110] R. Oruganti, J. J. Yang, and F. C. Lee, "Implementation of optimal trajectory control of series resonant converter," IEEE Transactions on Power Electronics, vol. 3, no. 3, pp. 318-327, 1988.

Optimal trajectory control was proposed based on the insight gained from a state-plane analysis, which is summarized. By utilizing the required transistor trajectory as the control law, this control method attempts to reach its steady-state operation in a time-optimal manner. The control automatically selects the optimum sequence of device conduction under all dynamic conditions. An implementation scheme for this control method was presented. The scheme reduces the complexity of the control method by making efficient use of the control circuit elements. The scaling procedure used to determine and set the scaling factors in the control scheme was also described. The transient response of the converter with optimal trajectory control was excellent as predicted. Comparison with the frequency-control method confirms the superior dynamic performance of the optimal trajectory control.

[111] K. Taniguchi, Y. Ogino, and H. Irie, "Pwm technique for power mosfet inverter," IEEE Transactions on Power Electronics, vol. 3, no. 3, pp. 328-334, 1988.

A sinusoidal PWM (pulsewidth-modulated) inverter suitable for use with power MOSFETs is described. The output waveforms in the proposed PWM inverter are investigated both theoretically and experimentally. A modulating signal for the three-phase PWM inverter is obtained by adding the harmonic components of integer multiples of three to the three-phase sine waves. By using the proposed modulating signal, the amplitude of the fundamental component is increased about 15% more than that of a conventional sine-wave inverter and the commutation number of the inverter is decreased to two-thirds of a conventional one.

[112] J. B. Klaassens and E. J. F. M. Smits, "Series resonant ac-power interface with an optimal power factor and enhanced conversion ratio," IEEE Transactions on Power Electronics, vol. 3, no. 3, pp. 335-343, 1988.

A method of power pulse modulation with internal frequencies of tens of kHz which is also suitable for multikilowatt power levels is applied to a series-resonant converter system for generating synthesized multiphase bipolar waveforms with reversible power flow. The power circuitry of the converter is provided with one single high-frequency resonant link in the direct energy path. Natural current commutation of the thyristors is obtained by the use of a series-resonant circuit for power transfer and control. Consequently, switching losses can be reduced to a minimum without compromising the reliability of the solid-state components. Test results of a converter system generating three-phase sinusoidal waveforms demonstrate the significant aspects of this improved series-resonant power processor and indicate the possibilities of fast-acting DC and AC converter systems with reversible power flow.

[113] M. E. Elbuluk, G. C. Verghese, and J. G. Kassakian, "Sampled-data modeling and digital control of resonant converters," IEEE Transactions on Power Electronics, vol. 3, no. 3, pp. 344-354, 1988.

A sampled-data model to describe the dynamics of large signals and of small perturbations away from a cyclic steady state is developed. Associated transfer functions are obtained. The application of the model is illustrated by correlating the analysis with simulation results obtained for a series-resonant DC-DC converter. A discrete-time microprocessor-based controller, designed using the aforementioned dynamic model, has been built and tested on a simulation for a series-resonant DC--DC converter set up on the Massachusetts Institute of Technology Parity Simulator. The control methods implemented are state feedback and periodic output feedback, each designed to achieve state feedback and periodic output feedback, each designed to achieve a specified set of closed-loop poles. The controller has been implemented using the Parity Simulator generalized controller. Results of the closed-loop response showed an improvement over the open-loop response. In addition, the effect of the microprocessor computation delay on the closed-loop dynamics of the converter is investigated. Results have been shown that this delay can be important and should be modeled in the dynamics when designing the controller.

[114] A. K. S. Bhat and S. B. Dewan, "Analysis and design of a high-frequency link dc to utility interface using square-wave output resonant inverter," IEEE Transactions on Power Electronics, vol. 3, no. 3, pp. 355-363, 1988.

A line-current-modulated high-frequency (HF) link DC to utility interface power conditioning system using a square-wave output resonant inverter is proposed. The proposed system consists of a square-wave output HF resonant inverter, a rectifier, and a line-connected inverter. The system is modeled using the constant current model for the HF inverter and the step model for the DC link current. The operating modes, analysis, design, and experiment results are presented. It has been shown that systems operating with less than 5% line current harmonic distortion are realizable when the type II commutation scheme is used for the LCI. A typical application of the system presented is in interfacing photovoltaic arrays to utility lines.

[115] F.-S. Tsai, Y. Chin, and F. C. Y. Lee, "State-plane analysis of a constant-frequency clamped-mode parallel-resonant converter," IEEE Transactions on Power Electronics, vol. 3, no. 3, pp. 364-378, 1988.

A novel clamped-mode parallel-resonant converter which operates at a constant frequency and provides a wide output regulation range is proposed and analyzed. Employing graphical state-plane techniques, five circuit operating modes are identified and their mode boundaries defined. Regions for natural and forced commutation of power devices are specified. The DC control-to-output characteristics are derived to facilitate converter design. The predicted operating modes are experimentally verified using a 105-kHz prototype circuit.

[116] R. W. Erickson, A. F. Hernandez, A. F. Witulski, and R. Xu, "Nonlinear resonant switch," IEEE Transactions on Power Electronics, no. 242-252, 1989.

A resonant switch is introduced that uses linear tank elements. Zero-current switching is obtained even though the peak transistor voltage and current stresses can approach those of an equivalent ideal pulsewidth-modulated converter. Reduced switching loss without a substantial increase in conduction loss is therefore possible. An approximate analysis is outlined, and transistor peak-voltage and current stresses are shown to be much lower than those of linear resonant switch technologies. Single-transistor implementations of the buck, boost, and buck-boost nonlinear resonant switch converters are given. Results are presented which experimentally prove the validity of the nonlinear resonant switch concept, as well as that of the approximate analysis.

[117] A. K. S. Bhat and S. B. Dewan, "Input-output harmonics of line-current-modulated high-frequency link dc to utility interface power converters," IEEE Transactions on Power Electronics, no. 253-264, 1989.

Two types of commutation schemes (called Type I and Type II) are proposed and analyzed for the line-connected inverter used in line-current-modulated high-frequency link DC to utility interface power conditioning systems. In the Type I scheme the high-frequency inverter is switched off well in advance of the zero crossings of line voltage, allowing the line current to go to zero and enabling the line-connected inverter to turn off. A simple lossless forced commutation circuit is used in the Type II scheme. The effects of these schemes on line-side and input DC-side current harmonics are studied in the case of single-phase systems, neglecting the effect of controller action. The performance indices are evaluated. The results obtained from prototype experimental systems are used to verify the theory presented. The analysis presented for single-phase systems is extended to three-phase systems.

[118] M. K. Kazimierczuk and W. D. Morse, "State-plane analysis of zero-current-switching resonant dc/dc power converters," IEEE Transactions on Power Electronics, no. 265-271, 1989.

The state-plane analysis for the buck, boost, buck/boost, and Cuk zero-current-switching resonant DC/DC power converters is presented. Simple visual criteria are introduced to determine whether the converter is operating in a mode producing voltage conversion. It is shown that the voltage conversion takes place within the converters if and only if both horizontal and vertical straight-line segments are present in the state-plane graph. The boundary of energy conversion is identified from the state plane by the evaporation of one or both straight-line segments. Formulas are found for the normalized switching frequency at this boundary that depend on the value of normalized switching voltage.

[119] A. K. Chattopadhyay and N. Meher, "Microprocessor implementation of a state feedback control strategy for a current source inverter-fed induction motor drive," IEEE Transactions on Power Electronics, no. 279-288, 1989.

The realization of a microprocessor-based controller which implements a complete state-feedback control strategy for a current source inverter-fed induction motor drive is reported. The controller design is based on the application of the pole assignment technique of multivariable system regulation theory to a d,q-axis state-space linearized model of the drive and includes a reduced-order observer to achieve fast regulation and stability. The observer is designed to reconstruct the inaccessible states such as d,q-axis rotor currents from a knowledge of the system inputs and outputs. The hardware and software implementation of the controller around an 8085-based microprocessor kit is discussed, and typical test results are presented, along with digital simulation results, to show its performance.

[120] R. J. Hill and F. L. Luo, "Microprocessor-based control of steel rolling mill digital dc drives," IEEE Transactions on Power Electronics, no. 289-297, 1989.

Algorithms are presented for the digital control of double-loop DC machine drives used for applications where severe constraints on motor speed and position render conventional constant-torque or power control inadequate, such as in steel rolling mill drives. It is shown that the heavy current demand associated with maximal acceleration control can be reduced by using a form of proportional control where, in addition to the conventional inner-loop current feedback, a distance feedback term sets the high limiting value of the speed feedback signal, thus reducing the motor armature current.

[121] G. Andria, L. Salvatore, and A. Dell'Aquila, "Analysis of distorted unbalanced waveforms in inverter drives," IEEE Transactions on Power Electronics, no. 298-310, 1989.

A method is proposed for the analysis of waveforms in a three-phase system when both distortion and unbalance are present. The analysis is carried out in the frequency domain and is based on the application of the fast Fourier transform (FFT) algorithm to a comple sequence representing the instantenous symmetrical components of the distorted and unbalanced three-phase waveforms. By theoretical analysis it is shown that the first half of the spectrum returned by the FET algorithm represents the area of the harmonic components that rotate counter-clockwise, whereas the last half of the spectrum represents the area of harmonics that rotate clockwise. The method makes it possible to obtain the positive- and negative-sequence components of each harmonic system present in the three phases. This method also provides a way to get information both on the degree of unbalance and on the distortion factors of the waveforms generated by pulsewidth-modulated inverters supplying induction motors. A digital measurement system based on a personal computer was set up and the proposed analysis procedure was implemented. The experimental analysis of a commercially available pulse-width modulation inverter was also carried out. The results prove the validity and power of the analysis procedure.

[122] R. Tymerski, V. Vorperian, and F. C. Y. Lee, "Dc-to-ac inversion using quasi-resonant techniques," IEEE Transactions on Power Electronics, vol. 4, no. 4, pp. 381-390, 1989.

It is demonstrated that two basic approaches can be taken to achieve DC-to-AC inversion. The first, the differential load excitation (DLE) scheme, uses two converters, driven out of phase, to drive a load differentially. Unfortunately, this scheme requires a large number of components when it is implemented using quasi-resonant techniques. A more component-effective approach uses switched source excitation (SSE) schemes. One SSE approach uses two converters, each handling one polarity of the signal. By appropriate switching, an amplified signal is reconstructed at the output. The second SSE approach entails only one converter but with a slightly more involved switching requirement. It allows a significant overall reduction in the number of components needed and reduced performance requirements on most of the switches, since most switch at the lower inversion-frequency rate. A number of quasi-resonant inverter topologies from two broad categories are presented. For applications that require inverters to supply reactive power, three schemes which can be applied to various inverters, thus affording them reactive load handling capability, are discussed.

[123] A. K. S. Bhat and M. M. Swamy, "Loss calculations in transistorized parallel resonant converters operating above resonance," IEEE Transactions on Power Electronics, vol. 4, no. 4, pp. 391-401, 1989.

The optimum operating point under certain constraints for a parallel resonant converter (PRC) operating above resonance is obtained. A systematic way to calculate losses in a PRC operating above resonance is presented and illustrated for bipolar and MOS power transistor switches. Experimental results obtained with prototype converters employing the above devices are given to support the theory. Both theory and experiments show that MOSFETs are better switching devices at a power level of about 1 kW.

[124] V. A. Sankaran, J. L. Hudgins, and W. M. Portnoy, "Role of the amplifying gate in the turn-on process of involute structure thyristors," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 125-132, 1989.

The switching characteristics of involute thyristors with and without the amplifying gate structure are discussed. The effects of peak gate currents (10-100 A) on the anode current di/dt, switching delay, and energy loss in both types of devices are presented. The performance of the devices without the amplifying gate was far superior than that of the devices with the amplifying gate. A model is presented to explain this difference. Thyristors without the amplifying gate successfully switched anode currents on the order of 12.6 kA, at a di/dt of 100,000 A/μs, from an anode voltage of 2 kV on a single-shot basis.

[125] S. Morimoto, Y. Takeda, and T. Hirasa, "Current phase control methods for permanent magnet synchronous motors," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 133-139, 1989.

Three types of current phase control methods are examined for the interior magnet motor and the surface magnet motor: (1) the i_d = 0 control method, (2) the cos φ = 1 control method, and (3) the constant-flux-linkage control method. The control circuits for realizing these control methods were investigated and a drive test carried out. The most suitable current phase control method for the rotor geometry was examined by computer simulation and experimentation. It was found that in the i_d = 0 control method, high-performance torque control can be obtained as the torque is proportional to the armature current. In the cos φ = 1 control method, the torque per armature current is small and the torque characteristic is nonlinear. Therefore, high-performance torque control cannot be expected. The constant-flux-linkage control method is desirable for interior magnet motors as the torque characteristic is almost linear and the required inverter capacity is comparatively small.

[126] I. Batarseh, R. Liu, C. Q. Lee, and A. K. Upadhyay, "Theoretical and experimental studies of the lcc-type parallel resonant converter," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 140-150, 1989.

Using the state-plane approach, the steady-state analysis and design of a high-frequency LCC-type parallel resonant converter (LCC PRC) operating in the continuous conduction mode are carried out. On the basis of this analysis, a set of steady-state characteristic curves for the LCC PRC is plotted. Various design curves for component value selection and device ratings are also presented. A simple design procedure is given, and a design example for a 150-W, 140-kHz multioutput LCC PRC power supply is presented for illustrative purposes. A prototype unit has been built and verifies the theoretical results.

[127] D. Y. Chen, J. Lee, and C. Jamerson, "Simple model predicts small-signal control loop behavior of magamp post-regulator," IEEE Transactions on Power Electronics, vol. 4, no. 4, pp. 402-408, 1989.

A block diagram approach is used to provide insight into magamp feedback control operation. The analysis reveals a pole-shifting phenomenon inherent in the type-A loop transfer function. A procedure for calculating the gain and open-loop poles in the control loop of each reset circuit is given. The procedure also shows how to compensate the error amplifier for stable operation. The detailed example of a 50-kHz magamp is given; however, the validity of the model has been demonstrated experimentally at 100 kHz. With a factor of two included in the Faraday's law block, the model describes loop behavior for a magamp with two saturable reactors for symmetrical topology.

[128] E. Muljadi, T. A. Lipo, and D. W. Novotny, "Power factor enhancement of induction machines by means of solid-state excitation," IEEE Transactions on Power Electronics, vol. 4, no. 4, pp. 409-418, 1989.

A novel concept for power correction of induction machines is introduced that employs an auxiliary three-phase stator winding together with a pulse-width-modulated (PWM) inverter to supply excitation power to the machine. When the PWM inverter is modeled as an equivalent capacitor, it is shown that two values of capacitance will yield unity power factor at a given operating condition. The effect of machine parameters on the critical value of capacitance is examined. A control algorithm to ensure unity power factor at the terminals of the main stator windings is presented, and its satisfactory operation is verified by means of a detailed analog computer simulation.

[129] H. Matsuo, F. Kurokawa, and K. Higashi, "Dynamic characteristics of the digitally controlled dc-dc converter," IEEE Transactions on Power Electronics, vol. 4, no. 4, pp. 419-426, 1989.

The dynamic characteristics of the digitally controlled DC-DC converter are analyzed theoretically and experimentally. The stability condition and the indicial response for the step changes of the input voltage and the load are defined as a function of the circuit parameters and variables of the digital control circuit and the power stage. The optimal proportional-integral-derivative (PID) coefficients of the digital control circuit are examined.

[130] F. D. Tan and R. S. Ramshaw, "Instabilities of a boost converter system under large parameter variations," IEEE Transactions on Power Electronics, vol. 4, no. 4, pp. 442-449, 1989.

The instabilities of the boost converter system caused by large variations of system parameters are explored using multiple-parameter, bifurcation-theory-oriented approaches. It is revealed that, depending on the eigenvalues of the Jacobian of the system, both static bifurcation (jump phenomenon) and dynamic bifurcation (onset of limit cycles) can occur at critical points. The stability conditions for both precritical and postcritical behavior of the system have been obtained and verified experimentally.

[131] G.-H. Choe and M.-H. Park, "Analysis and control of active power filter with optimized injection," IEEE Transactions on Power Electronics, vol. 4, no. 4, pp. 427-433, 1989.

An active filter that removes harmonics from the AC line by the injection of pulse-width-modulated (PWM) controlled currents is described. These compensating currents are optimized for the removal of all harmonic components up to a specified order using a filter that requires no supply other than the line to which it is connected. The required bidirectional power flow in the filter is achieved by establishing an internal inductor current within upper and lower limits by a purely fundamental current flow into the filter from the line. The performance characteristics of the proposed method are investigated by analysis and simulation. Experimental results from a microcomputer-controlled model establish the validity of the approach.

[132] R. J. King, "Fourier analysis for a fast simulation algorithm," IEEE Transactions on Power Electronics, vol. 4, no. 4, pp. 434-441, 1989.

A powerful discrete modeling approach to the simulation of a switching converter that has appeared in the power electronics literature over the last several years is briefly reviewed, and some desirable traits for its matrix exponential subroutine are discussed. The key result is a systematic and generic Fourier analysis that operates on the steady-state solution as provided by a discrete model. The Fourier analysis algorithm was tested on a phase-controlled parallel-loaded resonant converter which is useful as a fixed-frequency low-distortion AC source. Three verifications of the algorithm were made: a phasor analysis, an alternate closed-form analysis directed specifically to the problem at hand, and an analysis using experimental data. The performance of the algorithm was good for the case considered.

[133] W. A. Tabisz and F. C. Y. Lee, "Zero-voltage-switching multiresonant technique - a novel approach to improve performance of high-frequency quasi-resonant converters," IEEE Transactions on Power Electronics, vol. 4, no. 4, pp. 450-458, 1989.

A novel multiresonant switch concept is proposed to overcome the limitations of high-frequency quasi-resonant converters. A novel family of zero-voltage-switching (ZVS) multiresonant converters is generated. The unique arrangement of the multiresonant network results in absorption of all major parasitic components in the resonant circuit, including transistor output capacitance, diode junction capacitance, and transformer leakage inductance. This allows the new converters to provide favorable switching conditions for all semiconductors devices. Experimental results show that AVS multiresonant converters are superior to ZVS quasi-resonant converters due to their reduced transistor voltage stress and improved load range and stability.

[134] P. Pillay and R. Krishnan, "Control characteristics and speed controller design for a high performance permanent magnet synchronous motor drive," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 151-159, 1989.

The theory of vector control is applied to the nonlinear model of a permanent magnet synchronous motor to develop a linear model for controller design purposes. The operation and relevant mathematics of a pseudo-derivative feedback controller are presented. Controller designs for three different speeds are then considered, and a comparative evaluation is made on the basis of their large- and small-signal behavior. In order to test the large-signal response, the detailed nonlinear model of the machine and a real-time model of the inverter switches are used. Results indicate that a critically damped design done so as to ensure that all control and power signals never saturate gives an extremely poor result. Much better small- and large-signal responses are achieved by avoiding this constraint and using Zener diodes instead to limit the commanded input into the inverter. Two designs using this technique are presented, an underdamped design with low speed overshoot and an overdamped design with no speed overshoot. The response of the underdamped design was much quicker than that of the overdamped. However the overdamped design has application when speed overshoot is intolerable.

[135] M. M. Jovanovic and F. C. Y. Lee, "Dc analysis of half-bridge zero-voltage-switched multiresonant converter," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 160-171, 1989.

A complete DC analysis of the half-bridge zero-voltage-switched multiresonant converter is presented. The analysis reveals four different modes of operation. THe existence of the modes has been verified experimentally. A computer algorithm is developed for calculating the complete DC voltage-conversion-ratio characteristics encompassing all four modes of operation. The DC characteristics enable the design of the converter to be optimized. The optimization is performed by selecting the resonant components and the turns ratio of the transformer. The computer algorithm can be easily adapted for the analysis of the small-signal properties of the half-bridge multiresonant converter.

[136] T. J. Sobczyk and B. L. Sapinski, "Analysis of phase-controlled converters for induction motors," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 172-181, 1989.

A phase-controlled converter for induction motors is analyzed, using a representation of semiconductor switching devices as two-state resistances. The steady state of symmetrically controlled converters (when the states of the semiconductor switching devices change periodically) is considered, and symmetrical components of the motor phase currents are used. This allows classical equivalent circuits of the induction motor to be used. As a result of the analysis the Fourier spectrum of the motor phase currents and electromagnetic torque is determined. An example that shows the application of the relations presented here is given.

[137] P. T. Krein, J. Bentsman, R. M. Bass, and B. L. Lesieutre, "On the use of averaging for the analysis of power electronic systems," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 182-190, 1989.

Averaging theory as a rigorous framework for evaluating, refining, and extending heuristic averaged models now used in power electronics is introduced. It is shown that averaging theory provides direct techniques for recovering oscillatory effects such as ripple from the averaged model. As an application of the theory, examples of the analysis of simple DC-DC converters are presented.

[138] K. E. Addoweesh and A. L. Mohamadein, "Microprocessor based harmonic elimination in chopper type ac voltage regulators," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 191-200, 1989.

A control strategy for firing instances in pulse-width-modulated (PWM) AC voltage regulators is presented. In this type of regulator, output voltage is controlled by varying the on/off time ratios of a series-controlled switch. Using a microprocessor as a controller makes it possible to vary firing instances at will according to a predetermined timing regime. One of these regimes, proposed here, involves adjusting firing instances so that selected dominant lower-order harmonics can be eliminated. This in turn leads to improved system power factor and efficiency. The theoretical principles used in evaluating firing instances are described, and experimental results verifying the analysis are presented.

[139] C. T. Rim and G. H. Cho, "Phasor transformation and its application to the dc/ac analyses of frequency phase-controlled series resonant converters (src)," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 201-211, 1989.

A novel modeling technique based on phasor transformation that provides a unified model of series resonant converters (SRCs) is proposed. The approach gives explicit and simple equations that provide fruitful physical insight. When the switching frequency deviates from the resonant frequency, a first-order SRC model is obtained, and in the case of resonance a second-order model is obtained. It is shown that the frequency band of the second-order model is very narrow in practice. The time constant, small-signal gains, and system order are highly dependent on the switching frequency, load resistor, and output capacitor.

[140] M. Marchesoni, M. Mazzucchelli, and S. Tenconi, "Nonconventional power converter for plasma stabilization," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 212-219, 1989.

The authors present the design and control of a nonconventional converter with a peak power of 3.6 MVA and a bandwidth ranging from DC values up to 10 kHz for nuclear-fusion experiments. The novel control technique is based on a comparison between the current reference and the load current, through a hysteresis comparator system. The required voltage waveforms have been obtained in two specified frequency ranges, with a strictly unified control over the whole bandwidth range. The conditions on the maximum phase shift and the maximum switching frequency required have all been fulfilled. Excellent results obtained by digital simulation confirm the validity of the proposed control scheme. The converter described here has been studied and designed for an experiment that has recently been proposed within the framework of the JET (Joint European Torus) project.

[141] M. H. Kheraluwala and D. M. Divan, "Delta modulation strategies for resonant link inverters," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 220-228, 1989.

The suitability of delta modulation strategies for resonant link inverters is explored in detail. The control and spectral characteristics of various delta modulators are examined in an effort to develop a model for the same. The more fundamental question of comparing delta modulation systems with conventional pulse-width-modulated (PWM) systems, given similar devices, is addressed, and it is shown that the former provides a viable high-performance alternative. As the resonant DC link topology allows at least an order of magnitude increase in the switching frequency, ΣΔM systems using a given family of devices are capable of better spectral response than a conventional PWM inverter.

[142] M. M. Jovanovic, W. A. Tabisz, and F. C. Y. Lee, "High-frequency off-line power conversion using zero-voltage-switching quasi-resonant and multiresonant techniques," IEEE Transactions on Power Electronics, vol. 4, no. 4, pp. 459-469, 1989.

The characteristics and limitations of the half-bridge zero-voltage-switched (ZVS) quasi-resonant converters (QRCs) are described. A novel multiresonant concept is proposed for the half-bridge topology to improve the ZVS QRC's load range. Experimental results for 300-V, 75-W zero-voltage-switched quasi-resonant and multiresonant converters operating in the frequency range from 2 MHz to 8 MHz are presented.

[143] B. Ray and T. A. Stuart, "Analysis of n schwarz inverters driving a common ac bus," IEEE Transactions on Power Electronics, vol. 4, no. 4, pp. 470-477, 1989.

It is noted that electric power systems for future spacecraft may need distribution networks with multiple inputs and outputs. It is suggested that one way of achieving such a system is to connect Schwartz inverters in parallel to drive a common AC bus. A steady-state model is derived to calculate certain variables of interest and to predict how these inverters will share the load. Experimental results verify the feasibility of this approach and indicate reasonable agreement with the calculations.

[144] B. Ray and T. A. Stuart, "Cascaded schwarz converter for high frequency power distribution," IEEE Transactions on Power Electronics, vol. 4, no. 4, pp. 478-485, 1989.

AC distribution networks operating at 20 kHz are being considered for future spacecraft. These systems offer important reductions in size and weight and are easier to protect than DC systems at high power levels. It is suggested that two Schwarz converters in cascade provide a very reliable 20-kHz source that features zero-current commutation, constant frequency, and fault-tolerant operation. Equations for the steady-state performance are derived, and graphical results can be plotted in a convenient manner. A 900-W version has been built and successfully tested under no-load, full-load, and short-circuit conditions.

[145] L.-H. Hoang and L. A. Dessaint, "Adaptive current control scheme for pwm synchronous motor drives: Analysis and simulation," IEEE Transactions on Power Electronics, vol. 4, no. 4, pp. 486-495, 1989.

Two schemes for controlling the motor currents in PWM (pulse-width-modulated) inverters in synchronous motor drives are considered: hysteresis control and predictive control. It is pointed out that the system static and dynamic performance can be improved by selecting the control mode in an adaptive manner according to the operating conditions. In steady state, the predictive mode is selected to reduce current ripple and to obtain stable switching frequency. During large transients, such as during starting or load variations, the hysteresis mode is selected to provide fast response. The performance of the proposed control scheme has been studied by simulation, and the results agree well with the prediction. This adaptive control scheme can be implemented using a high-performance 16-bit microcontroller supported by a mathematical coprocessor.

[146] B. T. Ooi and X. Wang, "Voltage angle lock loop control of the boost type pwm converter for hvdc application," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 229-235, 1989.

The advent of high-power, high-frequency, solid-state switches with fast gate turn-off capabilities suggests that pulse-width-modulated (PWM) techniques can soon be introduced into HVDC (high-voltage direct-current) applications. A boost-type PWM converter with voltage angle lock control that is tailored to the utility environment is described. Experimental test results for 1-kVA models show that the advantages are substantial.

[147] F. Chen and X. S. Cai, "Design of feedback control laws for switching regulators based on the bilinear large signal model," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 236-240, 1989.

A method for the design of a linear feedback control law for switching regulators based on the bilinear large-signal model is presented. The resulting system guarantees a satisfactory stability region in the state space, and meets the requirements of large damping on transient responses with small feedback control energy. Large-signal transient responses are simulated and compared with the results obtained by R. W. Erickson et al. (1985). The proposed method is well suited for converter topologies with more than two state variables.

[148] T. Charanasomboon, M. J. Devaney, and R. G. Hoft, "Single switch dual output dc-dc converter performance," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 241-245, 1989.

The performance of the single-switch dual-output DC-DC converter is evaluated. This converter regulates two independent DC outputs supplied from a single DC voltage source using a power semiconductor switch. Two discrete proportional feedback control loops regulate the duration of on switching and off switching. The duty cycle of the switch controls one output voltage, supplied from a low-pass filter, while the switching frequency regulates the other output voltage, supplied from a higher-frequency bandpass filter. The control algorithm is implemented with an Intel 8096 microcontroller. The experimental data demonstrate the actual circuit performance and confirm the simulation results. Both experiments and simulation show that an increase in the load current on the 12-V output results in an increase in the duty cycle, whereas an increase in the load current on the 5-V output results in a change in the switching frequency. The experimental prototype demonstrates operation over a load current range from about 40% to 100% with a &plusmn25% variation in the 24-V input. Full load currents are 12 A and 2.5 A on the 12-V and 5-V outputs, respectively. The switching frequency ranged from approximately 29 kHz to 264 kHz, and the duty cycle ranged from 0.35 to 0.72.

[149] G.-H. Choe, A. K. Wallace, and M.-H. Park, "Improved pwm technique for ac choppers," IEEE Transactions on Power Electronics, vol. 4, no. 4, pp. 496-505, 1989.

A novel pulse-width-modulated (PWM) control technique for AC choppers is proposed that has the advantages of enabling linear control of the fundamental component of the output voltage and complete elimination of its harmonics up to a specified order. Theoretical comparisons are made with other basic PWM techniques, and the computed performance indicates the superiority of the present method. The carrier wave required for the new technique is easily determined as a modification of a basic triangular wave that enables the beneficial features to be obtained over the full range of chopper operation and can be implemented by the storage of relatively simple control equations. An experiment has verified the feasibility of the method as applied to the control of a single-phase automatic voltage regulator. In the experiment the modified triangular carrier wave is used to generate the required PWM switching function. Good agreement is obtained between the calculated and experimental results.

[150] T. Nishimura, M. Nakaoka, and T. Maruhashi, "Reduction of vibration and acoustic noise in induction motor driven by three phase pwm ac chopper using static induction transistors," IEEE Transactions on Power Electronics, vol. 4, no. 3, pp. 313-318, 1989.

A three-phase pulse-width-modulated (PWM) chopper that uses a static induction transistor (SIT) to chop the three-phase AC voltage with a 20-kHz carrier frequency and control an induction motor is proposed. Harmonic components in the voltage and current waveforms do not appear in the audio frequency band with this method. When each terminal of the motor is connected to a 4-μF capacitor, the terminal voltage and line current waveforms are almost sinusoidal. The motor speed is controlled by changing the on-time width of the gate signal. The power spectrum of the chopper-driven motor driven by the chopper is calculated using a fast Fourier transform and measured. The results are used to reduce vibration and acoustic noise in the motor, which is confirmed by measurement.

[151] A. M. Trzynadlowski, "Nonsinusoidal modulating functions for three-phase inverters," IEEE Transactions on Power Electronics, vol. 4, no. 3, pp. 331-338, 1989.

A major class of pulse-width-modulation (PWM) techniques for power inverters is distinguished by the use of reference, or modulating, functions. The characteristics of these techniques can be improved considerably by employing nonsinusoidal modulating functions in place of the usual sinusoidal function. Two kinds of modulating functions are considered, and their impact on the inverter performance is analyzed. Both of them result in a significantly increased fundamental and reduced harmonic content of the inverter output voltage. Implementation of the optimal nonsinusoidal modulating functions is illustrated by their application in the incremental PWM method, but the idea can be extended to a broad class of other PWM techniques.

[152] A. Ioinovici, "New computer-aided approach to the analysis of cuk converter by using the alternor equations," IEEE Transactions on Power Electronics, vol. 4, no. 3, pp. 319-330, 1989.

A novel approach to the computation of the transient and steady-state response of power electronic switching converters is presented. The solution exhibits precision and reflects the continuous character of the converter waveforms. The key to the approach is the extraction of the switching elements (transistors, or transistor and diode, operated as synchronous switches) in a time-varying two-port called an alternor. The remaining part of the converter is linear and time-invariant; it can be described, in the complex frequency domain, by a system of modified nodal equations. The constitutive equations of the alternor are added, providing a global model of the cyclically switching circuit in the s-domain. The converter is analyzed using the Laplace transform. The modified nodal equations of the converter are solved, and the inverse Laplace transform of their solutions is found. The time-domain solutions together with boundary conditions for cyclical operation of the converter are used for the computer-aided calculation of the transient and steady-state response. The method is applied to a coupled-inductor Cuk converter operating in a continuous conduction mode in which the transient state is due to a step-in-line input voltage.

[153] M. M. Jovanovic and F. C. Y. Lee, "Dc characteristics and stability of push-pull and bridge-type zero-current-switched quasi-resonant converter," IEEE Transactions on Power Electronics, vol. 4, no. 3, pp. 339-347, 1989.

In the buck-derived, push-pull, and bridge-type topologies the output inductor current during the switched-off interval can free-wheel either through the shorted secondaries of the transformer or through a separate free-wheeling diode (FWD). It is shown that the former method results in highly nonlinear DC voltage-conversion-ratio characteristics for zero-current-switched quasi-resonant converters operating in the half-wave mode. As a result the incremental gain of the power stage of these converters varies with input voltage and load over an extremely wide range, so that it is not possible to achieve stable feedback control with high loop gains using conventional compensation techniques. It is shown that the addition of a FWD not only linearizes the DC characteristics but also reduces current and voltage stresses on semiconductor devices and improves efficiency.

[154] J. C. Bendien and J. Geuenich, "On the behavior of a current fed synchronous machine drive without dc-link inductance," IEEE Transactions on Power Electronics, vol. 5, no. 2, pp. 246-251, 1989.

A drive system with synchronous machine and machine-commutated thyristor-inverter is discussed. The current source of this type of drive is realized by a fast switching transistor chopper, and the current is smoothed by the machine reactance and, atypically, by a choke in the DC link. It is shown that operation without link inductance affects the margin angle of the inverter. Hence, the reactive power of the machine has to be increased considerably. To overcome this disadvantage, a special method of control is presented, investigated, and verified by experimental results.

[155] F. C. Zach, K. H. Kaiser, and L. J. Faschang, "New mcmurray-type inverter with asymmetric scr's," IEEE Transactions on Power Electronics, no. 272-278, 1989.

The standard, simple McMurray inverter is improved in three steps. The first step, adding recharging and energy feedback pulses, keeps the inverter operating satisfactorily at low loads and also limits overcharging of the commutation capacitor. The second step involves replacing the standard LC ringing circuit (for commutation) by a long line which has to be approximated by concentrated elements. This changes the sinusoidal commutation current pulse to a rectangular shape and eliminates wasted time due to the rise of the sine wave in the standard circuit. The system therefore needs only 70% of the commutation time required for the standard system, so that about 1.4 times higher pulse frequencies can be realized. The third step, using newly developed asymmetric silicon-controlled rectifiers (ASCRs), is made possible by the structure of the improved inverter, where diodes are used in antiparallel to the main thyristors. The ASCRs require about 1/3 of the turn-off time of conventional thyristors. Altogether, inverter output frequencies of up to 1.4×3=4.2 times the frequencies achievable with conventional means were obtained.

[156] A. W. Kelley and W. R. Owens, "Connectorless power supply for an aircraft-passenger entertainment system," IEEE Transactions on Power Electronics, vol. 4, no. 3, pp. 348-354, 1989.

The authors consider an entertainment system that places small video entertainment sets at every seat for use by each passenger. Each set in the system must be provided with audio and video programming and the electrical power necessary to operate the set. Distribution of programming and power to the sets with a connector for each set would cause reliability and maintenance problems and hinder timely cabin reconfiguration. The entertainment sets can receive audio and video signals through radio-frequency transmission, but distributing power to the sets without using connectors requires a novel approach. The analysis, design, and construction of a prototype connectorless power supply that inductively couples power to the entertainment sets across an air gap is described. An equivalent-circuit model of the supply is developed, and laboratory measurements performed on the prototype are discussed. The prototype unit is shown to be a practical implementation that meets all design requirements.

[157] N. H. Malik, "Analysis and performance characteristics of three-phase, thyrode ac voltage controllers," IEEE Transactions on Power Electronics, vol. 4, no. 3, pp. 355-361, 1989.

A generalized approach based on numerical evaluation of the Fourier coefficients is used to determine the performance of three-phase phase-controlled thyrode AC voltage controllers. Balanced resistive and inductive loads of different power factors are considered. Various electrical properties are computed and compared graphically for different circuit configurations. It is found that although the branch-controlled delta-connected load gives the highest distortion and power factors, it offers limited control of input power. The line-controlled star-connected circuit offers full range of power control, a simple control scheme over a wider range of firing angle retardation, and good distortion and power factors. For applications where even harmonics can be tolerated in the line currents, such a controller has superior performance characteristics compared to that of the conventional thyristor voltage controller of similar configuration.

[158] C. G. Steyn, "Analysis and optimization of regenerative linear snubbers," IEEE Transactions on Power Electronics, vol. 4, no. 3, pp. 362-370, 1989.

The regenerative linear turn-on and turn-off snubbers are analyzed and optimized independently. The optimization for fixed supply voltage and load current is done in terms of minimum total energy losses in the power electronic circuit during switching. It is shown that the dissipative snubber, which up to now has been the only optimized snubber, becomes a special case of this general linear snubber. Equations describing the most important parameters are presented in normalized form in tables, and some energy results are presented in graphical form. Calculated results show that if the regenerative snubber's recovery efficiency is higher than 67%, the abovementioned optimum snubber can be used to perform snubbing action during the complete fall-time transition.

[159] M. I. Castro Simas, M. Simoes Piedade, and J. Costa Freire, "Experimental characterization of power vdmos transistors in commutation and a derived model for computer-aided design," IEEE Transactions on Power Electronics, vol. 4, no. 3, pp. 371-378, 1989.

The authors present experimental method for the characterization of MOS power switching transistors that does not involve technological parameters that are not available to designers. The method is based on the time-domain analysis of the commutation performance of the transistor when constant currents are injected into its terminals. The analysis of the time-domain waveforms and the knowledge of the internal structure of the MOS devices are sufficient for the evaluation of the transistor capacitances. It is then possible to introduce a simple large-signal model for power MOSFETs that is particularly well suited to the analysis of circuits using the MOS transistor in commutation (e.g., switching power converters or high-efficiency power amplifiers). The authors also present the model implementation in the Spice 2 program. Comparison between results obtained experimentally and by computer simulation for several circuits confirms the accuracy of the proposed method.

[160] A. F. Goldberg, J. G. Kassakian, and M. F. Schlecht, "Finite-element analysis of copper loss in 1-10-mhz transformers," IEEE Transactions on Power Electronics, no. 157-167, 1989.

Issues related to the copper loss in the planar windings of 1-1-MHz power transformers are discussed. The relationship between current distribution, copper loss, and core geometry is investigated with the aid of finite-element analysis. Magnetizing current proximity effects are shown to cause excessive copper loss in a simple sandwich transformer, a structure formed by sandwiching the planar winding between two plates of magnetic material. Three alternative transformer structures that reduce this problem are compared. These alternative structures are: the cofired transformer, the slotted gapped transformer, and the slotted ungapped transformer. It is concluded that a slotted transformer design should be used if the magnetizing current is relatively large. Both a slotted gapped and a slotted ungapped structure give comparable results, although the ungapped design relies strongly on the exact permeability of the material and may suffer from higher core losses because all of the energy is stored in the magnetic material, rather than in an air gap. In either case, the depth of the slot should be about 40% of its width.

[161] R. Rangan, D. Y. Chen, J. Yang, and J. Lee, "Application of insulated gate bipolar transistor to zero-current switching converters," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 2-7, 1989.

The problems associated with insulated-gate bipolar transistor (IGBT) devices in PWM converters, such as turn-off current tailing and turn-off latching, are largely avoided in zero-current switching resonant converters. Phenomena induced by dv/dt, such as the power losses and latching, are identified as the predominant problems in using IGBT devices for very-high-frequency resonant operations. The discussion and the verification of the results presented are focused on buck-type converters in the zero-current switching family.

[162] D. M. Divan, "Diodes as pseudo-active elements in high-frequency dc/dc converters," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 8-14, 1989.

A novel approach to realizing zero-voltage switching in high-frequency DC/DC converters is presented. Utilizing the parasitic associated with the diode stored charge, it is shown that the diode reverse current established for charge removal can be used advantageously to accomplish soft switching. The entire family of single-transistor DC/DC converters can be realized using the technique. The converter topologies are seen to differ from their hard-switched counterparts only by the presence of a resonant capacitor. It is also shown that device and component stresses are moderate as compared to existing quasi-resonant and resonant techniques. Converter analysis is rather complex as a result of the dominant diode nonlinearities, and no closed-form expressions are possible. Converter transfer characteristics are obtained through simulation, and operating limits are analytically obtained. The concept is validated by experimental results using buck-type converters rated at approximately 100 W and operating at frequencies around 1 MHz.

[163] V. Vorperian, "Approximate small-signal analysis of the series and the parallel resonant converters," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 15-24, 1989.

Approximate transfer functions of series and parallel resonant converters are given which are in good agreement with the results of exact analysis as well as the results of experiments. It is shown that the dominant behavior of these transfer functions is determined by the output low-pass filter modified by the internal impedance of the converter. The high-frequency behavior, on the other hand, is given by a second-order response whose frequency is at the difference between the resonant and the switching frequencies and whose Q is the original resonant Q modifed by the internal impedance of the converter.

[164] G. K. Schoneman and D. M. Mitchell, "Output impedance considerations for switching regulators with current-injected control," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 25-35, 1989.

The output impedance of current-injection-controlled (CIC) buck regulators can be significantly reduced by deriving the current control signal from the output capacitor instead of the inductor. This technique is shown to be mathematically equivalent to CIC with load-current feedforward. Performance comparisons with normally implemented CIC and voltage control are given.

[165] R. D. Middlebrook, "Modeling current-programmed buck and boost regulators," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 36-52, 1989.

A general small-signal model for current-programmed switching power stages is used for design-oriented analysis of a 150-W buck regulator and a 280-W boost regulator. The model, into which the current-programming minor feedback loop is absorbed, exposes the desired tendency towards 'constant' output current. The regulator voltage loop remains the only explicit feedback loop, allowing the regulator closed-loop properties to be easily obtained from those of the open-loop current-programmed power stage. The design-oriented analytic results allow easy inference of the effects of element changes on the regulator performance functions. Results are obtained for the regulator line-to-output transfer function (audio susceptibility) and output impedance.

[166] L. D. Salazar and P. D. Ziogas, "Single-ended smr converter topology with optimized switching characteristics," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 53-63, 1989.

The analysis and design of an improved single-ended switched-mode rectifier (SMR) converter topology is presented. The novel feature of this topology is a nondissipative LC-type subcircuit which provides transformer flux balancing and improves converter efficiency. This is achieved by minimizing switching losses and by returning the energy stored in the transformer leakage and circuit stray inductances to the source and the load. Theoretical predictions and SMR converter design procedures are verified experimentally on a 1-kW 20-kHz prototype circuit.

[167] F. C. Zach, "Comparison of voltage and current spectra using optimized forms of inverter pulsewidth modulation," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 64-72, 1989.

Modern electrical drive technology tends toward application of alternating current machines (especially induction motors) for variable-speed drives. This is general requires providing of voltages with adjustable frequency and amplitude. This is achieved most advantageously with pulsewidth-modulated (PWM) inverters. After an overview of the basic concepts, the different optimization criteria important for practical applications are discussed. Of special interest are efficiency optimization and torque-ripple optimization These two optimization criteria are treated in detail. Computer simulations for both cases and experimental results for efficiency optimization are presented and compared. Special attention is given to the various switching laws generating the PWM for the inverters and to the voltage and current spectra associated with them. The differences in drive dynamics optimization are also discussed.

[168] J. Zhang and T. H. Barton, "Microprocessor-based primary current control for a cage induction motor drive," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 73-82, 1989.

A novel approach for primary current vector control of a current-source inverter induction motor (CSI-IM) drive with an improved estimation of slip angular frequency is described. Accurate digital control of the current vector orientation is achieved. Advanced software control logic provides the drive with rapid speed reversal and regenerative braking. A simple variable-structure current controller improves the system stability and robustness in performance. System large-signal operation and optimization are briefly discussed. Experimental results verify system development and design.

[169] G. B. Joung, C. T. Rim, and G. H. Cho, "Integral cycle mode control of the series resonant converter," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 83-91, 1989.

A control method for the series resonant converter (SRC) in which the device switching instants are always synchronized to the zero-crossing points of the resonant current is proposed. Output voltage is controlled by proper selection of the switch modes by varying the duty ratio of the powering mode and free resonant mode. Each switch mode is analyzed and the DC transfer function is obtained. It is also shown that the simulation results coincide well with the practical case. The SRC using the proposed control scheme shows many advantages, such as low current-switching stress, low switching loss, low electromagnetic interference, high input power factor, and wide control range. Some of these characteristics are verified experimentally.

[170] J. Holtz and H.-J. Klein, "Propagation of harmonic currents generated by inverter-fed locomotives in the distributed overhead supply system," IEEE Transactions on Power Electronics, no. 168-174, 1989.

Pulse-width-modulated converter-fed locomotives generate current harmonics that give rise to traveling waves in the overhead supply system. The waves are partially reflected at the feeding substations, causing parallel and series resonances at various discrete frequencies. An investigation based on the wave propagation approach demonstrates the influence of the track topography and the varying position of locomotives within the track. The distribution of harmonic currents in the overhead supply system is evaluated and discussed. These currents are shown to be much higher in certain locations of the railway track than the harmonic current injected by a locomotive. They may also appear at distant track locations. The natural resonances in the overhead supply system determine the intensity of electromagnetic interference with the track-side communication lines.

[171] H. Matsuo, F. Kurokawa, and T. Takeda, "Analysis of the dynamic characteristics in the overcurrent limited mode of the dc-dc converter," IEEE Transactions on Power Electronics, no. 175-180, 1989.

The steady-state and dynamic characteristics in the overcurrent-limited mode of a DC-DC converter are analyzed theoretically and experimentally. The circuit conditions are defined for foldback current limiting, constant current, and voltage drooping characteristics, which are realized when the DC voltage gain of the overcurrent limiting control loop is larger than, equal to, and less than unity, respectively. It is shown that the stability in the overcurrent-limited mode, as well as the transient response from the load point in the constant voltage-regulated mode to that in the current-limited mode, can be improved by using a relatively large DC voltage gain and by approximately adjusting the rate time and reset time in the derivative and integral compensators, respectively.

[172] D. M. Mitchell and G. K. Schoneman, "On the selection of control-law coefficients for multiloop pwm switching regulators," IEEE Transactions on Power Electronics, no. 181-186, 1989.

An analytical investigation was performed to ascertain the explicit effects of the state-variable feedback control-law coefficients and the source variable feed-forward control-law coefficients on the stability and performance in linearized multiloop (pulse-width modulated) switching regulators. Detailed results are presented for input impedance, output current susceptibility, input voltage susceptibility and output impedance of the basic buck, boost, and buck-boost regulators. General relationships are derived for the feed-forward control-law coefficients to minimize input voltage susceptibility and the output impedance of the multiloop buck regulator. Relationships for all three regulators based on other performance measures such as output current susceptibility can be derived using the results presented. Simplified results are given for multiloop switching regulators with a conventionally implemented current loop and with a value of inductance several times greater than critical.

[173] K. Muraoka, Y. Kawamura, Y. Ohtsubo, S. Sugawara, T. Tamamushi, and J.-i. Nishizawa, "Characteristics of the high-speed si thyristor and its application to the 60-khz 100-kw high-efficiency inverter," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 92-100, 1989.

The authors describe fabrication results for the 1200-V, 300-A class of the single-buried-gate, n-buffer free and anode-emitter-shorted, normally-on-type, medium-power, very low-loss, high-speed SI thyristor. This class of thyristors has a relatively thinner n-type high resistivity that is larger than that of the 2500-V 300-A class of SI thyristors. The characteristics of the fabricated device were investigated to obtain data for the improvement of the turn-off switching performance of the buried-gate SI thyristor for use as a power switch.

[174] A. Alesina and M. G. B. Venturini, "Analysis and design of optimum-amplitude nine-switch direct ac-ac converters," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 101-112, 1989.

The maximum input-output transformer ratio, or output voltage ability, of direct AC-AC pulse-width-modulated converters is explored. An intrinsic limit, independent of the control algorithm, is found. A suitable novel converter control algorithm is discussed which achieves such maximum output amplitude ability and displays some interesting features. Finally, the opportunity to implement AC-AC converter control with the use of feedback techniques is considered, and a feedback-based control algorithm for the converter is proposed.

[175] A. F. Goldberg, J. G. Kassakian, and M. F. Schlecht, "Issues related to 1-10-mhz transformer design," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 113-123, 1989.

Issues related to the design of high-frequency transformers are discussed. An analysis of skin and proximity effects in the conductors and measurements of permeability and hysteresis loss in the magnetic material are combined in a computer-assisted study of the relationships between size, efficiency, and frequency. Experimental data are presented for a prototype transformer.

[176] M. K. Kazimierczuk and X. T. Bui, "Class e dc/dc converters with an inductive impedance inverter," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 124-135, 1989.

The analysis, design equations, and experimental verification are presented for a class E DC/DC switching-mode high-efficiency resonant DC/DC converter with a transformer center-tapped rectifier. The analysis is performed at a constant current through the DC-feed choke and using the high Q₁ assumption (Q₁ >= 5). The converter can operate under safe conditions for load resistances ranging from a full load to an open circuit. This feature has been obtained by using an inductive impedance inverter. The results of the analysis are then generalized for the entire family of class E DC/DC converters. Experimental results show good agreement with the theoretical predictions. The measured total efficiency was 89% at 1 MHz with 15-W output power. A narrowband FM regulation (δf/f = 12%) of the DC output voltage was achieved as the load was varied from a minimum resistance (full load) to an open circuit.

[177] M. M. Jovanovic, D. C. Hopkins, and F. C. Y. Lee, "Evaluation and design of megahertz-frequency off-line zero-current-switched quasi-resonant converters," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 136-146, 1989.

A performance comparison of flyback, forward, and half-bridge zero-current-switched quasi-resonant converter topologies for high-frequency offline applications is presented. It is shown that the half-bridge topology with secondary side resonance operating in half-wave mode is most suitable. A complete design procedure for the half-bridge power stage and the voltage-feedback control is presented together with experimental results for a 300-V DC hybridized converter which operates with conversion frequencies from 400 kHz to 2 MHz and delivers 1.5-16 A at 5 V DC.

[178] D. C. Hopkins, M. M. Jovanovic, F. C. Y. Lee, and F. W. Stephenson, "Hybridized off-line 2-mhz zero-current-switched quasi-resonant converter," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 147-154, 1989.

Thick-film hybrid technology is used to develop a half-bridge, half-wave, zero-current-switched quasi-resonant converter for 300-V DC offline application. With a conversion frequency of 2 MHz the converter delivers 80 W at 78% efficiency with a power density, excluding heat sink, of 21 W/in³. The operation and detailed electrical and hybrid design of the circuit are described. Also described is a 2-MHz hybridized gate drive.

[179] H. M. Turanli, R. W. Menzies, and D. A. Woodford, "Forced commutated inverter as a small series tap on a dc line," IEEE Transactions on Power Electronics, no. 187-193, 1989.

A forced commutated inverter used for tapping energy to a remote load from a DC line running through a rural area is described, and the results of a study conducted on Manitoba Hydro's Electromagnetic Transients Program are presented. It is shown that a passive load requiring real and reactive power can easily be supplied. The tap itself is capable of responding quickly to changes of load without a communication link to the main converter terminals. The tap is able to recover easily from all anticipated faults and disturbances taking place in its own system as well as at the main converter terminals. It is noted that the series inverter tap with forced communication is not as sensitive to AC side disturbances as was the multiterminal system with a small parallel tap.

[180] W. A. Tabisz, P. M. Gradzki, and F. C. Y. Lee, "Zero-voltage-switched quasi-resonant buck and flyback converters - experimental results at 10 mhz," IEEE Transactions on Power Electronics, no. 194-204, 1989.

Experimental results are presented for buck and flyback zero-voltage-switched (ZVS) quasi-resonant converters (QRCs) operating above 5 MHz. A design procedure for a buck ZVS QRC is proposed that minimizes voltage stress to the power MOSFET transistor while maintaining zero voltage switching for specified ranges of input voltage and load resistance. A quasi-resonant gate drive sceme is also proposed and implemented in a buck converter. The drive is simple and provides high switching speed. Power dissipation in the gate drive is substantially reduced due to the quasi-resonant operation. The ZVS QRC technique described is suitable for very-high-frequency operation due to its ability to reduce dynamic turn-on losses, Miller effect, dv/dt, and di/dt and can be applied in distributed onboard power supplies.

[181] V. Vorperian, R. Tymerski, and F. C. Y. Lee, "Equivalent circuit models for resonant and pwm switches," IEEE Transactions on Power Electronics, no. 205-214, 1989.

The nonlinear switching mechanism in pulsewidth-modulated (PWM) and quasi-resonant converters is that of a three-terminal switching device which consists only of an active and a passive switch. An equivalent circuit model of this switching device describing the perturbations in the average terminal voltages and current is obtained. Through the use of this circuit model the analysis of pulsewidth modulated and quasiresonant converters becomes analogous to transistor circuit analysis where the transistor is replaced by its equivalent circuit model. The conversion ratio characteristics of various resonant converters and their relationship to a single function, called the quasi-resonant function, is easily obtained using the circuit model for the three-terminal switching device. The small-signal response of quasi-resonant converters to perturbations in the switching frequency and input voltage is determined by replacing the three-terminal switching device by its small-signal equivalent circuit model.

[182] M. M. Jovanovic, F. C. Y. Lee, and D. Y. Chen, "Zero-current-switched off-line quasi-resonant converter with reduced frequency range: Analysis, design, and experimental results," IEEE Transactions on Power Electronics, no. 215-224, 1989.

A half-bridge zero-current-switched (ZCS) offline quasi-resonant converter (QCR) operating in full-wave mode is implemented to reduce the modulation frequency range due to load variations. The design and characteristics of the converter are described and compared with their half-wave counterpart in frequency range, component stress, and efficiency. An experimental converter which delivers output power from 10 to 100 W with a modulation frequency from 700 kHz to 1.4 MHz is presented. The converter showed superior transient response compared to the corresponding half-wave converter. The efficiency of the full-wave converter at full-load was several percent lower than that of the half-wave converter and decreases at a much faster rate as the output power decreases.

[183] R. Tymerski, V. Vorperian, F. C. Y. Lee, and W. T. Baumann, "Nonlinear modeling of the pwm switch," IEEE Transactions on Power Electronics, no. 225-233, 1989.

The nonlinearity due to the switching action in pulse-width-modulated (PWM) DC-to-DC converters, DC-to-AC inverters, or amplifiers and input-current-shaping AC-to-DC converters can often conveniently be confined to three-terminal structure referred to as the PWM switch. The PWM switch represents a static nonlinearity for which circuit models can easily be derived for frequencies harmonically related to the frequency of perturbation. Converter analysis can thus be approached in a way analogous to ordinary transistor circuit analysis whereby the nonlinear three-terminal device is replaced by its circuit model. A first-order approximation of the model results in th small-signal model.

[184] J. A. Asumadu and R. G. Hoft, "Microprocessor-based sinusoidal waveform synthesis using walsh and related orthogonal functions," IEEE Transactions on Power Electronics, no. 234-241, 1989.

A method is described of eliminating harmonics in a pulsewidth-modulated waveform using Walsh and related functions that substitute linear algebraic equations for the nonlinear equations required in Fourier-series harmonic elimination. A microprocessor can then be used to calculate the firing angles to cancel the unwanted harmonics. In an extension of the method, it is shown that a sine wave can be synthesized from a fixed-voltage DC supply by using a reasonable number of power electronic switches.

[185] A. K. Wallace and R. Spee, "Effects of motor parameters on the performance of brushless dc drives," IEEE Transactions on Power Electronics, vol. 5, no. 1, pp. 2-8, 1990.

A simulation model for predicting the transient performance of brushless DC drives is described. The model does not require assumptions of phase balance of either the power electronic converter or the motor, nor are idealized waveforms for the induced voltage or phase and mutual inductance terms necessary. The model is applied to drives for which neither equivalent-circuit nor d-q axis analyses are rigorously applicable. Test results establish the degree of correlation of the predictions with a practical example. The model is then used to conduct a sensitivity study that not only explores the degrees of model complexity necessary for adequate representation but also provides guidelines to system designers on the effects of certain practical configurations. The importance of the interaction of converter details, such as the pulse-width-modulated (PWM) technique, and motor parameters, such as the induced voltage waveform, is stressed in the approach considered.

[186] F.-Z. Peng, H. Akagi, and A. Nabae, "Study of active power filters using quad-series voltage-source pwm converters for harmonic compensation," IEEE Transactions on Power Electronics, vol. 5, no. 1, pp. 9-15, 1990.

An active power filter using quad-series voltage-source pulse-width-modulated (PWM) converters to suppress AC harmonics by injecting compensating currents into the AC system is described. The circuit used to calculate the compensating current references, the compensation characteristics, and the capability of the DC capacitor are discussed theoretically and experimentally. A control circuit for the DC capacitor voltage is proposed. The discussions focus on transient states, based on the instantaneous reactive power theory. A passive LC filter is designed to remove the switching voltage and current ripples caused by the PWM converters at the AC side. Some experimental results that illustrate the details of the study are shown.

[187] Y.-C. Liang and V. J. Gosbell, "Dc machine models for spice2 simulation," IEEE Transactions on Power Electronics, vol. 5, no. 1, pp. 16-20, 1990.

A four-level computer model is proposed for DC machine simulation using SPICE2 to meet different simulation requirements. The most complex model takes account of magnetic saturation, armature reaction, current dependence of winding circuit parameters, and eddy current effects. The models have been developed to enable designers to simulate the static and dynamic characteristics of a complete converter drive system including the DC machine more simply, practically, and reliably in one simulation run. Some simulations have been investigated to demonstrate the benefits of the SPICE2 machine models.

[188] P. G. Maranesi, L. Pinola, and V. Varoli, "Switched filter for the compensation of power processors," IEEE Transactions on Power Electronics, vol. 5, no. 3, pp. 253-259, 1990.

An analog-amplitude discrete-time recursive filter is proposed for the frequency compensation of power processors. It has been applied to a converter of the type described by S. Cuk (1986), and it allowed to reach an almost ideal profile of G_loop. The filter copes with converters that chop up to 0.5 MHz and seems to be better than time-invariant compensation networks and DSP-based filters. Exact small-signal analysis of the switching cell and of the compensation filter is carried out, and experimental results of gain and phase frequency dependencies are reported.

[189] J. H. B. Deane and D. C. Hamill, "Instability, subharmonics, and chaos in power electronic systems," IEEE Transactions on Power Electronics, vol. 5, no. 3, pp. 260-268, 1990.

The concept of chaos is applied to a variety of nonlinear power electronic circuits. With the onset of instability, the phenomena of subharmonics, quasi-periodicity, and chaos are predicted and observed. The following examples are dealt with: diodes with charge storage (with application to resonant converters); a ferroresonant circuit; a controlled thyristor rectifier circuit; and a Buck converter controlled by pulse-width modulation (PWM). The examples were chosen to model aspects of real power electronic systems. Analytical and experimental results demonstrate that complex nonlinear phenomena such as subharmonics, quasi-periodicity and chaos can arise in even the simplest systems.

[190] I. Barbi, J. C. O. Bolacell, D. C. Martins, and F. B. Libano, "Buck quasi-resonant converter operating at constant frequency: Analysis, design, and experimentation," IEEE Transactions on Power Electronics, vol. 5, no. 3, pp. 276-283, 1990.

A Buck pulsewidth modulated zero-current switching quasi-resonant converter (Buck PWM ZCS QRC) operating at constant frequency is discussed. Operating principle and design-oriented analysis are presented with normalized design curves, design procedure, design example, simulations, and experimental results. The new topology, which can be considered as a particular one, is compared with the well-established Buck frequency-modulated zero-current switching quasi-resonant converter (Buck FM ZCS QRC) proposed by Fred C. Lee (1988).

[191] R. D. Lorenz and R. A. Cook, "Exact inverter waveform analysis using z-transform estimation techniques," IEEE Transactions on Power Electronics, vol. 5, no. 3, pp. 284-292, 1990.

The critical limitations of Fourier transform analysis are reviewed. The frequency resolution and amplitude accuracy trade-offs implicit in techniques used to minimize the effect of these limitations are presented. The fundamental theory of exact, z-transform modeling that simultaneously offers excellent resolution and accuracy is discussed. The classical techniques used to estimate z-transform coefficients from the sampled data are presented, along with a discussion of their limitations. A new approach for z-transform estimation is developed theoretically, and experimental verification is demonstrated on a PC-AT-based signal acquisition system using actual inverter waveforms.

[192] S. A. Hamed, "Steady-state modeling, analysis, and performance of transistor-controlled ac power conditioning systems," IEEE Transactions on Power Electronics, vol. 5, no. 3, pp. 305-313, 1990.

Steady-state modeling, analysis, and solution of transistor-controlled systems are developed and experimentally verified over a wide range of operation. General features of the system performance and the effects of the chopping frequency on the performance parameters and harmonic generation are thoroughly investigated. Over most of the control range, and for chopping frequencies in the order of several hundred hertz and higher, it is demonstrated that the harmonic contents of the load current are almost negligible, providing highly desired operating conditions for many applications where the fundamental current is the only useful component.

[193] K.-H. Liu and F. C. Y. Lee, "Zero-voltage switching technique in dc/dc converters," IEEE Transactions on Power Electronics, vol. 5, no. 3, pp. 293-304, 1990.

A novel resonant switch operating under the principle of zero-voltage switching is presented. In contrast to the zero-current switching, this technique eliminates the switching loss and dv/dt noise due to the discharging of MOSFET's junction capacitances and the reverse recovery of diodes, and enables the converters to operate at yet high frequencies. The basic configurations of the voltage-mode resonant switches are presented. The circuit's operating principles are described using a voltage-mode quasi-resonant boost converter. DC analysis of the converter is carried out. A new family of voltage-mode quasi-resonant converters are derived, and several members of this family are presented. The dual network theories and the duality principle are briefly reviewed. The duality relationship between the zero-current switching technique and the zero-voltage switching technique is derived. These two techniques are compared using an example showing the duality between a current-mode quasi-resonant Buck converter and a voltage-mode quasi-resonant boost converter. The similarities and differences of the voltage-mode quasi-resonant converters and the Class-E converters are discussed. A 5 MHz 50 V to 5 V flyback converter employing the zero-voltage switching technique has been implemented. The circuit contains the smallest number of components possible, and yet maintains high efficiency at high switching frequency. Design considerations and experimental results of this circuit are presented.

[194] G. Carpenter, F. C. Y. Lee, and D. Y. Chen, "1800-v 300-a nondestructive tester for bipolar power transistors," IEEE Transactions on Power Electronics, vol. 5, no. 3, pp. 314-322, 1990.

A nondestructive reverse-bias safe operating area (RBSOA) tester using an ultra-fast shunt circuit is constructed and demonstrated up to an 1800-V 300-A level. A innovative MOSFET shunt circuit is the key to the high power capability of the tester. The tester is an upgraded version of the old tester (rated at 1000 V 120 A) reported by the authors in 1985. The basic operation of the tester is reviewed, the design and the fabrication of the new tester are described, and test results are provided.

[195] C. K. Tse and K. M. Adams, "Qualitative analysis and control of a dc-to-dc boost converter operating in discontinuous mode," IEEE Transactions on Power Electronics, vol. 5, no. 3, pp. 323-330, 1990.

The boost cell operating in discontinuous conduction mode based on an approximate discrete-time difference equation is investigated. A qualitative discussion of the steady-state and open-loop dynamical behavior is presented. A linearized small-signal equation that leads to a linear feedforward control law for regulating this type of converter is derived. The conventional linear scheme provides satisfactory control in the neighborhood of the operating point, but ceases to meet the requirement as soon as the small-signal assumption is violated. A nonlinear feedforward control law whose validity extends over a wider range of fluctuation of the variables about the operating point is proposed, along with some simulation results that confirm the superiority of the proposed nonlinear control over its linear counterpart.

[196] P. Mehta, M. Darwish, and T. Thomson, "Switched-capacitor filters," IEEE Transactions on Power Electronics, vol. 5, no. 3, pp. 331-336, 1990.

A novel technique for building active filters using switched-capacitor (SC) circuits is proposed. Principle of operation, methods of control, analysis, and design of a typical SC filter is presented. To assess its effectiveness, the technique is used to control input current harmonics in a phase-controlled converter. It is shown that a wide range of harmonics can be controlled using a single filter.

[197] J.-C. Li and Y.-P. Wu, "Closed-form expressions for the frequency-domain model of the series resonant converter," IEEE Transactions on Power Electronics, vol. 5, no. 3, pp. 337-345, 1990.

The steady-state analysis of the series resonant converter is presented using a novel frequency-domain model. Closed-form expressions are derived for the infinite Fourier series. The effects of load resistance, nonzero resistance of the inductor coil, and transistor and diode voltage drops are considered. The output current and voltage characteristics are plotted using the transistor conduction angle as the parameter. The operating point is easily obtained by superimposing on these characteristics a shifted load line that accounts for transistor and diode voltage drops. An example illustrating the solving procedures using the grapical and Newton-Raphison (N-R) methods is included.

[198] Y.-C. Liang and V. J. Gosbell, "Diode forward and reverse recovery model for power electronic spice simulations," IEEE Transactions on Power Electronics, vol. 5, no. 3, pp. 346-356, 1990.

A pn-diode micro-model representing forward and reverse recovery phenomena for power electronic simulation, especially simulations using SPICE2 is presented. The model is proposed to compensate the incompleteness of the diode model in current circuit simulation packages. In the forward recovery submodel, the diode bulk resistance modulation and its forward current dependence are included. In the reverse recovery submodel, the charge control equation for excess storage carriers is employed to simulate the detailed behavior. A procedure is described for extracting the model's physical parameters from data sheet information. The model is verified by a comparison of experimental results for several different tests with SPICE simulations. A discussion is given of extending the applicability of the micro-model to the simulation of p-i-n diode behavior.

[199] P. R. Palmer and C. M. Johnson, "Characterizing the turn-off performance of multi-cathode gto thyristors using thermal imaging," IEEE Transactions on Power Electronics, vol. 5, no. 3, pp. 357-362, 1990.

The thermal imaging of a switching gate-turn-off thyristor (GTO) is described. Using this method, the extent of redistribution occurring at turn-off under various gate drive and anode circuit conditions is determined. The effect of redistribution on the device rating and performance is discussed. Any redistribution in the current will be accompanied by an increase in the losses in the region to turn off last, and a reduction in the losses elsewhere. The experimental procedure for making the switching losses dominant is described. Results show that, under certain gate drive and anode-cathode voltage conditions at turn-off, the anode current redistributes between cathode islands, greatly stressing some islands. From this, conclusions are made concerning GTO rating and circuit design.

[200] A. M. Luciano and A. G. M. Strollo, "Fast time-domain algorithm for the simulation of switching power converters," IEEE Transactions on Power Electronics, vol. 5, no. 3, pp. 363-370, 1990.

An efficient algorithm for the simulation of switched-mode power converters is developed. A Chebyshev series expansion is used to effectively solve the differential equations describing the system in each topology. The power of the new simulation technique lies both in the simple, but accurate, polynomial approximation for the state transition matrices and in the ability to explicitly obtain the instants at which the switching of the circuit topology takes place. The simulation technique is illustrated with reference to a simple Buck converter operating at a constant frequency. The derivation of the new algorithm is presented and its performance is analyzed. The case of a rapidly varying input forcing function is analyzed. Examples illustrating the generality and the computational efficiency of the algorithm are presented.

[201] P. K. Kalra, "Approach for handling the nonlinearities of hvdc system for stability analysis," IEEE Transactions on Power Electronics, vol. 5, no. 3, pp. 371-377, 1990.

An approach for linearizing the nonlinearities of the high voltage direct current (HVDC) system for analyzing the system stability over wide range of operation is presented. The nonlinearities can be linearized with &plusmn5% error over a wide range of system operation. It is shown that the nonlinearities introduced by the converter, real power, and reactive power equations can be linearized over a wide range by using the integral square error (ISE) method. The results are compared with standard techniques called small signal analysis. It is shown that the stability margin of the system predicted by the new technique is relatively smaller than what is predicted by small signal analysis. The system stability boundaries are determined by the AC voltage and the reactive current control. These two control schemes may provide the same stability margin, provided appropriate controller gains are selected. The power factor control modeling is discussed.

[202] T. Kawabata, T. Miyashita, and Y. Yamamoto, "Dead beat control of three phase pwm inverter," IEEE Transactions on Power Electronics, vol. 5, no. 1, pp. 21-28, 1990.

A novel method for microprocessor control of three-phase sinusoidal-voltage pulse-width-modulated (PWM) inverters is proposed. First, the discretized state equations of the inverter main circuit on the d-q frame are derived. An algorithm for deadbeat control with a current minor loop that constrains the inverter current within the safety limit is subsequently developed. To compensate the computing time delay, a second-order prediction method and a novel discretization method using twice the time of the sampling period have been adopted. This method is especially suitable for inverters using high-speed switching devices and digital signal processors. The validity of the control system has been demonstrated by precise simulation using a hybrid computer.

[203] R. B. Ridley, C. Zhou, and F. C. Y. Lee, "Application of nonlinear design optimization for power converter components," IEEE Transactions on Power Electronics, vol. 5, no. 1, pp. 29-40, 1990.

A computer-aided-design approach for power converter components is described. A designer with a minimum of programming and optimization experience can interface with nonlinear optimization routines to perform rapidly design tradeoffs that would be impossible by hand. A power converter design using MOSFET and bipolar-junction-transistor (BJT) switches is shown to illustrate the power of optimization routines in power electronics. Realistic design values and available vendor components can be incorporated in a design without using an extensive database program structure. A practical example is given with experimental data to verify the accuracy and usefulness of optimization software.

[204] V. J. Thottuvelil, T. G. Wilson, and H. A. Owen, Jr., "High-frequency measurement techniques for magnetic cores," IEEE Transactions on Power Electronics, vol. 5, no. 1, pp. 41-53, 1990.

Conventional techniques and new techniques based on digitizing instruments for making high-frequency B-versus-H loop and core-loss measurements on magnetic cores are presented and compared. Potential sources of measurement errors and their magnitudes, limitations imposed by the instrumentation, and thermal considerations are discussed. Circuits suitable for high-frequency sine-wave or square-wave core excitation are also discussed. The utility of such measurements is illustrated with sample data.

[205] J. Lee, D. Y. Chen, and C. Jamerson, "Magamp post regulators - practical design considerations to allow operation under extreme loading conditions," IEEE Transactions on Power Electronics, vol. 5, no. 1, pp. 69-76, 1990.

Practical design equations and guidelines are established to allow magnetic amplifier (magamp) operation under extreme loading conditions. Three conditions are considered: shutdown of output, foldback of the output current, and operation under discontinuous inductor current mode. Design equations are derived for the three extreme operations, and their use is illustrated by numerical examples. The design equations provide the designers with tools for parameter tradeoffs and lend themselves to computer-search design procedures.

[206] S. Fukuda, Y. Iwaji, and H. Hasegawa, "Pwm technique for inverter with sinusoidal output current," IEEE Transactions on Power Electronics, vol. 5, no. 1, pp. 54-61, 1990.

A sinusoidal pulse-width-modulated (PWM) technique suitable for single-chip microprocessor-based control is described. The proposed scheme can be considered as a digital alternative to the conventional subharmonic method in the sense that online real-time PWM control is possible and synchronization between carrier wave and signal wave is unnecessary. The scheme features a maximum output voltage that is 15% greater than for the subharmonic method, and the number of switchings is 30% less. A description of the PWM pulse-creation principle is given. Most inverter loads have a low-pass filter nature. Taking this into account, a performance function (PF), which is the time-integral function of the inverter output voltage, is introduced. An optimal PWM pattern is obtained by minimizing the distortion factor of the PF. As the calculation of the optimal pattern needs only three multiplications, it can be executed online with a minimum read-only-memory capacity using a conventional microprocessor. The experiment was carried out with an Intel 8096 CPU. The results demonstrate the validity of the proposed scheme.

[207] T. Matsui, T. Okuyama, J. Takahashi, T. Sukegawa, and K. Kamiyama, "High accuracy current component detection method for fully digital vector-controlled pwm vsi-fed ac drives," IEEE Transactions on Power Electronics, vol. 5, no. 1, pp. 62-68, 1990.

A high-accuracy, differential-type current component detection method is described, and test results are presented. The method is suitable for vector-controlled pulse-width-modulated (PWM) voltage-source-inverter- (VSI-) fed adjustable-speed AC drives. Its features include elimination of high-frequency current harmonics appearing in PWM VSIs and correction of the detection error caused by the lag time of time-sharing processing. Since this method allows current loop calculations to be made at a slower rate with a conventional microprocessor, it realizes a fully digital speed regulator with a minor current component loop.

[208] J. H. R. Enslin and J. D. Van Wyk, "New control philosophy for power electronic converters as fictitious power compensators," IEEE Transactions on Power Electronics, vol. 5, no. 1, pp. 88-97, 1990.

A new philosophy utilizing both thyristor-controlled reactive sources (TCR) and dynamic power filters (DPF) is proposed for applications in fictitious power compensation. The necessary network parameters for the control loops are calculated from digital time-domain, cross-correlation signal processing techniques implemented with the aid of a microcomputer. Practical results that illustrate this control philosophy were obtained for a 15-kVA three-phase dynamic power filter.

[209] V. Vorperian and R. B. Ridley, "Simple scheme for unity power-factor rectification for high frequency ac buses," IEEE Transactions on Power Electronics, vol. 5, no. 1, pp. 77-87, 1990.

A simple scheme is proposed for offline unity power factor rectification for high-frequency AC buses (20 kHz). A bandpass filter of the series-resonant type, centered at the line frequency, is inserted between the line and the full-wave rectified load. The Q = Z₀/R_L formed by the load and the characteristic impedance of the tank circuit determines the power factor, the boundary between continuous and discontinuous conduction modes, the peak stresses, and the transient response of the rectifier. It is shown that for Q gt; 2/π the rectifier operates in continuous conduction mode and the output voltage is independent of the load. Also, it is shown that for Q gt; 2 the line current is nearly sinusoidal with less than 5% third-harmonic distortion and the power factor is essentially unity. An increase in Q causes an increase in the peak voltages of the tank circuit and a slower transient response of the rectifier circuit. The DC, small-signal, and transient analyses of the rectifier circuit are carried out, and the results are in good agreement with simulation and experimental results.

[210] A. F. Witulski and R. W. Erickson, "Extension of state-space averaging to resonant switches and beyond," IEEE Transactions on Power Electronics, vol. 5, no. 1, pp. 98-109, 1990.

It is shown that the state-space averaging method can be extended by linear network theory from the domain of pulse-width-modulated converters to a much larger class, including resonant switches and current-programmed mode. The canonical model concept is also extended, and it is shown that the effect of resonant switching is to introduce a feedback block into the generalized canonical model. These results are applied to linear zero-current and zero-voltage resonant switches, a new class of nonlinear resonant-switch converters, and the current-programmed mode. Equivalent circuit models are developed for both full- and half-wave operation, and experimental verification is presented.

[211] B. H. Cho, J. R. Lee, and F. C. Y. Lee, "Large-signal stability analysis of spacecraft power processing systems," IEEE Transactions on Power Electronics, vol. 5, no. 1, pp. 110-116, 1990.

The authors present a comprehensive large-signal stability analysis of a solar-array power system. The stability of the equilibrium points of a system with a typical nonlinear load characteristic is analyzed. Employing state-plane analysis techniques, the dynamic behavior of the system from an arbitrary initial condition is characterized, and the region of the desired stable operation is identified. The stability and transient response of the system operation near the solar array's maximum power point are evaluated. The dynamic response of the spacecraft power system operating in the shunt mode and battery-discharge mode is analyzed.

[212] B. Singh, K. B. Naik, and A. K. Goel, "Steady state analysis of an inverter-fed induction motor employing natural commutation," IEEE Transactions on Power Electronics, vol. 5, no. 1, pp. 117-123, 1990.

A steady-state analysis of a three-phase induction motor fed by a DC link inverter commutated by machine-induced emf (electromotive force) is presented. The active power requirement of the motor is met by the DC link, and the necessary reactive power is supplied by a capacitor bank connected at the motor terminals. A generalized analytical model is developed for no-load as well as loaded conditions of the motor. The steady-state performance of the motor is numerically evaluated. The computed results are compared with corresponding experimental results for a 4-hp squirrel cage induction motor. The relevant oscillograms of voltage and current waveforms of the inverter and motor are presented and discussed.

[213] R. E. Shetler and T. A. Stuart, "A 2.5-kw cascaded schwarz converter for 20-khz power distribution," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 381-388, 1990.

The cascaded Schwarz converter, which provides a relatively simple method for driving 20-kHz power systems, is discussed. The cascaded Schwarz is compared with other 20-kHz converters, showing that the circuit is relatively easy to protect and provides a predictable trapezoidal voltage waveform. Because it avoids the high currents in a parallel loaded capacitor, the cascaded Scharwz should offer better component utilization than converters with sinusoidal output voltages. Operation has been verified on a 2.5-kW circuit that uses input and output voltages in the same range as those anticipated for certain future spacecraft power systems.

[214] P. Tenti, L. Rossetto, L. Malesani, R. Borgatti, and R. Stefani, "Single-stage current-fed dc-dc converter with time-sharing control of output voltage and input current," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 389-397, 1990.

A single-stage current-fed DC/DC converter structure and control strategy for simultaneous control of output voltage and current flowing in the input inductor are described. This configuration is suitable for high power-density applications because it results in reduced converter size and power loss. A very fast control-to-output response is obtained, together with stable operation even for large load and reference variations. Static and dynamic converter performances are investigated and design criteria given. Experimental results obtained on a prototype are also reported.

[215] S. Y. R. Hui and C. Christopoulos, "A discrete approach to the modeling of power electronic switching networks," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 398-403, 1990.

An approach to time-domain analysis and modeling of power electronic circuits is described. All circuit components (including active and passive elements) are modeled in a discrete manner by transmission-line sections using the transmission-line modeling (TLM) method. This method requires a fixed system matrix which depends only upon the circuit configuration and time step and not on the switching states of the circuit. Since this method adopts a discrete approach, it provides an exact solution to the discrete model and is stable even for stiff networks. Errors are due to the modeling process only and not to the approximate solution of an approximate calculus model. A simulation on a switched-mode power supply is used to illustrate the modeling method, and the simulated results are compared with measurements.

[216] C. Q. Lee, R. Liu, and S. Sooksatra, "Nonresonant and resonant coupled zero voltage switching converters," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 404-412, 1990.

Two zero-voltage switching converters with nonresonant and resonant coupling are presented. These are high-order multiple resonant converters in which the circuit modes associated with the converter operation may have different resonant frequencies. The steady-state responses of these converters are derived in terms of state-plane diagrams by using proper state variable transformations. It is shown that the converters have all the desirable features for high-frequency applications and overcome the drawback of load-range limitation of zero-voltage switching associated with the conventional class-E converter.

[217] M. Kekura, H. Akiyama, M. Tani, and S.-i. Yamada, "8000-v 1000-a gate turn-off thyristor with low on-state voltage and low switching loss," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 430-435, 1990.

An 8-kV, 1-kA gate turn-off thyristor (GTO) that has been designed with a combination of a p-i-n structure and a ringed-anode short structure is discussed. The GTO has been fabricated using a diffusion and epitaxial buffer process. As a consequence, low on-state voltage and low switching loss have been achieved, solving the two major problems in high-voltage GTOs. The device's structure, the p-i-n base process, and the electrical characteristics of the GTO are described.

[218] T.-H. Liu and C.-H. Liu, "A multiprocessor-based fully digital control architecture for permanent magnet synchronous motor drives," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 413-423, 1990.

The design and implementation of a multiprocessor-based fully digital control architecture for permanent-magnet synchronous motor drives and an approach for designing advanced AC servo drives using currently available high-performance microprocessors are presented. The design of the architecture involves formulation of control algorithms for a current-regulated pulsewidth-modulated inverter and advanced vector-control strategies for speed and position loop. Under the vector-control framework, some recently developed robustness control results are applied to the design of speed-loop controllers. The implementation of the architecture integrates the control of current, speed, and position loop using the multiprocessor-based controller. Experimental case studies that correlate simulation and measurement results are provided. Experiments were conducted to compare the controller performance, including step speed and position responses, closed-loop frequency responses, the effect of field-weakening control, and disturbance-rejection performance. The experimental results validate the theoretical development.

[219] J. H. Spreen, "Electrical terminal representation of conductor loss in transformers," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 424-429, 1990.

The formulation of a general, complete electrical terminal representation of eddy-current loss in transformer windings is presented. It is shown that the effects of mutual resistances must be considered in addition to the familiar winding resistances (self resistances) for a complete description of eddy-current loss. A simple two-foil winding structure is analyzed to display the features of the self- and mutual-resistance terms. The example illustrates that leakage resistance, i.e., resistance associated with opposing winding currents of equal amp turns, provides only a partial description of eddy-current loss. The analysis is extended to multiple windings, with a simple three-foil winding structure as an example.

[220] S. K. Sul and T. A. Lipo, "Field-oriented control of an induction machine in a high frequency link power system," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 436-445, 1990.

A field-oriented controlled induction machine drive operating with a high-frequency single-phase sinusoidal voltage link is presented. System performance is investigated by computer simulation and is verified by test on an actual prototype system. A control loop is proposed for minimizing the link-voltage fluctuation. The capability of rapid demagnetization of the induction machine by current regulation is investigated. A new current modulation technique called switch mode selection is proposed and its performance is compared with the conventional delta modulation technique.

[221] D. S. Zinger, F. Profumo, T. A. Lipo, and D. W. Novotny, "A direct field-oriented controller for induction motor drives using tapped stator windings," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 446-453, 1990.

The implementation of a direct method of field orientation that requires little knowledge of machine parameters and uses only readily measurable quantities is discussed. The system uses tapped stator windings to measure the air-gap flux. The signals from the tapped windings are also used in a flux-regulation loop. A speed controller is implemented using the ripples created in the tapped windings by the motion of the rotor slots through the flux for speed information.

[222] D. A. Philips, "Switched reluctance drives: New aspects," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 454-458, 1990.

A 1-kW switched reluctance drive and an efficient power converter requiring only a low number of switches are introduced. An analytical model of the interactive behavior of the motor and the power converter is developed. The drive is to be essentially torque controlled. The goodness factor of the motor (which expresses how effectively the voltamperes available from the power converter are used for active power conversion) is introduced. In order to increase the goodness factor, premagnetization is applied. The controllability of torque and the premagnetization principle is evaluated by experiments and are found to agree with the theoretical model.

[223] A. R. Hefner, Jr., "An improved understanding for the transient operation of the power insulated gate bipolar transistor (igbt)," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 459-468, 1990.

It is shown that a non-quasi-static analysis must be used to describe the transient current and voltage waveforms of the insulated gate bipolar transistor. The non-quasi-static analysis is necessary because the transport of electrons and holes are coupled for the low-gain, high-level injection conditions, and the quasi-neutral base width changes faster than the base transit speed for typical load circuit conditions. To verify that both of the non-quasi-static effects must be included, the predictions of the quasi-static and non-quasi-static models are compared with measured current- and voltage-switching waveforms. The comparisons are performed for different load circuit conditions and for different device base lifetimes.

[224] D. Naunin, D. Hetzel, H.-C. Reuss, and C. E. Sechelmann, "Completely digital position feedback control for synchronous servodrives," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 495-502, 1990.

A completely digital control concept for a synchronous servodrive is presented. The hardware consists of a pulsewidth-modulated (PWM) inverter and a microcontroller with peripheral components for state-value measurements and set-value output. The derivation of a mathematical model of the PM synchronous servodrive is shown. A cascaded state feedback controller (which consists of a position state feedback controller with an inner-current control loop) is introduced. Two different types of current controllers are compared.

[225] H. Le-Huy, P. Viarouge, and B. Francoeur, "A novel unipolar converter for switched reluctance motor," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 469-475, 1990.

A configuration of a unipolar converter with improved switching performance suitable for switched-reluctance motor supply is presented. The switched-reluctance motor operation principle is presented and its ideal characteristics are considered. The proposed converter is described and its operation is analyzed. The converter characteristics are studied with the aid of computer simulation. Current control of the proposed converter is considered. A prototype converter has been built to verify the analysis results and to validate the simulation. The design procedure is presented and experimental results which confirm the analysis are given and discussed.

[226] I.-J. Lee, D. Y. Chen, Y.-P. Wu, and C. Jamerson, "Modeling of control loop behavior of magamp post regulators," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 476-484, 1990.

Small signal-control models are presented for a magnetic amplifier switching-mode post regulator. Two commonly used current reset schemes are considered; an external reset scheme and a self-reset scheme. It is mathematically shown that the open-loop gain is a two-pole, single-zero transfer function for continuous-mode operation and is a single pole transfer function for discontinuous mode operation. The equations for predicting the open-loop gains for both types of reset circuits are derived and verified experimentally. It is shown that the open-loop gain characteristics of a magnetic-amplifier regulator depends on power-circuit parameters, the reset-circuit parameters, and the saturable reactor parameters. Models for both continuous mode and discontinuous modes of operation that provide designers with useful tools for designing a compensation network for the feedback error amplifier are presented.

[227] G. Joos, P. D. Ziogas, and D. Vincenti, "A model reference adaptive pwm technique," IEEE Transactions on Power Electronics, vol. 5, no. 4, pp. 485-494, 1990.

A model reference adaptive (MRA) pulsewidth-modulated (PWM) technique is presented and analyzed. With this technique, the near optimal inverter gating signals are determined through a closed-loop process which compares a reference signal to a feedback signal derived from a built-in reference model of the load. In addition to its simplicity of implementation, the proposed PWM technique has the adavantages of inherent controlled constant volts-per-Hertz (V/f) ratio operation and jitter-free operation with free-running carrier. Such features are of importance in variable-speed AC-drive applications where V/f control increases the control-circuit complexity and where carrier frequency jumps cause harmful torque/speed transients.

[228] T. Kawabata, N. Sashida, Y. Yamamoto, K. Ogasawara, and Y. Yamasaki, "Parallel processing inverter system," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 442-450, 1991.

A novel method of instantaneous voltage and power balance control of a parallel processing inverter system is proposed. It consists of a high-speed switching PWM (pulsewidth modulated) inverter with an instantaneous current minor loop controller, a voltage major loop controller, and a power balance controller. This system realizes the following functions with only one inverter: 1) Constant AC output voltage control with reactive power control, 2) active filtering to absorb load current harmonics, 3) DC voltage and current control as AC-to-DC converter, and 4) uninterruptible power supply (UPS) for stand-alone operation. This system covers a wide application range, including UPS systems, new energy systems, and active filters with voltage control functions.

[229] J. W. Kolar, H. Ertl, and F. C. Zach, "Analysis of on- and off-line optimized predictive current controllers for pwm converter systems," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 451-462, 1991.

The problem of on-off current control for coupling of a DC voltage system with a three-phase (polyphase) AC voltage system via a pulsewidth modulated (PWM) converter is discussed. The AC voltage represents either the counter EMF (electromotive force) of an AC machine or the three-phase power supply system (mains). The following control concepts are investigated by digital computer simulation: 1) a simple hysteresis controller; 2) a predictive controller with online optimization (optimization with respect to minimum switching frequency); and 3) a controller based on offline optimization (using a switching table). It is shown that the relatively involved predictive controller can be replaced by a switching table of very limited size. For rating of the treated controllers the switching frequency as a function of the RMS voltage of the AC system and the other system parameters is used.

[230] T. G. Habetler and D. Divan, "Angle controlled current regulated rectifiers for ac/ac converters," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 463-469, 1991.

Rectifier control schemes for use in AC/DC/AC voltage-sourced resonant link converters with controlled rectifiers are discussed. It is shown that the voltage-sourced rectifier cannot be operated solely on the basis of instantaneous quantities. A bang-bang control scheme that independently controls the angle and the magnitude of the AC-line current vector is developed and simulated. The magnitude of the current is controlled using a linear combination of the link voltage error and the current magnitude error. The current reference is derived by the use of load torque estimation. In addition, the current vector which satisfies the sliding mode criteria and results in lowest voltage ripple is chosen to further minimize the size of the link capacitor.

[231] S. Ueda, K. Honda, T. Ikimi, M. Hombu, and A. Ueda, "Magnetic noise reduction technique for an ac motor driven by a pwm inverter," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 470-475, 1991.

A technique for reducing magnetic noise from an AC motor driven by a pulsewidth modulation (PWM) inverter is proposed. In this technique, the meaningless magnetic noise is converted into selected information. The technique can be adopted independently of the inverter rated output power. The relationship between carrier waveform frequency in PWM control and harmonics contained in the motor current is first clarified by a harmonics analysis. Then a hardware circuit configuration and carrier frequency control software in a microcomputer are introduced. Using a musical melody as the selected information, the effect of this control is experimentally confirmed. It is shown that the desired sound can be obtained from the AC motor, and the motor voltage and motor current waveforms are not affected by such control.

[232] D. Maksimovic and S. Cuk, "A unified analysis of pwm converters in discontinuous modes," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 476-490, 1991.

Three discontinuous operating modes of PWM (pulsewidth modulated) converters are considered: the discontinuous inductor current mode (DICM), the discontinuous capacitor voltage mode (DCVM), and a previously unidentified mode called the discontinuous quasi-resonant mode (DQRM). DC and small-signal AC analyses are applicable to all basic PWM converter topologies. Any particular topology is taken into account via its DC conversion ratio in the continuous conduction mode. The small-signal model is of the same order as the state-space averaged model for the continuous mode, and it offers improved predictions of the low-frequency dynamics of PWM converters in the discontinuous modes. It is shown that converters in discontinuous modes exhibit lossless damping similar to the effect of the current-mode programming.

[233] R. Dhaouadi, N. Mohan, and L. Norum, "Design and implementation of an extended kalman filter for the state estimation of a permanent magnet synchronous motor," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 491-497, 1991.

Practical considerations for implementing the discrete extended Kalman filter in real time with a digital signal processor are discussed. The system considered is a permanent magnet synchronous motor (PMSM) without a position sensor, and the extended Kalman filter is designed for the online estimation of the speed and rotor position by only using measurements of the motor voltages and currents. The algorithms developed to allow efficient computation of the filter are presented. The computational techniques used to simplify the filter equations and their implementation in fixed-point arithmetic are discussed. Simulation and experimental results are presented to demonstrate the feasibility of this estimation process.

[234] M. Morimoto, K. Sumito, S. Sato, K. Oshitani, M. Ishida, and S. Okuma, "High efficiency, unity power factor vvvf drive system of an induction motor," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 498-503, 1991.

A high-efficiency, unity-power-factor VVVF (variable voltage, variable frequency) drive scheme for an induction motor is presented. A unity-power-factor PWM (pulsewidth modulated) converter regulates DC voltage. An inverter circuit with the magnetic flux control PWM method generates VVVF PWM waveforms. The modulation factor of the inverter PWM control with controllable DC link DC voltage is studied. As a result, the distortion factor and the switching frequency are reduced by over-modulation with low DC link voltage. A high-efficiency and unity-power-factor VVVF induction motor drive has been achieved using the control strategy.

[235] J.-S. Lai and B. K. Bose, "An induction motor drive using an improved high frequency resonant dc link inverter," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 504-513, 1991.

An induction motor drive that uses an improved high-frequency resonant DC link inverter is presented. The resonant circuit was systematically analyzed first to establish the criteria for initial current selection, and a circuit to establish the bidirectional initial current was then proposed. The proposed current initialization scheme solves voltage overshoot and zero crossing failure problems in the ordinary resonant DC link inverters. A three-phase 3-kW insulated-gate-bipolar-transistor (IGBT) based 60 kHz resonant link inverter has been constructed and successfully tested with an induction motor drive. The speed control system is implemented using two microprocessors. Experimental results are presented to show superior operation of the proposed resonant DC link inverter drive.

[236] M.-H. Park and C.-Y. Won, "Time optimal control for induction motor servo system," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 514-524, 1991.

A time-optimal position control scheme based on Pontryagin's minimum principle is proposed for a current-source-inverter (CSI-) fed induction motor system. The induction motor with field-oriented control is modeled with a fast time-optimal position control system of second order which has two modes of operation; the first bang-bang mode operates until the position is close to target, followed by second DC braking mode which gives asymptotic stability. In order to realize this aim, the time-optimal controller is added instead of the speed controller to the conventional field oriented control loop of the CSI-fed induction motor. The validity of the time-optimal control solution has been verified by an experimental test. Experimental results are in a close agreement with a digital simulation.

[237] I. Batarseh and C. Q. Lee, "Steady-state analysis of the parallel resonant converter with llcc-type commutation network," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 525-538, 1991.

A novel converter topology known as LLCC-type parallel resonant converter (PRC-LLCC), in which the tank circuit consists of two inductors and two capacitors, is introduced. Using the state-plane approach, the steady-state analysis of the PRC-LLCC operating in the continuous conduction model is carried out. It is shown that by using the state variable transformation technique the steady-state response of the converter can be represented by two state-plane diagrams. Using these diagrams and the circuit equations, a set of control characteristic curves which are useful for converter design is derived. Based on these curves, a design procedure along with a specific design example is given. The correctness of the analysis results is verified via computer simulations.

[238] K. Shenai, "A circuit simulation model for high-frequency power mosfet's," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 539-547, 1991.

A circuit simulation model suitable for modeling the static and dynamic switching characteristics of high-frequency power MOSFETs is reported. The model parameters were obtained from physical device layout, silicon doping, and measured electrical characteristics of power MOSFETs. Accurate voltage dependencies of the interelectrode capacitances were obtained from extensive two-dimensional device simulations. The voltage dependence of gate-drain capacitance was modeled using an analytic expression. The measured static current-voltage and transient-switching responses under resistive switching conditions are in excellent agreement with simulation results obtained from SPICE. The MOSFET subcircuit model was used to accurately predict the performance of a series-parallel resonant DC-DC converter using a multilevel system simulator.

[239] S. Krauthamer, M. Gangal, and R. Das, "State-of-the art of dc components for secondary power distribution of space station freedom," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 548-561, 1991.

120-V DC secondary power distribution has been selected for Space Station Freedom. State-of-the art components and subsystems are examined in terms of performance, size, and topology. One of the objectives of this work is to inform the users of Space Station Freedom what is available in power supplies and power control devices. The other objective is to stimulate interest in the component industry so that more focused product development can be started. Based on results of this study, it is estimated that, with some redesign, modifications, and space qualification, may of these components may be applied to Space Station Freedom needs.

[240] R. Kelkar, R. A. Wunderlich, and L. J. Hitchcock, "Software breadboards for power electronic circuits," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 170-178, 1991.

A software breadboard is a means of simulating power electronic circuits at the device-level. The objective is to obtain detailed performance information such as device voltage and current waveforms and power dissipations. The intent is to accurately model the circuit for use in place of measurements to assess performance and even in a design mode to pick component values. The issues involved in device level simulation, such as applications, problems, limitations, and advantages, are discussed. An example fullbridge converter is simulated and used for illustration.

[241] V. J. Thottuvelil, D. Chin, and G. C. Verghese, "Hierarchical approaches to modeling high-power-factor ac-dc converters," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 179-187, 1991.

The utility of a hierarchical approach to modeling and simulation in power electronics is illustrated using a high-power-factor (HPF) AC-DC switching converter as an example. The combined use of several modeling techniques and tools is shown to provide comprehensive simulation coverage during analysis and design of the HPF converter. A summary of the various modeling levels, and their application domains and CPU times is given in tabular form. The estimated times are obtained by linear scaling of the measured times for a particular level. The CPU times show the necessity of using a hierarchical approach when simulating extended intervals and/or large circuits.

[242] P. O. Lauritzen and C. L. Ma, "A simple diode model with reverse recovery," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 188-191, 1991.

The basic diode charge-control model used in SPICE is extended to include reverse recovery. The model is derived from the semiconductor charge transport equations. The diode charge transport equations are simplified using the lumped charged concept of Linvill, and the model is demonstrated on the Saber simulator for simple inductive and resistive load circuits. The two model parameters, diode lifetime _τ and diffusion transit time T_M, can easily be determined from a switching waveform.

[243] R. S. Scott, G. A. Franz, and J. L. Johnson, "An accurate model for power dmosfet's including interelectrode capacitances," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 192-198, 1991.

A SPICE-compatible circuit model for power MOSFETs is presented. It is based on device physics and uses a subcircuit representation. The interelectrode capacitances are modeled accurately as nonlinear functions of the applied biases. Various second-order effects relating to the gate capacitance model are discussed, and strategies are presented to include them in the model. The model parameters can be obtained from device measurements. The model is verified by comparing measured and simulated waveforms from a gate charge test circuit.

[244] M. M. Jovanovic, "A transistor model for numerical computation of forward-bias second-breakdown boundary," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 199-207, 1991.

A two-dimensional transistor model for numerical computation of the forward-bias, second-breakdown boundary is proposed. The model takes into account high-current-density effects such as the base-widening (Kirk's) effect and avalanche injection. The numerically determined forward-bias safe operating area is in good agreement with the experimentally obtained area, especially at high collector currents and lower collector voltages. The model is also used to analyze the dynamics of the forward-bias second breakdown. The model is verified experimentally, and is suitable for a parametric study of forward-bias second breakdown.

[245] A. R. Hefner, Jr., "An investigation of the drive circuit requirements for the power insulated gate bipolar transistor (igbt)," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 208-219, 1991.

The drive circuit requirements of the insulated gate bipolar transistor (IGBT) are explained with the aid of an analytical model. It is shown that non-quasi-static effects limit the influence of the drive circuit on the time rate-of-change of anode voltage. Model results are compared with measured turn-on and turn-off waveforms for different drive, load, and feedback circuits, and for different IGBT base lifetimes.

[246] S. Vadivel, G. Bhuvaneswari, and G. S. Rao, "A unified approach to the real-time implementation of microprocessor-based pwm waveforms," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 565-575, 1991.

A method for real-time implementation of any two-level three-phase pulse-width-modulator (PWM) waveform is discussed. The hardware and software of the scheme are built around the 16-b 8086 microprocessor and its peripherals, with a few additional digital ICs. The suggested scheme realizes the PWM waveforms without harmonic distortion. The implementation procedure is a universal one and it generates in real time any two-level three-phase PWM waveform with the chosen hardware structure. There is no need for hardware alteration for realization of different types of PWM waveforms.

[247] K. Thiyagarajah, V. T. Ranganathan, and B. S. R. Iyengar, "A high switching frequency igbt pwm rectifier/inverter system for ac motor drives operating from single phase supply," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 576-584, 1991.

A pulse-width-modulated (PWM) rectifier/inverter system using insulated-gate-bipolar-transistors (IGBTs), capable of switching at 20 kHz is reported. The base drive circuit for the IGBT, incorporating short-circuit protection, is presented. The inverter uses an Undeland snubber together with a simple energy recovery circuit, which ensures reliable and efficient operation even for 20 kHz switching. The front end for the system is a regenerative single phase full-bridge IGBT inverter along with an AC reactor. Steady-state design considerations are explained, and control techniques for unity power factor operation and fast current control of the front end converter, in a rotating as well as a stationary reference frame, are discussed and compared. Results from computer simulations and experimental results for a 1.5-kW prototype system are presented.

[248] Y. Amran, F. Huliehel, and S. Ben-Yaakov, "A unified spice compatible average model of pwm converters," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 585-594, 1991.

A simple, unified, and topology-independent model of basic pulse-width modulated (PWM) converters is developed using the switched inductor approach presented by S. Ben-Yaakov (1989). The model is compatible with SPICE or other similar general-purpose electronic circuit simulators. It can be used to simulate DC, small signal, and transient behavior of PWM converters operating in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM). During simulation, the model automatically follows the CCM and DCM operation, with fewer convergence problems compared to previous simulation models. An effective measurement technique using the HP3562A dynamic signal analyzer (DSA) is presented and applied to compare simulation runs with experimental data. The two were found to be in good agreement.

[249] K. Johansson, K. Lilja, A. Zuckerberger, F. Straker, and H. E. Gruning, "System simulation and realization of a resonant inverter with a field-controlled thyristor," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 220-227, 1991.

The design, simulation, and realization of a single-ended quasi-resonant inverter (SEQRI) for induction heating applications are described. A novel power device, the field-controlled thyristor (FCT), is used as a switching device. Full understanding and a proper realization of the circuit is obtained by accurate simulation with a software tool combining circuit and two-dimensional device simulation. With the use of combined circuit/device simulation the operation of the system is predicted accurately. Comparison with experimental data showed excellent agreement. It is verified that a 15 A/1700 V FCT is an appropriate switching device for a SEQRI fed from a 220 V mains and delivering an output power of 1 kW.

[250] G. L. Skibinski and W. A. Sethares, "Thermal parameter estimation using recursive identification," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 228-239, 1991.

A novel method that converts a semiconductor transient thermal impedance curve (TTIC) into an equivalent thermal RC network model is presented. Thermal resistance (R) and thermal capacitance (C) parameters of the model are identified using manufacturer's data and offline recursive least square (RLS) techniques. Relevant estimation theory concepts and the formulation of an appropriate model for the identification process are given. Model synthesis is illustrated using an isolated base power transistor module. The application of time decoupled theory for high order thermal models is outlined. Simulation of junction temperature responses using model and manufacturer TTICs are compared. Estimated parameter validity is further confirmed by parameter calculation obtained from module physical dimensions.

[251] G. W. Ludwig and S.-A. El-Hamamsy, "Coupled inductance and reluctance models of magnetic components," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 240-250, 1991.

Different models for linear transformers are discussed relative to their use in circuit simulation. These models include: the reluctance model, the permeance model, the inductance matrix model, the T-model, and the reduced T-model. Equations relating the parameter values of the models are derived for the two- and three-winding transformers. A method for direct measurement of the inductance matrix model parameters is described. Guidance is provided for deriving model parameters and using the models in circuit simulators. A model of an ideal transformer using controlled current and voltage sources useful for the T-model is derived. Several examples are discussed.

[252] S. R. Sanders, J. M. Noworolski, X. Z. Liu, and G. C. Verghese, "Generalized averaging method for power conversion circuits," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 251-259, 1991.

A more general averaging procedure that encompasses state-space averaging and that is potentially applicable to a much broader class of circuits and systems is presented. Examples of its application in resonant and PWM converters are presented. The technique is shown to be effective on a number of examples, including resonant type converters. The approach offers refinements to the theory of state-space averaging, permitting a framework for analysis and design when small ripple conditions do not hold. The method may find applications in simulation and design since it is considerably easier to simulate an averaged model than a switched model.

[253] T. Ninomiya, M. Nakahara, T. Higashi, and K. Harada, "A unified analysis of resonant converters," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 260-270, 1991.

The general method of analysis for resonant converters is presented. This analytical method generalizes the idea of state-space-averaging technique to overcome the limitations of the conventional state-space-averaging method. As the result, the characteristics of resonant converters are clarified so that transfer functions and stability conditions are revealed. In addition, a computer program of analysis based on the proposed method is developed. The program can be applied to various resonant converters, even when they have parasitic losses and higher-order resonant circuits.

[254] R. B. Ridley, "A new, continuous-time model for current-mode control," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 271-280, 1991.

A current-mode control model that is accurate at frequencies from DC to half the switching frequency is described for constant-frequency operation. Using a simple pole-zero transfer function, the model is able to predict subharmonic oscillation without the need for discrete-time z-transform models. The accuracy of sampled-data modeling is incorporated into the model by a second-order representation of the sampled-data transfer function which is valid up to half the switching frequency. Predictions of current loop gain, control-to-output, output impedance, and audio susceptibility transfer functions were confirmed with measurements on a buck converter. The audio susceptibility of the buck converter can be nulled with the appropriate value of external ramp. The modeling concentrates on constant-frequency pulse-width modulation (PWM) converters, but the methods can be applied to variable-frequency control and discontinuous conduction mode.

[255] D. Kimhi and S. Ben-Yaakov, "A spice model for current mode pwm converters operating under continuous inductor current conditions," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 281-286, 1991.

A SPICE simulation model of current-mode pulse-width modulation (PWM) converters operating in the continuous mode is described and tested against analytical expressions and experimental data for buck and boost converters. The simulation model is also used to compare an earlier average model to a recently suggested modification and to examine the effect of the gain factor in the current feedback path.

[256] R. Tymerski, "Frequency analysis of time-interval-modulated switched networks," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 287-295, 1991.

A Fourier analysis of time-interval-modulated switched networks is undertaken using time-varying system theory. The result is a linearized describing function approach which determines the small-signal control-to-output (fundamental Fourier component) frequency response. The proposed algorithm is general and exact, and the results are developed in closed form. The intended application area is that of switching DC-to-DC converters where use of the algorithm is demonstrated in deriving an exact analytical expression for the control-to-output transfer function of pulsewidth modulated converters. Experimental results verifying the modeling technique are presented.

[257] S. B. Leeb, J. L. Kirtley, and G. C. Verghese, "Recognition of dynamic patterns in dc-dc switching converters," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 296-302, 1991.

Techniques for analyzing the dynamic patterns of power flow in high-frequency DC-DC switching converters are developed. Emphasis is placed on exploring methods for developing reduced-order instantaneous and averaged models of power electronic circuits for simulation, analysis, and control design. Tools from selective modal analysis are used to develop the dynamic pattern recognition algorithm that facilitates the classification of circuit modules.

[258] J. White and S. B. Leeb, "An envelope-following approach to switching power converter simulation," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 303-307, 1991.

The implementation of an envelope-following method that is particularly efficient for open-loop switching power converters with fixed clock frequencies is described. A simple method for computing envelopes that involves solving a sequence of two-point boundary value problems is derived. The two-point boundary value problems are solved with a shooting or Newton method. The computations involved are explained and their implementation in the Nitswit program, along with results from using it to simulate several switching power circuits, is described. Results demonstrating the method's effectiveness are presented.

[259] S. Singer, "The application of loss-free resistors in power processing circuits," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 595-600, 1991.

Applications of loss-free elements with resistive characteristics in power processing systems are discussed. The synthesis of this kind of element is based on the control of a two port which has a transformer or gyrator matrix. Both of the controlled two ports can be realized by means of switched-mode circuits. The loss-free resistor can be applied to the stabilization of unstable systems, for damping oscillatory waveforms, and balancing of power flow in AC-DC conversion systems. This kind of element has been applied to the stabilization of a gas laser system. It replaced a conventional resistive element which was applied for this purpose.

[260] A. V. Anunciada and M. M. Silva, "A new current mode control process and applications," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 601-610, 1991.

A stability analysis of constant frequency current mode power converters is presented. A current mode control method that overcomes the limited duty of cycle range of stability is introduced. The authors present the application of the control method to half-bridge and full-bridge converters, and describe an improved performance uninterruptilble power supply (UPS) based on the method. The UPS has only one power transformer and one transistor bridge. The authors present detailed experimental results which confirm the advantages of the circuits.

[261] C. T. Rim, G. B. Joung, and G. H. Cho, "Practical switch based state-space modeling of dc-dc converters with all parasitics," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 611-617, 1991.

All parasitics such as switch conduction voltages, conduction resistances, switching times, and ESRs of capacitors are counted in a proposed state-space modeling based method on nonideal switching functions. An equivalent simplified model is derived from the complex circuit with parasitics. The modeling procedure is shown for the buck-boost converter as the general converter among the buck, boost, and buck-boost converters. The pole frequency, DC voltage gain, and efficiency are analyzed and verified by experiments that show good agreement with theory. The procedures for determining the the gain margin of the controller, the turn-ratio of an isolation transformer, the optimum duty factor, and the switching frequency are given for an example fly-back converter.

[262] K. Seki, J.-I. Shida, H. Matsuki, and K. Murakami, "Multi-ability ferrimagnetic semiconductor module for use as a protection and supersonic environmental monitor in the thyristor system," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 630-635, 1991.

The ferrimagnetic semiconductor (FMS) is one type of ferrite belonging to the family of n-type semiconductors with a ferromagnetic property below the Curie temperature. The FMS is a multi-ability device which adds the functions of a magnetostrictive vibrator, a thermistor, a semiconductor capacitor, and a temperature-sensitive magnetic core to a switching element. Techniques for applying the FMS module to protection and supersonic monitor sensors in the thyristor system are discussed.

[263] S. W. Anderson, R. W. Erickson, and R. A. Martin, "An improved automotive power distribution system using nonlinear resonant switch converters," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 48-54, 1991.

An improved automotive electrical system is proposed in which the generator is a high-efficiency AC machine connected to the battery by an AC-DC converter. The electrical loads are isolated from the battery by a DC-DC converter. This will allow gradual conversion to higher battery voltage, regulation of DC distribution voltage, and multiple distribution voltage levels. In the low-voltage, high-current, high-temperature environment of the automobile, in addition to packaging and thermal management, a major problem is the switching loss caused by leakage, package, and other parasitic inductances. The nonlinear resonant switch can remove this source of loss, achieving zero current switching without sacrificing conduction loss or MOSFET switch utilization. For the nonlinear resonant switch in a 1.5-kW load converter application, the upper limit is approximately 20 nH. Hence, device interconnections have low inductance, and MOSFET package inductances are taken into account. A low-voltage, high-current nonlinear resonant switch converter operating at 700 kHz and producing 600 W is described.

[264] C. M. Johnson and P. R. Palmer, "Simulation of wafer-scale gto thyristors in circuits," IEEE Transactions on Power Electronics, vol. 6, no. 2, pp. 308-313, 1991.

A simulation technique that allows the study of large area power devices composed of many outwardly identical elements operating in a realistic power circuit has been developed. Results are presented showing the transient redistribution of current between a pair of GTO thyristor elements during turn-off under the influence of the power circuit. The method is validated by comparing simulated results with experimental measurements. Variations in carrier lifetime, diffusion uniformity, and gate contact position are studied, and they are shown to significantly alter the turn-off performance. Conclusions are drawn concerning the reliability of large area latching power devices with process inhomogeneity.

[265] G. Ledwich, "Current source inverter modulation," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 618-623, 1991.

Pulsewidth modulation strategies are applicable to current source inverters (CSIs). In particular, space vector modulation analysis developed for voltage source inverters (VSIs) is shown to apply to CSI. Using these tools, an equivalence between modulation patterns being used for VSI and those possible for CSI is established. A new modulation pattern is developed and analyzed for an eight-switch CSI, implementing neutral modulation. The analysis tools used to show the CSI/VSI equivalence in the standard case enable analysis of this eight-switch CSI structure. An improved modulation strategy arises from this analysis tool. An experimental eight-switch CSI circuit was constructed and a microcontroller was used to implement modulation based on space vector analysis. The resulting load voltage spectra shows on advantage over standard eight-switch CSIs.

[266] M. Yamamoto and O. Motoyoshi, "Active and reactive power control for doubly-fed wound rotor induction generator," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 624-629, 1991.

A power control system for a doubly fed wound rotor induction generator has been developed. This power control system applies a control method using a rotating reference frame fixed on the gap flux of the generator, and can control active and reactive power independently and stably. The characteristics of the control system have been proved by experiment. Harmonic currents fed to the rotor windings are transmitted to the stator winding changing its frequency. The transmitting characteristics of the harmonic currents have been analyzed and verified by experiments.

[267] S. Y. R. Hui and C. Christopoulos, "Computer simulation of a converter-fed dc drive using the transmission-line modeling technique," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 636-644, 1991.

A modeling technique for the discrete-time domain analysis of power electronics and drive systems is discussed. A discrete model for a converter-fed DC motor drive system has been developed and simulated using this technique. All system components, including the DC machine and power converter, are modeled in a discrete manner as a network of transmission-line sections with the same characteristics as the drive system. The technique isolates the nonlinearity due to the devices' switching action from the system equation and enables a constant system matrix to be used irrespective of the switching state of the power circuit. The algorithm developed provides an exact solution to the discrete model and is easily implemented on desktop computers.

[268] S. M. Williams and R. G. Hoft, "Adaptive frequency domain control of pwm switched power line conditioner," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 665-670, 1991.

An adaptive frequency-domain control algorithm for a pulsewidth modulation (PWM) switched active power line conditioner (PLC) is discussed. An active power line conditioner that minimizes harmonic current in the AC line and improves power factor to unity is recommended. A six switch pulsewidth modulated current source inverter implements the active PLC. Simulation results of the PLC adaptive frequency-domain control using the PWM switching algorithm are presented.

[269] J. Richardson and O. T. Kukrer, "Implementation of a pwm regular sampling strategy for ac drives," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 645-655, 1991.

The regular sampling technique offers a feasible basis for the microprocessor control of inverters in pulsewidth modulated (PWM) AC drives. An implementation of this technique is presented for the speed control of an induction motor in the frequency range 5-105 Hz. Hardware and software design principles are outlined and discussed for an 8-b microprocessor. Spectral analyses of the sampling technique with a sinusoidal modulating function and with a third harmonic added to this function are derived, with emphasis on the fundamental and dominant components. Experimental and computed results are presented for the motor control in steady-state, and for transient current and speed in closed-loop operation, with excellent correlation.

[270] F. D. Rodriguez and J. E. Chen, "A refined nonlinear averaged model for constant frequency current mode controlled pwm converters," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 656-664, 1991.

A refined, duo-mode model for current programmed buck converters is presented. The refined model uses a form of the current mode control law which is truly invariant with respect to operating conditions. That is, it is valid for both transient and steady-state operating conditions regardless of the converter operating mode, which could be etiher continuous conduction mode (CCM) or discontinuous conduction mode (DCM). The large-signal transient response predicted using the refined average model is shown to be virtually indistinguishable, in an average sense, from that predicted using a pulse-by-pulse simulation. The refined model is shown to exhibit improved high-frequency accuracy in both time and frequency domains. The model has been implemented in SPICE 2G6 and runs with default analysis options.

[271] O. D. Patterson and D. M. Divan, "Pseudo-resonant full bridge dc/dc converter," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 671-678, 1991.

A DC-DC converter topology that combines the ease of control and wide range of conventional DC-DC converters, with low switching losses, low dv/dt and low electromagnetic interference that is typical of zero voltage switched resonant converters is proposed. Consequently, the ratings of these components are substantially lower than for similarly rated resonant topologies. While resonant elements are used to ensure zero voltage switching of all devices, they have little or no role in the actual power transfer and can thus be reasonably sized. As the resonant elements are not involved in the primary power transfer, the converter is referred to as a pseudo-resonant converter. It is shown that the converter offers significantly higher levels of performance than either the pulsewidth-modulated (PWM) or typical resonant converters. Operation at very high frequencies is possible and is shown with the fabrication of a 200-W 1-MHz DC-DC converter.

[272] V. A. Sankaran, J. L. Hudgins, C. A. Rhodes, and W. M. Portnoy, "A numerical approach based on transient thermal analysis to estimate the safe operating frequencies of thyristors," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 679-686, 1991.

The spatio-temporal distribution of temperatures in high-power SCRs used for switching high di/dt current pulses were simulated using the finite element method (FEM). Two types of SCRs, with amplifying gate (unshorted device), and without amplifying gate (shorted device) structures, were analyzed. The details of the numerical simulation, such as the meshing strategy, the heat source model, and the boundary conditions are discussed. Based on the analysis, the failure temperature of the unshorted device was computed to be 1100°C. The peak temperature in the shorted device was, however, found to be 335°C. The instantaneous cooling cycles of the devices and their cooling time constants, as obtained from the simulations, are presented. Based on these parameters, the safe operating frequencies of these devices were estimated.

[273] J. He and N. Mohan, "Parallel resonant dc link circuit--a novel zero switching loss topology with minimum voltage stresses," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 687-694, 1991.

A parallel-resonant DC link (PRDCL) circuit topology is proposed as an approach to realizing zero-switching-loss DC-AC high-switching-frequency power conversion. The proposed circuit is used as an interface between the DC voltage supply and a voltage source pulsewidth modulated (PWM) inverter to provide a short zero voltage period in the DC link of the inverter to allow zero voltage switchings to take place in the PWM inverter. The peak voltage stress on the PWM inverter switches is limited to the DC supply voltage. Another significant advantage of the circuit is that the inverter can be controlled by the conventional PWM strategy. The proposed circuit is systematically analyzed and its operation principle is explained. Design considerations and design formulas are presented. A complete zero voltage switching DC-DC system consisting of the proposed circuit and a PWM inverter was simulated on a computer.

[274] R. Krishnan and A. S. Bharadwaj, "A review of parameter sensitivity and adaptation in indirect vector controlled induction motor drive systems," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 695-703, 1991.

The effects of parameter sensitivity on indirect vector control induction motor drives are reviewed. The importance of parameter adaptation is discussed and categorized based on the extent of use of the induction motor parameters. The parameter sensitivity and compensation study is important form the point of view of optimum motor and converter use. The scope for future research and some of the subsets of parameter compensation research are identified, and a detailed survey of the literature available in this topic is given.

[275] D. M. Sable, B. H. Cho, and R. B. Ridley, "Use of leading-edge modulation to transform boost and flyback converters into minimum-phase-zero systems," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 704-711, 1991.

In leading-edge modulation, the pulsewidth-modulated (PWM) signal is turned off at the clock signal and turned on when the error signal crosses the ramp waveform. It is shown that the positive zero in the power stage transfer function of boost and flyback regulators can be shifted into the left-half-plane under suitable conditions. These conditions are as follows: 1) leading-edge modulation must be used in the pulsewidth-modulator, 2) the feedback compensation must not average the capacitor EST-generated output voltage switching ripple, and 3) appropriate power stage parameter values are necessary. The design procedure for shifting the positive zero into the left-half-plane is presented. Experimental verification is provided.

[276] R. Tymerski, "Volterra series modeling of power conversion systems," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 712-718, 1991.

The nonlinear control-to-output response of pulsewidth modulated (PWM) conversion systems is modeled via the Volterra functional series. A brief overview of the series is presented. It is seen that the Volterra series is a power series with memory. Each term in the series represents a convolution integral. The nonlinear response of the system, for any input, can thus be determined from a knowledge of the multidimensional Volterra kernels or impulse responses. The determination of the Volterra kernels in the transform domain is performed on a simplified state-space model of the converter. The dominant component of various harmonic and and intermodulation distortion frequency products in the output spectrum is derived and is expressed in terms of these kernels. Experimental results are presented confirming the modeling procedure.

[277] A. K. S. Bhat and F. D. Tan, "A unified approach to characterization of pwm and quasi-pwm switching converters: Topological constraints, classification, and synthesis," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 719-726, 1991.

Topological constraints are obtained for pulsewidth-modulation (PWM) (under both continuous and discontinuous current modes) and quasi-PWM (including families of quasi-resonant and quasi-square-wave) converters by identifying their three structures. Switching sequences of these converters and a classification of quasi-PWM converters are presented. A dual circuit of an ideal diode and an ideal switch are proposed and used to obtain duals of the switching converters in one step. A procedure for the synthesis of quasi-PWM converters is presented.

[278] A. K. S. Bhat, "A resonant converter suitable for 650-v dc bus operation," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 739-748, 1991.

A high-frequency resonant converter configuration suitable for operation on a 650-V (nominal value) DC bus is described. Selection of the high-frequency switch and an appropriate resonant configuration are discussed. It is shown that a series-parallel resonant converter using insulated gate bipolar transistor (IGBT) gated bipolar/MOSFET cascode switches and operating above resonance is suitable for this application. A simplified analysis, a simple design procedure, and detailed experimental results are presented.

[279] A. R. Prasad, P. D. Ziogas, and S. Manias, "An active power factor correction technique for three-phase diode rectifiers," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 83-92, 1991.

A novel active power factor correction method for power supplies with three-phase front-end diode rectifiers is proposed and analyzed. The implementation of this method requires the use of an additional single switch boost chopper. The combined front-end converter draws sinusoidal AC currents from the AC source with nearly unity input power factor while operating at a fixed switching frequency. It is shown that when the active input power factor correction stage is also used to requlate the converter DC bus voltage, the converter performance can improve substantially in comparison with the conventional three-phase AC-to-DC converters. These improvements include component count reduction, simplified input synchronization logic requirements, and smaller filter refractive components. Theoretical results are verified experimentally. The proposed method has the disadvantage of substantially increasing the current stresses of the switching devices and the high-frequency ripple content of the prefiltered AC input currents.

[280] F. Huliehel and S. Ben-Yaakov, "Low-frequency sampled-data models of switched mode dc-dc converters," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 55-61, 1991.

A sampled data model of a switched mode converter applicable for the low-frequency range is presented. The assumption made is that the sampling rate is sufficiently high, as dictated by the sampling theorem. It is shown that the models are linear for small signal operation but represent a bilinear discrete system under large signal conditions. The models could be useful for the design of microprocessor-based controllers for switched mode converters, with improved transient response. Two examples of possible applications of the model are discussed: as a fast and efficient time-domain simulator and as a tool for the analysis and design of a fast turn-on boost converter. Experimental measurements and computer simulation of the responses to large steps of the duty ratio in a boost converter demonstrate the accuracy of the model at the tested low-frequency region. The bilinear model can be used as a simulation tool for fast and efficient computer-aided analysis and design. The main limitation of the model is its restriction to the low-frequency range. This limitation is alleviated by the present trend in technology toward higher switching frequencies. The applicability of the model for solving practical design problems is illustrated by considering the problem of output capacitor charging rate in a boost converter. It is shown that a considerable improvement in charging rate can be achieved by using a simple duty ratio control law. Other possible areas of application of the model include analysis and design of digital control strategies for microprocessor-based DC-AC inverters and fast-response programmable DC-DC converters.

[281] J. H. R. Enslin and D. B. Snyman, "Combined low-cost, high-efficient inverter, peak power tracker and regulator for pv applications," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 73-82, 1991.

A novel compound power converter that serves as a DC-to-AC inverter, maximum power point tracker (MPPT), and battery charger for stand-alone photovoltaic (PV) power systems is introduced. A theoretical analysis of the proposed converter is performed, and the results are compared with experimental results obtained from a 1.5-kW prototype. The overall cost of PV systems can thus be reduced by using load management control and efficiency-optimization techniques. Power flow through the converter is controlled by means of a combination of duty cycle and output frequency control. With load management, large domestic loads, such as single phase induction motors for water pumping, hold-over refrigerators, and freezers, can be driven by day at a much higher energy efficiency. This is due to the high efficiency of the inverter with high insolation, and because the inverter uses the energy directly from the solar array. The battery loss component is thus reduced. The PV array voltage and the battery voltage can be independently optimized to ensure the lowest possible PV system cost. Only two switching elements are used in the compound converter. With the aid of load management the energy demand at nighttime can be much lower than the day, and therefore the battery capacity (and thus the cost) can be reduced significantly. A lower nighttime demand prevents deep discharge of the batteries, and thus extends battery life. Higher PV system efficiency, and thus lower overall costs, can be obtained due to parallel operation of the converter as an MPPT, battery regulator, and inverter.

[282] A. Mertens and H.-C. Skudelny, "Switching losses in a gto inverter for induction heating," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 93-99, 1991.

The application of gate-turn-off thyristors (GTOs) to parallel resonant inverters for induction heating is investigated. Three different modes of operation of the GTOs are explained and tested in a test circuit. The optimum mode is selected by switching loss measurement. It is shown that due to the small inductance in the commutation circuit, the gate-assisted turn-off technique leads to very high turn-on losses and is not the optimum way to drive the GTO in this application. However, it can be used under different conditions in order to reduce turn-off losses. It is suggested that a mixed turn-off of the devices by both gate action and natural communication is the optimum mode of operation. Then, the load is driven at unity power factor. In this mode of operation, no snubbers are necessary in principle. A small capacitor in parallel to the GTO is recommended for only the staring procedure. An estimation of the total power loss in the GTOs leads to the result that the GTO tested can be operated at frequencies between 10 kHz and 20 kHz with a reasonable inverter efficiency.

[283] G. Roy and G.-E. April, "Direct frequency changer operation under a new scalar control algorithm," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 100-107, 1991.

A thorough analysis of a scalar control method for the operation of direct frequency changers (DFC) using bidirectional switches operating at high switching frequencies is proposed. The method allows full control over voltage and frequency at the output port and the input side power displacement factor, with little effect on the frequency spectrum of either the output voltage or input currents. The method uses the instantaneous voltage ratio of specific input phase voltages to generate the active and zero states of the various switches. A voltage transfer ratio as high as 0.87 is obtained under synchronous and asynchronous operation with a conventionally connected three-phase load. Analysis shows that the input power displacement factor is independent of load characteristics. The power displacement can be precisely controlled by proper adjustments of the timing sequence. Synchronization error in the timing sequence affects both the input power displacement and the voltage transfer ratio.

[284] S. Sangwongwanich, M. Ishida, S. Okuma, Y. Uchikawa, and K. Iwata, "Time-optimal single-step velocity response control scheme for field-oriented induction machines considering saturation level," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 108-117, 1991.

A time-optimal single-step velocity response control scheme of field-oriented induction machines, taking magnetic saturation of rotor flux into account, is implemented based on the analytical solutions of the time-optimal control problem. High velocity response is achieved in spite of field-weakening for low acoustic noise or high-efficiency drives. The equation of the optimal control law is derived, and the look-up table is obtained. The optimal control scheme is realized by simply adding the look-up table to the flux controller of the variable flux field-oriented control system. Simulation is carried out to verify feasibility of the proposed control algorithm. Problems of the overshoot of the rotor speed and the constraint on rate of change of acceleration or deceleration at the instant of switching from the time-optimal control to the conventional field-oriented control are discussed. The experimental results agree well with the simulation results, and show satisfactory dynamic and steady-state performance on both startup and acceleration/deceleration. The merits of the time-optimal control scheme are discussed in comparison with other control schemes. It is concluded that in the case that the saturation level is low compared with the allowable maximum input current, the control of the field current during transient becomes more significant.

[285] D. Maksimovic and S. Cuk, "A general approach to synthesis and analysis of quasi-resonant converters," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 127-140, 1991.

A method for systematic synthesis of quasi-resonant (QR) topologies by addition of resonant elements to a parent pulse-width modulation (PWM) converter network is proposed. It is found that there are six QR classes with two resonant elements, including two novel classes. More complex QR converters can be generated by a recursive application of the synthesis method. Topological definitions of all known and novel QR classes follow directly from the synthesis method and topological properties of PWM parents. The synthesis of QR converters is augmented by a study of possible switch realizations and operating modes. In particular, it is demonstrated that a controllable rectifier can be used to accomplish the constant-frequency control in all QR classes. Links between the QR converters and the underlying PWM networks are extended to general DC and small-signal AC models in which the model of the PWM parent is explicitly exposed. Results of steady-state analyses of selected QR classes and operating modes include boundaries of operating regions, DC characteristics, a comparison of switching transitions and switch stresses, and a discussion of relevant design trade-offs.

[286] D. Maksimovic and S. Cuk, "Constant-frequency control of quasi-resonant converters," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 141-150, 1991.

An additional independent control needed to eliminate the undesirable variable switching frequency of quasi-resonant (QR) converters is obtained by replacing the output rectifier by an active switch. The concept is applicable to all classes of converters. Compared to QR converters with conventional switch realization, constant-frequency quasi-resonant (CF-QR) converters exhibit the same type of switching transitions and similar switch voltage and current stresses. Advantages of CF-QR converters are not restricted to the constant-frequency control. In all classes, operation at zero load is possible, so that the available load range is unlimited. The range of attainable conversion ratios is significantly extended in the classes of zero-voltage quasi-square-wave (CF-ZV-QSW) and zero-voltage multiresonant (CF-ZV-MR) topologies. A practical design example of a 25-W CF-ZV-MR buck converter is constructed and evaluated. The converter operates at 2 MHz from zero load to full load, with a full-load efficiency of 83%. Simple duty ratio control is used to maintain the output voltage constant for all loads. The circuit is inherently immune to the short-circuit condition at the output. Disadvantages of CF-QR converters are the increased gate-drive losses and increased complexity of the power stage and the control circuitry.

[287] M.-H. Park and K.-S. Kim, "Chattering reduction in the position control of induction motor using the sliding mode," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 317-325, 1991.

An induction motor position control system based on the sliding mode control is presented. In the sliding mode control, the control function is discontinuous on the hyperplane, which causes harmful effects such as current harmonics and acoustic noise in the motor drive application. A low-pass filter is introduced between the sliding mode controller output and the motor controller input to reduce these effects. Although the filter smooths the motor input current and alleviates the vibration at the final reference position, it may cause sluggish response in transient condition. To overcome the problem, a variable-bandwidth filter is proposed. In steady state, the bandwidth of the filter is made to be narrow to mitigate the ripple components while it is widened during the transient to improve the response. To achieve such an operation, the bandwidth of the filter is adjusted according to the error function. The proposed method shows good performance, which is confirmed through computer simulation and experiments.

[288] H. W. Klesser and J. B. Klaassens, "Transformer-induced low-frequency oscillations in the series-resonant converter," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 326-337, 1991.

The authors demonstrate the existence of a number of modes of transformer-induced low-frequency oscillations (TLOs) which can be observed in the series-resonant power converter with a transformer in the resonant circuit, operating under conditions of cyclic stability. The TLO phenomena are mathematically analyzed and the conditions of existence are determined. Experimental observations confirm the outcomes of the mathematical analyses. The critical aspects of the TLO phenomena with respect to the converter performance are explored.

[289] D. Maksimovic and S. Cuk, "Switching converters with wide dc conversion range," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 151-157, 1991.

Compared to basic converter topologies (buck, boost, buck-boost, Cuk, etc.), pulse-width modulation (PWM) converters with quadratic DC conversion ratios, M(D) = D², M(D) = D²/(1 - D) or M(D) = D²/(1 - D)², offer a significantly wider conversion range. For a given minimum ON-time and, consequently, for a given minimum duty ratio D_min, D² in the numerator of M(D) yields a much lower limit on the minimum attainable conversion ratio. By applying a systematic synthesis procedure, six novel single-transistor converter configurations with quadratic DC conversion ratios are found. The simpler, single-transistor realization is the most important advantage over the straightforward cascade of two basic converters. As far as conversion efficiency is concerned, it is clear that a single-stage converter is usually a better choice than a two-stage converter. The quadratic converters proposed are intended for applications where conventional single-stage converters are inadequate--for high-frequency applications where the specified range of input voltages and the specified range of output voltages call for an extremely large range of conversion ratios. Following a discussion of basic properties of the quadratic converters in the continuous and the discontinuous modes, two illustrative experimental examples are presented. They include a 20-W, 5-V-output converter supplied from a highly unregulated line voltage (10 V < V_g < 100 V), and a 60-W, 1-60-V-output converter for a laboratory power supply. Although in both cases a step-down of more than 20 to 1 is required, the quadratic converters can operate at a relatively high switching frequency (500 kHz) because the minimum ON-time limitation is much less restrictive.

[290] M. P. Kazmierkowski, M. A. Dzieniakowski, and W. Sulkowski, "Novel space vector based current controllers for pwm-inverters," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 158-166, 1991.

Two novel, simple control strategies for current-controlled pulse-width modulated (PWM) transistor inverters are presented. Both methods are based on the three-level hysteresis comparators which select appropriate inverter output voltage vectors via a switching electrically programmable read-only memory (EPROM) table. The first controller works with current components represented in a stationary coordinate system (AC components) and the second with components represented in a rotated (field-oriented) coordinate system (DC components). The theoretical principles of these methods are discussed. The results of a comparative study, which illustrates the performance of the proposed controller in comparison to the most popular scheme (based on three independent two-level hysteresis comparators), are presented.

[291] M.-G. Kim and M.-J. Youn, "An energy feedback control of series resonant converter," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 338-345, 1991.

An energy feedback control utilizing the resonant tank circiut energy as an inner feedback loop is proposed to improve the stability and dynamic characteristics of the series resonant converter (SRC). The energy-feedback-controlled SRC is modeled and analyzed in discrete time domain. In this analysis, the eigenvalues of the controlled system are dependent on the energy feedback gain ratio, and the design guidelines which can be used to select this ratio are derived. Experimental results show a good agreement with theoretical analysis.

[292] J. B. Klaassens and F. de Beer, "Three-phase ac-to-ac series-resonant power converter with a reduced number of thyristors," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 346-355, 1991.

Power pulse modulation with internal frequencies of tens of kHz and suited for multikilowatt power levels is applied to a series-resonant converter (SRC) system for generating synthesized multiphase bipolar waveforms with reversible power flow and low distortion. The high pulse frequency allows the application of the principle of modulation and demodulation for fast system response. The use of an SRC for power transfer and control obtains natural current commutation of the thyristors and the prevention of excessive stresses on components. Switches with bidirectional current conduction and voltage blocking ability are required. The conventional series-resonant AC-AC converter applies a total for 24 antiparallel thyristors. An alternative circuit configuration for the series-resonant AC-AC converter with only 12 thyristors is presented. Use of the converter results in a higher efficiency and lower costs.

[293] T. G. Habetler and D. M. Divan, "Acoustic noise reduction in sinusoidal pwm drives using a randomly modulated carrier," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 356-363, 1991.

Acoustic noise in an inverter-driven electric machine can be reduced by avoiding the concentration of harmonic energy in distinct tones. One method to spread out the harmonic spectrum without the use of programmed PWM (pulse width modulation) is to make the switching pattern random. It is proposed that the switching pattern can be randomized by modulating the triangle carrier in sinusoidal PWM with bandlimited white noise. All of the advantages of sinusoidal PWM are preserved with this technique. These include, real-time control, linear operation, good transient response, and a constant average switching frequency. By controlling the bandwidth and RMS value of the bandwidth limited noise modulation, it is shown that the instantaneous variation in switching frequency and the bandwidth of the energy spectrum in the machine can be specified within predetermined limits. Experimental results show the absence of acoustic noise concentrated at specific tones, which is present in conventional sinusoidal modulation.

[294] E. Wernekinck, A. Kawamura, and R. Hoft, "A high frequency ac/dc converter with unity power factor and minimum harmonic distortion," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 364-370, 1991.

A novel forced commutated AC/DC converter and control strategy is proposed that is able to draw nearly sinusoidal currents at unity power factor from three-phase power lines. The power factor is controlled by adjusting the relative position of the fundamental component of an optimized pulse-width-modulation (PWM) type voltage with respect to the supply voltage. Current harmonic distortion is minimized by the use of optimized firing angles for the converter at a frequency where gate turn-off thyristors (GTOs) can be used. This feature makes this approach attractive at power levels of 100 kW to 600 kW. An 8096 microcontroller is used to minimize the interface hardware requirements. The theoretical analysis of the converter, the control energy, and experimental results for a low-power prototype are presented.

[295] P. Viriya and K. Matsuse, "Low-harmonic gto converter for fundamental power factor compensation," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 371-379, 1991.

A low-harmonic GTO (gate turn-off) thyristor AC-to-DC converter with line current lead-lag phase shift control ability is proposed and analyzed. The converter can be used either as a low-harmonic GTO-controlled rectifier or a fundamental input power factor compensator in a power supply system. The effect of PWM (pulse width modulation) current phase number on the harmonic contents and converter output voltage control range is investigated. Lower order input current harmonics are eliminated over a wide range, using a specially designed PWM current pattern. The effect of the PWM current pulse number on the power factor compensation characteristic is investigated.

[296] G. Joos, L. Moran, and P. Ziogas, "Performance analysis of a pwm inverter var compensator," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 380-391, 1991.

The performance of a three-phase solid-state reactive power compensator with fast dynamic response is analyzed. The compensator consists of a three-phase pulse-width modulated voltage-source inverter connected to a self-controlled DC bus. The principal advantage of this scheme is that it can maintain a near-unity source power factor without sensing and computation of the associated reactive power component. A mathematical model for the compensator connected across a variable power factor load is derived. The frequency response is obtained for open-loop operation. This allows the design of the controller. Predicted results are verified experimentally for both open- and closed-loop responses.

[297] L. Malesani, L. Rossetto, and P. Tenti, "Active power filter with hybrid energy storage," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 392-397, 1991.

An active power filter that uses an impressed current converter and an inductive-capacitive energy storage circuit is presented. This storage includes a switching section to interface the inductive and capacitive element. This solution allows independent choice of the converter configuration and of the type of storage system which, in this particular case, is mainly capacitive. The theory of operation is analyzed, together with control strategy and design criteria. Experimental results are reported.

[298] A. F. Witulski, "Buck converter small-signal models and dynamics: Comparison of quasi-resonant and pulsewidth modulated switches," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 727-738, 1991.

The generalized canonical model obtained from extended state-space averaging is used as a design tool for the evaluation of the buck converter dynamics in different switching schemes. Designs are given at a specified constant conversion ratio and load for the pulsewidth modulated, zero current, zero voltage, and nonlinear resonant switch full- and half-wave converters. The small signal equivalent circuit model is discussed, and the feedback effects introduced by resonant switching on line and control transfer functions are evaluated. The small signal transfer functions of half-wave converters are heavily load-current dependent, and exhibit significant damping at light loads, which can result in two real poles in the converter response instead of a complex conjugate pair. This damping effect is evaluated over the entire normalized load current range for the linear and nonlinear zero-current switching converters. Simple approximate expressions are given for the real poles. Experimental verification of the half-wave analysis is presented, and the effects of converter efficiency on model accuracy are discussed.

[299] L. F. Casey, J. Ofori-Tenkorang, and M. F. Schlect, "Cmos drive and control circuitry for 1-10 mhz power conversion," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 749-758, 1991.

The design, implementation, and experimental evaluation of CMOS subcircuits that can be combined to implement integrated control and drive for 1-10 MHz power circuits are presented. The approach taken is to develop controller/driver ICs for a specific prototype converter. By maximizing the performance of the different subcircuits in successive design iterations, the fundamental questions about the viability of CMOS technology for high-frequency controller/driver applications can be answered. The ability of CMOS to satisfactorily perform at these high frequencies is documented.

[300] M. J. Gorman and M. E. Elbuluk, "A simple two-switch cycloconverter for variable-frequency low-speed applications," IEEE Transactions on Power Electronics, vol. 6, no. 4, pp. 759-764, 1991.

A two-switch cycloconverter circuit that converts single-phase alternating current into an effective three-phase alternating current is presented. Since this design features only two bidirectional switches, it has a simple and inexpensive construction. The design requires a control circuit, which assures that the average output voltage on its two switches is sinusoidal with a 60°-difference in phase. The results of some simulation studies and an experimental model of the two-switch cycloconverter are discussed. Some problems and potential areas of circuit improvement are presented.

[301] B. A. Miwa, L. F. Casey, and M. F. Schlecht, "Copper-based hybrid fabrication of a 50-w, 5-mhz 40-v-5-v dc/dc converter," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 2-10, 1991.

A prototype 50-W, 40-V to 5-V DC/DC converter operating at 5 MHz and constructed with chip and wire hybrid techniques on a ceramic substrate with copper thick-film conductors is presented. A brief discussion of the thick-film process is given to point out the special issues concerning copper-based conductor systems. Some of the specific tradeoffs that arise with regard to the construction of a power circuit with hybrid techniques are discussed. A method by which transformers may be fabricated to have very little leakage inductance, both internally and in their connection to rectifiers, is then described. The performance of a power circuit, the dual resonant forward converter, is presented.

[302] J. A. Sabate and F. C. Y. Lee, "Off-line application of the fixed-frequency clamped-mode series resonant converter," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 39-47, 1991.

The performance of the clamped-mode series resonant converters (CMSRC) is studied for an offline application. The CMSRC has the advantage of fixed-frequency operation, resulting in an easier design of magnetic components for resonant tank and filtering. Two prototypes were designed and tested experimentally, one to operate below resonant frequency (mode B) and the other to operate above resonant frequency (mode A). The efficiency is mainly determined by the rectifier losses and the switching losses. Where mode-B operation is implemented (below resonant frequency), the recovery of the diodes greatly increases the turn-on losses of the devices. The operation mode with four switches turned on at zero voltage, mode A' at above resonant frequency, shows better efficiency. Therefore, if higher frequencies of operation are desired, mode A' is the better choice among the four modes of operation discussed.

[303] T. M. Jahns, R. C. Becerra, and M. Ehsani, "Integrated current regulation for a brushless ecm drive," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 118-126, 1991.

An enhanced means of regulating phase currents in a brushless electronically commutated motor (ECM), without the use of any discrete current sensors such as shunts or current transformers, is described. Current feedback information is provided by current sensors integrated into MOS-gated power switches (MOSFETs and IGBTs), and the current regulation is performed by gate drive power integrated circuits. A high degree of drive circuit integration is achieved with this scheme, in addition to providing protection against dangerous fault currents not sensed by conventional bus-shunt configurations. Available power semiconductor switches and power integrated circuits make this technique applicable to permanent magnet ECM drives operating at bus supply voltages up to 500 VDC with power ratings from fractional to gt;10 hp.

[304] A. F. Witulski, A. F. Hernandez, and R. W. Erickson, "Small signal equivalent circuit modeling of resonant converters," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 11-27, 1991.

A general analytical procedure is presented for the equivalent circuit modeling of resonant converters, using the series and parallel resonant converters as examples. The switched tank elements of a resonant converter are modeled by a lumped parameter equivalent circuit. The tank element circuit model consists, in general, of discrete energy states, but may be approximated by a low-frequency continuous time model. These equivalent circuit models completely characterize the terminal behavior of the converters and are solvable for any transfer function or impedance of interest. With the approximate model it is possible to predict the lumped parameter poles and zeros, and to quickly determine the relevant DC gains of the output impedance and the control to output transfer function. Closed-form solutions are given for the equivalent circuit models of both converter examples. Experimental verification is presented for the control-to-output transfer functions of both series and parallel resonant converters, and good agreement between theoretical prediction and experimental measurement is obtained. Experimental measurement of the output impedance confirms the observation that, since the filter elements dominate the high-frequency response to disturbances on the converter output, it is sufficient to use the DC value of the tank self-impedance R₂₂ to theoretically predict the output impedance.

[305] R. B. Ridley, W. A. Tabisz, F. C. Y. Lee, and V. Vorperian, "Multi-loop control for quasi-resonant converters," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 28-38, 1991.

A multiloop control scheme for quasi-resonant converters (QRCs) is described. Like current-mode control for pulse width modulation (PWM) converters, this control offers excellent transient response and replaces the voltage-controlled oscillator (VCO) with a simple comparator. In this method, referred to as current-sense frequency modulation (CSFM), a signal proportional to the output-inductor current is compared with an error voltage signal to modulate the switching frequency. The control can be applied to either zero-voltage-switched (ZVS) or zero-current-switched (ZCS) QRCs. Computer simulation is used to demonstrate the effectiveness of the control method applied to a ZCS buck QRC. A circuit implementation is presented that allows multiloop control to be used on circuits switching up to 10 MHz. This circuit requires few components and produces clean control waveforms. Experimental results are presented for zero-current flyback and zero-voltage buck QRCs, operating at up to 7 MHz. Good small-signal characteristics have been obtained. The crossover frequency of the loop gain is limited only by the choice of operational amplifier. With this control scheme, it is possible to push the loop-gain crossover frequency beyond 1 MHz for a 5-10 MHz converter. This increase in crossover can significantly affect the size of the power-stage components, especially the output filter capacitor.

[306] T. Kawabata, T. Miyashita, and Y. Yamamoto, "Digital control of three-phase pwm inverter with lc filter," IEEE Transactions on Power Electronics, vol. 6, no. 1, pp. 62-72, 1991.

A digital control algorithm for the three-phase sinusoidal voltage inverter with an output LC filter has been developed. To take the transient of the LC filter during the discretization time into consideration, a fourth-order matrix state equation of the current and the voltage on the d-q frame is discretized. Precise discrete equations for the inverter are introduced. Using these equations, a deadbeat controller consisting of a d-q current minor loop and a d-q voltage major loop, with precise decoupling of the d-q components, was developed. The voltage major loop controller assures the sinusoidal output voltage and stabilizes the system. A deadbeat controller is used because both the current minor loop and the voltage major loop can use one sampling response. The validity of these techniques is confirmed by simulation studies. This method is expected to be useful for direct digital control of large-capacity sinusoidal voltage inverters using low-switching-frequency devices.

[307] L. H. Mweene, C. A. Wright, and M. F. Schlecht, "A 1 kw 500 khz front-end converter for a distributed power supply system," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 398-407, 1991.

The analysis, design, and performance of a prototype high-power-density converter suitable for use in the front-end of a distributed power supply system is presented. It delivers 1 kW to a regulated 40-V distribution bus from the rectified utility. Its switching frequency is 500 kHz, and it uses a phase-shifted PWM (pulsewidth modulation) technique to avoid primary side switching losses.

[308] R. Redl, N. O. Sokal, and L. Balogh, "A novel soft-switching full-bridge dc/dc converter: Analysis, design considerations, and experimental results at 1.5 kw, 100 khz," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 408-418, 1991.

The addition of an external commutating inductor and two clamp diodes to the phase-shifted PWM (pulsewidth modulated) full-bridge DC/DC converter substantially reduces the switching losses of the transistors and the rectifier diodes, under all loading conditions. The authors give analyses, practical design considerations, and experimental results for a 1.5-kW converter with 60-V, 25-A output, operating at 100-kHz clock frequency and 95% efficiency.

[309] C.-H. Yang, D. Y. Chen, C. Jamerson, and Y. P. Wu, "Stabilizing magamp control loop by using an inner-loop compensation," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 419-429, 1991.

Using an inner-loop compensation scheme, the order of the open-loop transfer function of a magamp control circuit is essentially reduced from two to one for a self-reset scheme. The problem normally associated with compensating a control transfer function with resonance peaking is thereby eliminated. Moreover, if the inner loop gain is designed high enough, the closed-loop gain can be insensitive to the variation of power circuit parameters such as saturable reactor permeability and capacitor equivalent series resistance (ESR). A design example is given to illustrate the step-by-step design procedure for a practical magamp control circuit. The results are verified by loop gain measurements.

[310] F. P. Dawson and P. Jain, "A comparison of load commutated inverter systems for induction heating and melting applications," IEEE Transactions on Power Electronics, vol. 6, no. 3, pp. 430-441, 1991.

A comparative analysis of a current source and a voltage source inverter suitable for induction heating and melting applications is presented. Both power supplies considered operate on the principle of load commutation. The comparison is based on criteria such as input power factor, component ratings, maximum and minimum operating frequencies, operation under varying load conditions, inverter starting capability, and system and control simplicity. The voltage source series resonant inverter is found to offer the best overall performance with respect to converter utilization.

[311] J. R. Laghari and W. J. Sarjeant, "Energy-storage pulsed-power capacitor technology," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 251-257, 1992.

Fundamentals of dielectric capacitor technology and multifactor stress aging of all classes of insulating media that form elements of this technology are addressed. The goal is the delineation of failure processes in highly stressed compact capacitors. Factors affecting the complex aging processes such as thermal, electromechanical, and partial discharges are discussed. Diagnostic measurement techniques available and those being developed to determine material degradation affecting available life and failure probability of capacitors are presented.

[312] D. G. Holmes and T. A. Lipo, "Implementation of a controlled rectifier using ac-ac matrix converter theory," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 240-250, 1992.

It is well known that a PWM-controlled rectifier can offer advantages of reduced low-order harmonics and unity input power factor when compared to a conventional thyristor converter. However, theoretically optimum PWM strategies are often difficult to implement physically or are not easily extended to regenerative operation. The authors propose an alternative PWM strategy based on AC-AC matrix converter theory, which generates only high-order switching harmonics, presents a unity power factor load to the supply, implicitly extends to regeneration (and operation with a center tapped DC output), and is feasible to physically implement for real-time output voltage control. Both the theory and physical simulation results are presented.

[313] A. Brambilla and E. Dallago, "Snubber circuits and losses of voltage-source gto inverters," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 231-239, 1992.

The power dissipation of series and parallel snubbers in gate turn-off thyristor (GTO) inverters is investigated. New circuits using optimized snubbers are simulated and compared and solutions that allow the recovery of the energy stored in the snubbers are reported. In particular, an inverter circuit that uses a transformer for the recovery of the energy trapped in the snubbers is investigated, and solutions that avoid saturation of the transformer core are studied.

[314] L. Rossetto and P. Tenti, "Using ac-fed pwm converters as instantaneous reactive power compensators," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 224-230, 1992.

A general control method that fully utilizes the inherent capability of AC-fed PWM converters to compensate for reactive and harmonic currents absorbed by other loads is presented. For this purpose, suitable definitions of instantaneous active and reactive current and power terms are introduced. Optimum modulation laws are then derived according to a general control theory valid for PWM multiconverter systems, which also results in maximum system efficiency. Simulated results demonstrate the capabilities of the proposed compensation method, which can also be implemented in existing systems as only modifications of the control section are needed.

[315] M. Steinbuch and O. Bosgra, "Dynamic modeling of a generator/rectifier system," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 212-223, 1992.

A nonlinear detailed model has been constructed for synchronous generators loaded with a rectifier bridge. This dynamic model is based on the description of the commutation and noncommutation stages. The switching instants depend on the state variables of the system. In order to be able to apply linear system theory for control design, an approximating linear model has been derived, based on application of the Floquet theory. Consequently, asymptotic stability analysis is possible with the linear model. Comparison with the full nonlinear model shows good resemblance.

[316] J. Holtz and J. O. Krah, "Adaptive optimal pulse-width modulation for the line-side converter of electric locomotives," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 205-211, 1992.

Two methods of generating synchronous online optimal PWM sequences for the line-side converter of electrical locomotives are described. The properties of the feeding supply line render the system oscillatory at multiple resonance frequencies, which are time-variable functions of the railway track topography and of the respective locations of traction vehicles. The prevailing topographic conditions define a time-variable virtual model of the overhead line, the harmonic energy of which is the optimum criterion to be minimized. The 176 switching instants of a nine-level PWM converter voltage are optimized using an online algorithm. The necessary computations are performed in the time intervals between two commutations. The performance is illustrated by measurements obtained from a real-time multiprocessing model of an extended railway track topography, including substations and locomotives. The developed hardware structure is designed for the implementation in a railway traction vehicle.

[317] M. Marchesoni, "High-performance current control techniques for applications to multilevel high-power voltage source inverters," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 189-204, 1992.

Several high-performance current control techniques are developed for applications to multilevel high-power voltage source inverters (VSIs). The logical sequence of the design choices is described, resulting in a very robust and reliable control system that allows an adequate switching optimization, excellent dynamic responses, and high accuracy in steady-state operation. The advantages of using various accessible DC potentials are fully exploited. The validity of the proposed schemes has been confirmed by digital simulations involving the generation of five-level voltage waveforms; however, the current control strategies developed can easily be extended to any multilevel inverter structure, even in the case of n-level voltage waveforms and three-phase systems.

[318] R. W. De Doncker and A. A. Vandenput, "A two-dimensional fft algorithm for three-phase inverter-fed systems," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 181-188, 1992.

A spectrum analyzer for three-phase inverter-fed balanced systems which is capable of calculating up to 24 harmonic components of the line currents every 130 μs is presented. The method is based on a synchronized sampling technique and on a highly efficient fast Fourier transform (FFT) for three-phase systems. The latter consists of a two-dimensional six-point discrete Fourier transform (DFT) followed by a two-dimensional four-point DFT. The total FFT algorithm has been successfully implemented on a TMS32010 digital signal processor.

[319] P. N. Enjeti and W. Shireen, "A new technique to reject dc-link voltage ripple for inverters operating on programmed pwm waveforms," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 171-180, 1992.

A proposal for rejecting DC-link voltage ripple in inverters operating on programmed PWM waveforms is examined in detail. It is demonstrated how continuous elimination of harmonics is achieved at the inverter output while simultaneously rejecting the DC-link voltage ripple. Thus, with the proposed technique, high-quality voltage is guaranteed at the inverter output terminals even with a substantial low-frequency voltage ripple on the DC-link. A thorough modeling of this technique along with the tradeoffs involved in acquiring the immunity to DC-link ripple is illustrated in detail. Potential applications of the technique are in fixed and variable frequency inverters for power supplies and AC motor drives that experience voltage ripple in the DC link such as when fed from a weak AC system that is frequently unbalanced. A design procedure along with the digital implementation of the proposed technique is described. Selected results were verified experimentally on a laboratory inverter.

[320] S. B. Taib, L. N. Hulley, Z. Wu, and W. Shepherd, "Thyristor switch model for power electronic circuit simulation in modified spice 2," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 568-580, 1992.

Modifications to the commercially available SPICE 2 program that allow the accurate simulation of thyristor circuits are discussed. A near-ideal switch model of a thyristor is developed using resistive components, thus eliminating the problems associated with transistor models. The simulator SPICE 2G.6 is modified and a new input format for the thyristor is implemented. Examples of simulations with the new model agree closely with theoretical and experimental investigations.

[321] L. D. Varga and N. A. Losic, "Synthesis of zero-impedance converter," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 152-170, 1992.

A method for synthesizing a system that converts a finite value of an impedance to zero, with an associated finite current and zero voltage, is presented. The synthesis method comprises positive current feedback of an exactly specified nature and value of its transfer function. The stability and dynamics of the system are controlled by an additional voltage loop. The zero-impedance converter is used to synthesize load-independent systems including (switch-mode) power converters and electric motor drive systems incorporating any kind of motor.

[322] S. Y. Erich and W. A. Polivka, "Input filter design criteria for current-programmed regulators," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 143-151, 1992.

The design of input filters for switched-mode regulators is discussed, and it is shown that the filter's effect on the power system depends on the control method used in the regulator's DC-DC converter. Design inequalities are reviewed for duty-ratio programmed converters, and specific expressions are presented for current-programmed converters. Examples of application to practical regulator circuits are given where current-programmed criteria, computer-driven measurement tools, and numerical evaluations of analytic expressions are used to design input filters.

[323] D. M. Sable, R. B. Ridley, and B. H. Cho, "Comparison of performance of single-loop and current-injection control for pwm converters that operate in both continuous and discontinuous modes of operation," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 136-142, 1992.

An analysis of current-injection-controlled (CIC) power converters operating in both the continuous and discontinuous modes is performed using the PWM switch model and a new, continuous-time model of CIC. The stability, output impedance, audio susceptibility, and transient response are compared with single-loop control. The control of an example buck converter is designed with CIC and single-loop control. It is shown how single-loop controlled power converters exhibit a large change in the dynamic performance when crossing the boundary between continuous mode and discontinuous mode. This is especially true for the output impedance and transient response. The dynamic performance of CIC power converters remains relatively fixed when crossing this boundary. A significant performance improvement can be realized when CIC is employed in converters that operate over a wide load range.

[324] V. Vlatkovic, J. A. Sabate, R. B. Ridley, F. C. Lee, and B. H. Cho, "Small-signal analysis of the phase-shifted pwm converter," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 128-135, 1992.

The specific circuit effects in the phase-shifted PWM (PS-PWM) converter and their impact on the converter dynamics are analyzed. The small-signal model is derived incorporating the effects of phase-shift control and the utilization of transformer leakage inductance and power FET junction capacitances to achieve zero-voltage resonant switching. The differences in the dynamic characteristics of the PS-PWM converter and its PWM counterpart are explained. Model predictions are confirmed by experimental measurements.

[325] S. Morrison, "Analysis of a hybrid series parallel resonant bridge converter," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 119-127, 1992.

The steady-state operation of a hybrid series parallel resonant bridge is analyzed. Two expressions are derived for the power output as a function of capacitor ratio, switching frequency, and conversion ratio. One power output expression is for conversion ratios less than or equal to one, and the other expression is for conversion ratios greater or equal to one and less than or equal to two. The optimum conversion ratio for maximum power transfer is also derived.

[326] J. B. Klaassens, M. P. N. van Wesenbeeck, and H. K. Lauw, "Series-resonant single-phase ac-dc power supply with control of reactive power," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 111-118, 1992.

It is shown that the resolution of the high-frequency input current of the series-resonant converter leads to the possibility of accurately controlling the waveform of the source current. In combination with the accurate positioning of the high-frequency current pulses, it is possible to influence the exchange of power with the source by introducing active filtering. A power factor equal to one would lead to optimal operation. However, the zero crossing of the AC source voltage introduces the need to store energy. Bulky low-frequency storage elements increase the specific volume and weight of the converter, while the exchange of energy with storage elements decreases the overall efficiency. The energy stored in the resonant circuit is fundamentally too low to solve this problem. The stored energy in the output capacitor necessary to decrease the high-frequency ripple voltage is available for these purposes. To meet the optimal conditions for the power factor at the source, a bipolar flow of energy is required.

[327] W.-J. Gu and K. Harada, "A circuit model for the class e resonant dc-dc converter regulated at a fixed switching frequency," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 99-110, 1992.

An averaging circuit model is developed for the class E resonant DC-DC converter regulated at a fixed switching frequency. The regulation is achieved by use of an auxiliary switch. The model is obtained based on the circuit analysis using the Fourier series expansion. Steady-state and small-signal dynamic analysis is presented, which reveals that the DC output is well controlled by the control angle of the auxiliary switch and that there exists a right-half-plane zero in the control-to-output transfer function. The analysis results are verified by the experiments.

[328] R. P. Severns, "Topologies for three-element resonant converters," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 89-98, 1992.

Many of the limitations of two-element resonant topologies can be overcome by adding a third reactive element. However, using three elements greatly increases the number of possible topologies, making it very difficult to explore this class of circuits on a trial-and-error basis. An orderly search procedure that exposes a large number of new topologies, many of which are resonant and have useful properties, is presented.

[329] P. Maranesi, "Small-signal circuit modeling in the frequency-domain by computer-aided time-domain simulation," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 83-88, 1992.

The possibility of obtaining the frequency-domain dynamic model of a circuit from transient analysis data provided by a circuit simulator is shown. The computer-aided design (CAD) program FREDOMSIM, which governs the simulations, processes the output data, and supplies the results in a well suited manner for design optimization, is introduced. Feedback circuits are modeled with all their feedback loops open, so that the designer can optimize systems by proper a posteriori loop closures. The characterization with the loops closed is also given.

[330] L. Garcia de Vicuna, A. Poveda, L. Martinez, F. Guinjoan, and J. Majo, "Computer-aided discrete-time large-signal analysis of switching regulators," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 75-82, 1992.

A computer program based on a general nonlinear discrete formulation procedure for large-signal analysis of switching regulators is introduced. The program provides both time-domain and state-trajectory simulation of converter state variables under different control strategies in either of two conduction modes. As a result, the regulator asymptotic stability can be predicted for large-signal operation. Experimental results verify the theoretical predictions.

[331] A. F. Goldberg and M. F. Schlecht, "The relationship between size and power dissipation in a 1-10 mhz transformer," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 63-74, 1992.

The tradeoff between size and power dissipation in the design of low-profile 1-10-MHz transformers with planar spiral windings is considered. For a fixed power loss and number of conductor layers, the transformer with the smallest possible footprint can be designed by a trade-off of core and copper loss. The relationship between the marginal reduction of the transformer footprint and the associated marginal increase in power dissipation and/or number of conductor layers for the design of the smallest possible transformer is discussed.

[332] D. C. Hamill, J. H. B. Deane, and D. J. Jefferies, "Modeling of chaotic dc-dc converters by iterated nonlinear mappings," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 25-36, 1992.

In parameter ranges where conventional methods break down, DC-DC converters may be described by iterated mappings, a nonlinear discrete modeling technique. The underlying principles are explained and are applied to the example of a PWM-controlled buck converter. Stable behavior and bifurcations to chaos are predicted by numerical evaluation of the governing mapping and are confirmed by experiment.

[333] A. Ghahary and B. H. Cho, "Design of transcutaneous energy transmission system using a series resonant converter," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 261-269, 1992.

A full-bridge zero-voltage-switched series resonant converter that transfers 12-48 W of regulated power across a large, variable air gap has been designed and built. This converter can power an artificial heart through intact skin by utilizing a transformer with an air gap of 1-2 cm between the primary and the secondary. The secondary winding would be implanted under the skin, and the primary would be placed on top of the secondary outside the body.

[334] R. S. Wallace and D. G. Taylor, "A balanced commutator for switched reluctance motors to reduce torque ripple," IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 617-626, 1992.

A method of computing the reference currents for current tracking feedback control, called a balanced commutator, is presented. For a given motor, this commutator reduces the peaks and the rates of change of the reference currents. Although primarily intended for lower-speed direct-drive applications, the commutator design allows accurate current tracking, and therefore reduced torque ripple, over a reasonably wide range of operating speeds. Three motor models, analytical, numerical, and measured, are considered. Issues relating commutation schemes to amplifier requirements are addressed by simulating simple analytical models of the electrical dynamics. To reveal the interplay between motor design and commutator output, torque models produced by numerical field calculations are considered. To demonstrate the practical benefits and limitations of the method, a balanced commutator based on measured motor data is implemented, and torque ripple reduction is quantified in a laboratory experiment.

[335] A. Khambadkone and J. Holtz, "Low switching frequency and high dynamic pulsewidth modulation based on field-orientation for high-power inverter drive," IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 627-632, 1992.

In megawatt-rated inverter-fed induction motor drive systems, the gate-turn-off (GTO) switching losses account for a considerable amount of the total losses. hence, the switching frequency in such systems must be kept at a low value of only a few hundred hertz. To avoid undesired torque harmonics under such operating conditions, the pulse control of the inverter is made dependent on the orientation of the rotor flux of the drive machine. This method transfers a major portion of the unavoidable current distortions into the field axis where they have no influence on the machine torque. An optimal trajectory-oriented control is presented that achieves low switching frequency at low torque and current harmonics and exhibits a very fast dynamic response. The performance of this method is demonstrated by measured results from a 30-kW model drive.

[336] M. H. Kheraluwala, D. W. Novotny, and D. M. Divan, "Coaxially wound transformers for high-power high-frequency applications," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 54-62, 1992.

Design considerations for transformers utilized in high-power high-frequency DC/DC converters are addressed. Major areas of concern are core-material selection, minimization of copper losses due to skin and proximity effects, and the realization of controlled leakage inductances. Coreless characteristics for various high-frequency materials are presented, and the influence of various conventional winding arrangements on the copper losses and leakage field is also demonstrated. Coaxial winding techniques (used commonly in high-frequency transformers) are next investigated as a feasible solution for containing the leakage flux within the interwinding space, thus preventing it from permeating the core and resulting in lower core losses and the avoidance of localized heating. Added benefits of this technique are reduced forces within the transformer, lower copper losses, and robust construction. The performances of two experimental single-phase 50-kW, 50-kHz units are reported. A three-phase version of coaxially wound transformers is also presented.

[337] R.-S. Lai, K. D. T. Ngo, and J. K. Watson, "Steady-state analysis of the symmetrical push-pull power converter employing a matrix transformer," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 44-53, 1992.

Data published for the symmetrical push-pull power converter (SPPPC) show that the matrix transformer and the cross-coupling capacitors in this buck-type topology introduce unusual waveforms and properties. Circuit operation is examined in order to seek a simplified explanation of the published observations. Steady-state performance is analyzed and design equations are developed using state-space averaging. It is found that the SPPPC is equivalent to the conventional push-pull converter with an input filter as far as steady-state behavior and voltage/current ripple are concerned. Despite the presence of the cross-coupling capacitors, the currents in the primary windings in series with the same switch are identical. The rms current in the primary windings of the SPPPC is lower than that in the conventional push-pull converter.

[338] S. Singer and R. W. Erickson, "Canonical modeling of power processing circuits based on the popi concept," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 37-43, 1992.

The fundamental power-processing properties of switching converter circuits are modeled using generalized power-conservative (POPI) networks. Depending on the application, it may be most appropriate to model the first-order converter properties as those of an ideal transformer, gyrator, loss-free resistor, or other POPI network. These basic functions can be obtained either through selection of a topology that naturally possesses the desired characteristics or by addition of a suitable control network. Some well-known converter topologies are shown to behave naturally as gyrators, loss-free resistors, and constant power networks. The application of the gyrator to network two voltage sources and the use of the loss-free resistor as a unity power factor rectifier are described.

[339] S. R. Sanders and G. C. Verghese, "Lyapunov-based control for switched power converters," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 17-24, 1992.

Beginning with fundamental properties such as passivity or incremental passivity of the network elements comprised by a switched power converter, the nominal open-loop operation of a broad class of such converters is shown to be stable in the large via a Lyapunov argument. The obtained Lyapunov function is then shown to be useful for designing globally stabilizing controls that include adaptive schemes for handling uncertain nominal parameters. Numerical simulations illustrate the application of this control approach in DC-DC converters.

[340] B. K. Bose, "Recent advances in power electronics," IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 2-16, 1992.

Recent advances in several key areas of power electronics technology, such as power semiconductor devices, power converter circuits, and control of power electronics, are discussed. The structure and characteristics of IGBT, SIT, SITH, and MCT devices are reviewed. The principal converter types and their recent trends are described. A brief review of power integrated circuits is included. The features of microcomputer and VLSI control are described, and recent advances in microcomputers are highlighted. The principles of expert systems, fuzzy control, and neural networks are presented.

[341] M. K. Kazimierczuk and S. Wang, "Frequency-domain analysis of series resonant converter for continuous conduction mode," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 270-279, 1992.

Most previous analyses of a series resonant DC-DC converter (SRC) have been performed in the time domain. A comprehensive frequency-domain analysis of the SRC for steady-state operation, along with experimental results is presented. Simple analytical design equations are derived for the basic performance parameters of the converter operating in the continuous conduction mode (CCM) using Fourier series techniques and a high-Q_L assumption. Three types of class-D current-driven rectifiers are considered. The diode threshold voltage and forward resistance as well as the ESR of the output filter capacitor are taken into account. Experimental results were in good agreement with theoretical predictions.

[342] J. H. Ko, S. S. Hong, M. G. Kim, and M. J. Youn, "Modeling and improved current control of series resonant converter with nonperiodic integral cycle mode," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 280-288, 1992.

A dynamic modeling and an improved current control technique for a series resonant converter with nonperiodic integral cycle mode are proposed to overcome the disadvantages of an integral cycle mode-controlled series resonant converter. The internal operational characteristics are investigated in detail and an improved current control technique is developed based on this analysis. Using the proposed control technique, the minimized current ripple with reduced offset current and the fast transient response with negligible overshoot can be obtained. Furthermore, the continuous output voltage levels can also be available by accurately controlling the average filter input current. The usefulness of the proposed technique is verified through computer simulations and experiments.

[343] S. Sooksatra and C. Q. Lee, "Pwm-controlled src with inductive output filter at constant switching frequency," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 289-295, 1992.

By using the PWM control scheme in the series resonant converter with with inductive output filter, the converter can be operated at a constant frequency. This converter has lower switching loss than the PWM converter and better control characteristics than the ordinary SRC. Since the peak current in the present converter equals the load current, it has the lowest possible peak current stress among converters. The analysis and the performance characteristics of the converter operating at a constant switching frequency are presented. Experimental results are given to confirm the analytical work.

[344] Y. G. Kang and A. K. Upadhyay, "A parallel resonant converter with postregulators," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 296-303, 1992.

A parallel resonant converter (PRC) with postregulator(s) synchronized to the primary switching frequency is investigated for discontinuous-conduction mode operation. It is analyzed with a magnetic amplifier, which blocks the rising edge of the secondary voltage, and with a synchronized buck regulator, which blocks part of the trailing edge of the secondary voltage waveform under the steady-state conditions. As a result, it has been shown that magnetic amplifiers are not suitable for resonant mode power converters, since the step change of the load from low to high during the same switching period as the primary makes the operating conditions worse. However, postregulators that block the trailing edge of the secondary voltage waveform do not adversely affect the operating conditions of PRC and work satisfactorily. As an alternative, a PRC with a magnetic postregulator is presented. An offline 150-W 250-kHz PRC is designed with a magnetic postregulator for a personal computer application, and experimental waveforms are included.

[345] M. J. Schutten, R. L. Steigerwald, and M. H. Kheraluwala, "Characteristics of load resonant converters operated in a high-power factor mode," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 304-314, 1992.

The performance of the parallel resonant converter and the combination series/parallel resonant converter (LCC converter) when operated above resonance in a high power factor mode are determined and compared for single-phase applications. When the DC voltage applied to the input of these converters is obtained from a single-phase rectifier with a small DC link capacitor, a relatively high power factor inherently results, even with no active control of the input line current. This behavior is due to the pulsating nature of the DC link and the inherent capability of the converters to boost voltage during the valleys of the input AC wave. With no active control of the input line current, the power factor depends on the ratio of operating frequency to tank resonant frequency. With active control of the input line current, near-unity power factor and low-input harmonic currents can be obtained.

[346] C. Broche, J. Lobry, P. Colignon, and A. Labart, "Harmonic reduction in dc link current of a pwm induction motor drive by active filtering," IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 633-643, 1992.

Substitution for DC motors by pulsewidth modulation (PWM) inverter-fed induction motors in railways supplied by DC voltage leads to high harmonic levels in the overhead line current. This results in interference in the signaling systems. In order to satisfy the requirements of Belgian railway operators, the problem of the harmonic reduction in overhead line current has been addressed. An active filtering system seemed the best solution to this problem. Consequently, a feedback filtering system was developed. It includes a power amplifier feeding a transformer, which reinjects a voltage signal in DC line to reduce robustness harmonics; this signal is proportional to the overhead line current itself. The experimental results on 100-kW equipment proved the performance of the system: the harmonic reduction is effective in the required frequency range in both steady-state and transient conditions.

[347] T. C. Green and B. W. Williams, "Spectra of delta-sigma modulated inverters: An analytical treatment," IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 644-654, 1992.

Analytic expressions for the output voltage spectrum of an asynchronous delta (or delta-sigma) modulated inverter are reported and supported by experimental data. The analysis yields three functions that give the frequency, phase, and amplitude of each component of the spectrum. These functions are in terms of the sinusoidal reference waveform and the properties of the modulator. The method provides greater accuracy and computational efficiency than the numerical methods reported to date. The spectral components form pairs of sidebands around multiples of the average switching frequency. The functions detail the relationship between the number of significant sideband components and the depth of modulation and illustrate the spread-spectrum nature of delta modulation. Extensions to nonsinusoidal reference waveforms and to hysteresis current controllers are considered.

[348] A. H. Weinberg and L. Ghislanzoni, "A new zero voltage and zero current power-switching technique," IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 655-665, 1992.

Work on a new converter topology whose advantage is that the power switching occurs at both zero current and zero voltage, giving it major advantages over the present state of the art, is reported. The application of this topology to both high- and low-output voltage converters is described in detail. Design details and test results are given, together with a full analysis of the operation of the converters.

[349] J.-C. Li and G.-C. Hsieh, "Analysis of the boost zero-current-switched quasi-square-wave converter," IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 673-682, 1992.

The steady-state analysis of the boost zero-current-switched quasi-square-wave converter (ZCS-QSC) is presented. The normalized output current and voltage characteristic is plotted using the switching frequency as the parameter. The small-signal equivalent circuit is derived based on a per unit system. An amplifier load is given to stimulate the actual load perturbation.

[350] G. B. Joung, J. G. Cho, and G. H. Cho, "A generalized quantum resonant converter using a new quantum resonant module," IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 666-672, 1992.

For the generalization of quantum resonant converters, new quantum resonant modules, which are a quantum series resonant module (QSRM) and a quantum parallel resonant module (QPRM), are proposed. The QSRM and QPRM are modeled as an equivalent inductor and an equivalent capacitor, respectively. The models of the proposed modules are useful in deriving the practical family of quantum resonant converters corresponding to the conventional PWM converters. The AC/AC quantum resonant converters are investigated as useful converters. The concept of modules and the validity of the modeling are confirmed by the experiment.

[351] P. J. Wolfs, K. C. Kwong, and G. F. Ledwich, "A single-phase converter with a high-frequency current-sourced link," IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 683-692, 1992.

Duality relationships that have proved useful in the development of DC-DC converter topologies are applied to existing voltage stiff high-frequency link force-commutated converters. This new area of application of the duality concept results in the development of new current stiff link converters that retain the advantages of current fed DC-DC converters. The requirements on the converters enforced by the need for instantaneous balance of input and output powers are examined. A current control technique has been developed that controls the charge delivered to the load during each switching cycle. This allows a wide bandwidth voltage regulator to be applied. Finally, the results obtained with a low-power prototype and a reactive load are presented. The new converter requires only four power MOSFETs and relatively simple controls and is reversible.

[352] P. Jain and S. B. Dewan, "Analysis and design of a high-frequency high-power series resonant inverter using asymmetrical thyristors," IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 693-706, 1992.

The description, analysis, and design of a high-frequency series inverter are presented. A detailed analysis is given that includes the effect of di/dt inductor and snubber components. Steady-state characteristics of the inverter are presented, and equivalent circuits and expressions to determine switching transients are derived. A design example of a 150-kW, 50-kHz inverter is presented to illustrate the design of a high-frequency series resonant inverter. Finally, the experimental verification of theoretical results is provided.

[353] P. Tenti, L. Malesani, and L. Rossetto, "Optimum control of n-input k-output matrix converters," IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 707-713, 1992.

Significant developments of the general optimum control theory presented in a previous paper by the authors (1988) are discussed for the specific case of multiphase matrix converters. Results hold, regardless of system configuration, input and output voltage waveforms, and loads. Applications to the most practical converter structures are illustrated, and implementation criteria of the optimum control method are derived. Simulated results confirm the flexibility and effectiveness of the approach.

[354] J. A. Ferreira, A. van Ross, and J. D. van Wyk, "A generic soft switching converter topology with a parallel nonlinear network for high-power application," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 324-331, 1992.

A soft switching concept that derives from the resonant link and resonant pole converters and combines the best features of resonant and hard switching converters is applied to a phase arm. The inductor of the resonant LC is designed to saturate, thus having effectively two inductance values: a very large value during the conduction period and a small value that is only active during switching. The advantage of this technique is that a resonant tank with smaller continuous ratings can be used without giving up the component count advantage of resonant converters. Another feature, contrary to other resonant topologies, is that semiconductor switches need not be overdimensional for voltage and current rating.

[355] A. W. Kelley and W. F. Yadusky, "Rectifier for minimum line-current harmonics and maximum power factor," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 332-341, 1992.

Rectifier line-current harmonics interfere with proper power system operation, reduce rectifier power factor, and limit the power available from a given service. The rectifier's output filter inductance determines the rectifier line-current waveform, the line-current harmonics, and the power factor. Classical rectifier analysis usually assumes a near-infinite output filter inductance, which introduces significant error in the estimation of line-current harmonics and power factor. A quantitative analysis of single- and three-phase rectifier line-current harmonics and power factor as a function of the output filter inductance is presented. For the single-phase rectifier, one value of finite output filter inductance produces maximum power factor and a different value of finite output filter inductance produces minimum line-current harmonics. For the three-phase rectifier, a near-infinite output filter inductance produces minimum line-current harmonics and maximum power factor, and the smallest inductance that approximates a near-infinite inductance is determined.

[356] E. P. Wiechmann, J. R. Espinoza, and J. L. Rodriguez, "Compensated carrier pwm synchronization: A novel method to achieve self-regulation and ac unbalance compensation in ac fed converters," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 342-348, 1992.

The compensated carrier PWM synchronization (CCPS) method for AC-fed PWM converters is presented. The method provides a solution to PWM converters fed by industrial power systems (IPSs). Such environments usually present unbalances and magnitude fluctuations of AC voltages. Those circumstances impair standard PWM techniques because low-order harmonics are produced and DC-link regulation is poor. To reduce these undesirable effects produced by IPS, a method based on using independently compensated carriers per phase was conceived. In particular, CCPS prevents second harmonic generation and achieves converter self-regulation. The method can be used with any PWM technique and bidirectional power flow. The evaluation of CCPS is based on a complete performance comparison of a PWM rectifier with and without CCPS for various known PWM techniques.

[357] C. K. Tse and K. M. Adams, "Quasi-linear modeling and control of dc-dc converters," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 315-323, 1992.

A quasi-linear approach is proposed for modeling and control of DC-DC converters. The method presented is derived by perturbing an approximate large-signal equation around a varying operating point in a reduced variable space. This differs from the usual practice of applying the perturbation technique around a fixed operating condition. In the proposed algorithm, the control equation and the control parameter are constantly adjusted according to environmental changes to meet the specified dynamical requirement.

[358] L. Calderone, L. Pinola, and V. Varoli, "Optimal feed-forward compensation for pwm dc/dc converters with 'linear' and 'quadratic' conversion ratio," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 349-355, 1992.

An analytical procedure to optimize the feedforward compensation for any PWM DC/DC converters is described. Achieving zero DC audiosusceptibility was found to be possible for the buck, buck-boost, Cuk, and SEPIC cells; for the boost converter, however, only nonoptimal compensation is feasible. Rules for the design of PWM controllers and procedures for the evaluation of the hardware-introduced errors are discussed. A PWM controller implementing the optimal feedforward compensation for buck-boost, Cuk, and SEPIC cells is described and fully experimentally characterized.

[359] S.-Z. Dai, N. Lujara, and B.-T. Ooi, "A unity power factor current-regulated spwm rectifier with a notch feedback for stabilization and active filtering," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 356-363, 1992.

A stand-alone, unity power factor, current-regulated sinusoidal pulsewidth modulated (SPWM) rectifier is described. The topology is based on the series connection of three four-valve single-phase bridges, which allows the conventional two-stage logic SPWM strategy to be used without interphase interference. The problems of stability and low harmonic waveform distortion are identified. Solutions are found by using a simple local notch filter feedback circuit that fulfills the dual function of stabilizing and active filtering. From the clarification given by this more expensive but less constrained topology, the stage is set for the next step in incorporating the lessons learned to the more economical topology based on the six-valve, three-phase parallel bridge, which requires a tristate logic for PWM control when operating in the current-source configuration.

[360] G. Fregien and J. D. van Wyk, "Nonlinear capacitors in snubber circuits for gto thyristors," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 425-429, 1992.

Many applications with GTO thyristors require snubber circuits, at least for turn-off. In achieving high switching frequencies there are conflicting design criteria for the snubber capacitor-losses versus timing conditions. Improvements to this situation are expected by employing nonlinear capacitors. Features of snubber circuits with nonlinear capacitors are described, and experimental results obtained from 50-A and 90-A GTO thyristors are discussed.

[361] D. S. Oh, K. Y. Cho, and M. J. Youn, "A discretized current control technique with delayed input voltage feedback for a voltage-fed pwm inverter," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 364-373, 1992.

A current control technique for a voltage-fed PWM inverter is presented. The discretized state equation of an inverter and a load independent of operating conditions with the delayed input voltage feedback has been derived using the averaging concept. The discretized current controller is proposed to reduce the current error as fast as possible using the deadbeat control strategy and to stabilize the closed-loop system asymptotically when the variations of load parameters are given in the predetermined stabilized region. This proposed control scheme is realized by the symmetrical uniform sampling method and is easily implemented using a microprocessor-based system. The computer simulation for the proposed controller has been done and the results show the good static and dynamic performances.

[362] S. D. Freeland, "Techniques for the practical application of duality to power circuits," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 374-384, 1992.

Techniques that simplify the application of duality to power circuits are presented. Duals are derived for ideal switches (including two- and four-quadrant switches and semiconductor-controlled rectifiers (SCRs), transformers and coupled inductors, and capacitors. A collection of common topological structures and corresponding duals is also given. This library of dual relations allows even complicated circuits to be transformed, primarily by substitution.

[363] A. Cheriti, K. Al-Haddad, L. A. Dessaint, T. A. Meynard, and D. Mukhedkar, "A rugged soft commutated pwm inverter for ac drives," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 385-392, 1992.

A novel DC-DC converter for variable-speed AC drives using the zero-voltage switching technique is described. This converter combines the advantages of soft commutated inverters and those of conventional pulsewidth modulated (PWM) inverters. In the proposed scheme, the soft commutation reduces the constraints on the switches, and the PWM enables simple and efficient regulation of the power flow. Furthermore, the zero-voltage switching technique makes operation safe, and switching bipolar transistors at 20 kHz is easily achieved without compromising the efficiency of the system.

[364] W. C. Karl, S. B. Leeb, L. A. Jones, J. L. Kirtley, and G. C. Verghese, "Applications of rank-based median filters in power electronics," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 437-443, 1992.

A class of robust, rank-based signal processing filters is considered, particularly with regard to its usefulness in the power electronics field. This class of nonlinear filters is characterized by the inclusion of a sorting element in the signal path. The sorting operation allows these filters to suppress impulsive noise while preserving edges and monotonic sections of signals. This introductory work concentrates primarily on the median filter, it being the most accessible filter of the class. A working knowledge of issues arising in design and implementation is developed.

[365] L. D. Salazar and P. D. Ziogas, "A novel current-assisted output voltage control technique for switch-mode-rectifier converters," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 444-452, 1992.

A current-assisted voltage control technique for high-power switch-mode-rectifier (SMR) converters is proposed. This technique implements a fast-forward AC current loop by sensing the current through the output filter capacitor. The control loop forces the AC current component of the output filter inductance to be synchronized with a symmetrical triangular reference waveform. As a result, the converter behaves like a fixed-frequency current-regulated voltage source with a low-output impedance and an increased bandwidth. A small-signal linear model is derived and the dynamic performance of a buck-derived SMR using the proposed control technique is analyzed. Simulation and experimental results are presented.

[366] S. A. Streng and R. J. King, "Ripple feedback for the resonant-filter unity-power-factor rectifier," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 453-461, 1992.

An unusual bucklike unity-power-factor rectifier with a resonant load-balancing network permits current-limited operation down to zero output voltage in a single-stage topology. However, this rectifier has been found to be sensitive to AC-line voltage distortion and is potentially unstable with realistic values of AC-line impedances. A new ripple feedback is proposed that solves both problems. A large-signal time-varying analysis is given along with incremental, quasi-static, and low-frequency approximations. Experimental verification is provided by a 500-W 500-kHz rectifier operating from the 120-V, 60-Hz distribution system.

[367] R. Liu and C. Q. Lee, "Series resonant converter with third-order commutation network," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 462-468, 1992.

To compensate for the poor output voltage regulation of the series resonant converter (SRC), a converter is derived by adding an inductor in parallel with the resonant capacitor of the conventional SCR. The resulting converter is called the LLC-SRC. This converter is analyzed via a two-dimensional state-plane diagram through a proper transformation of its state variables. Based on the analysis results, a set of characteristic curves is derived showing that the control characteristics and component stresses of the new converter are improved compared with those of a conventional SRC. Based on these curves, the design procedure for the LLC-SRC is formulated. The experimental results from a breadboard model were used to verify the theoretical work.

[368] D. S. Lo, C. P. Henze, and J. H. Mulkern, "A compact dc-to-dc power converter for distributed power processing," IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 714, 1992.

The authors present a compact (55-W/in³), efficient (86% power train), 1-MHz switch-mode, DC-to-DC power converter contained in a 2-in by 2-in by 0.25-in, 1-in³ package. They describe the interleaved forward topology, steady-state analysis, switch transitions, capacitor substrate, planar printed-wiring-board transformer, packaging, electrical performance, power loss analysis, thermal analysis, reliability, and efficiency and power density improvements.

[369] Y. Jang and R. W. Erickson, "Physical origins of input filter oscillations in current programmed converters," IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 725-733, 1992.

Addition of an input filter to a current-programmed converter can cause the controller to oscillate. Two instability mechanisms can typically occur: 1) the current programmed controller effective current feedback loop may become unstable, or 2) the controller effective input voltage feedforward loop, which becomes a positive feedback loop when an input filter is added, may oscillate. Three design criteria for preventing oscillations are derived and interpreted. When all three criteria are well satisfied, then the output voltage regulation loop gain is unchanged. Hence, input filters of current programmed converters can be designed in essentially the same manner as for duty-ratio programmed converters. Results are summarized in tabular form for the basic buck, boost, and buck-boost converters. Experimental measurements for a buck converter with different input filters support the theoretical predictions.

[370] C. H. Xu and D. Schroder, "A power bipolar junction transistor model describing static and dynamic behavior," IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 734-740, 1992.

The power bipolar junction transistor (PBJT) is investigated and modeled. Particular interest is concentrated on the injection charge in the collector layer that dominates the large-signal characteristics of the device. Based on the semiconductor physics, ordinary differential equations describing the injection charge are derived. These equations take into account the recombination, charging, and discharging processes in the collector layer. A network model for the PBJT is derived by adding these equations to a standard model. This model is implemented in the IG-SPICE language. The static behavior, such as the quasi-saturation, and the dynamic behavior, including turn-off under the 'stong drive' condition, can be simulated and analyzed. The simulation correlates well with the measurement.

[371] Y. Iwaji and S. Fukuda, "A pulse frequency modulated pwm inverter for induction motor drives," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 404-410, 1992.

A PWM pulse pattern optimization method using pulse frequency modulation (PFM) is described. In conventional PWMs the pulse frequency is kept constant. In the proposed PFM, however, the pulse frequency is adjusted. The PFM technique is intended to not only reduce the magnetic acoustic noises of driven motors but also to improve the performance of sinusoidal inverters. The PWM pulse patterns are basically controlled so that the time-integral function of the voltage vectors in the space vector notation may draw a circular locus. In addition to this, the pulse frequency, of PWM is also controlled so that the performance index, which represents the degree of achieved objectives, may be minimized. Two PIs, one for minimizing the distortion of output currents and the other for minimizing the torque pulsation of driven motors, are employed. The method is implemented using a single-chip microprocessor, and the experimental results demonstrate its validity.

[372] C.-M. Liaw, K.-H. Chao, and F.-J. Lin, "A discrete adaptive field-oriented induction motor drive," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 411-419, 1992.

A discrete model reference adaptive controller (MRAC) is designed and implemented. This MRAC makes the performance of the field-oriented induction motor drives insensitive to parameter changes. Only the information of the reference model and the plant output are required. Hence, the proposed controller is easy to implement practically. For designing the proposed adaptive controller, the dynamic model of the drive system is estimated from the sampled input-output data using the stochastic modeling technique. The theoretical basis of the adaptive control is derived and simulation is made. The hardware of the drive system and the microprocessor-based adaptive controller are discussed. Some experimental results are given to demonstrate the effectiveness of the proposed controller.

[373] M. Kanter, S. Singer, R. Cerny, and Z. Kaplan, "Multikilojoule inductive modulator with solid-state opening switches," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 420-424, 1992.

A four-stage inductive storage XRAM (inverse MARX) circuit was used to amplify current and power. By means of switching action, individual inductors are charged in series and discharged in parallel to the load. A microprocessor controls the timing of the switches, which results in a predetermined load current waveform. The use of present asymmetric GTOs at much higher currents than rated allowed the amplification and shaping of a 2.5-kA charging current to 9.6 kA at the load. An energy of 25 kJ was transferred to the load, yielding 84% efficiency. The losses were mainly due to the winding resistance of the inductors. With the best-performance commercially available GTOs, this circuit may deliver over 100 kJ with energy density of 1.6 kJ/kg. Simulation and experimental results are presented.

[374] M. Pietrzak-David, B. de Fornel, A. M. Nogueira Lima, and K. Jelassi, "Digital control of an induction motor drive by a stochastic estimator and airgap magnetic flux feedback loop," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 393-403, 1992.

An approach for the problem of airgap flux estimation in induction motors is presented. The Kalman filter algorithm is developed to provide an estimated state-vector containing flux linkage components. The estimated fluxes are then used to implement a direct flux control loop through an inverter-fed AC drive scheme. The overall control system is developed around a digital unit based on a 16-b microprocessor and a signal processor.

[375] R. Dutta and A. Rothwarf, "Design considerations for p-i-n thyristor structures," IEEE Transactions on Power Electronics, vol. 7, no. 2, pp. 430-435, 1992.

An analysis of a high-voltage gate turn-off (GTO) thyristor structure with a double-layered n base (p-i-n structure) is presented. From integration of Poisson's equation, an expression for the forward-blocking voltage at the onset of avalanche breakdown is obtained. Simple design criteria are developed to calculate the optimal thickness and doping density of the n base of a conventional pnpn structure designed for a specific voltage-blocking capability. The same principle is applied to design for the doping densities and thicknesses of the high-resistivity region and the buffer layer of the p-i-n GTO structure. The forward-blocking voltage, as well as the on-state voltage (at a current density of 300 A cm^-2) is predicted for a wide range of base layer thicknesses and doping densities to illustrate the available tradeoff options. Lowest on-state power dissipation for high blocking voltages (gt;6000 V) is predicted for a doping level of 5 × 10¹² cm^-3 in the high-resistivity layer.

[376] C. R. Kohut, "Input filter design criteria for switching regulators using current-mode programming," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 469-479, 1992.

Design criteria are developed for a constant-frequency current-programmed switching DC-to-DC converter with an input filter to ensure stability and prevent performance degradation. The criteria are given in terms of the filter voltage transfer function H_s, output admittance Y_s, and the y-parameter model of the switching converter. The criteria as listed as four inequalities and illustrated graphically. The criteria may be summarized as follows: assuming a converter that satisfies its loop gain T, line-to-output transfer function A_gf, and output impedance Z_of requirement is given, an input filter with H_s and Y_s can be used to attenuate the noise emissions from the converter without adversely affecting the converter if H_s <= 1 (may be relaxed to 3-6 dB), and Y_s is larger than the curves of the graphical illustration, perhaps using 6 dB as a rule-of-thumb minimum separation.

[377] W. G. Dunford and J. D. van Wyk, "Harmonic imbalance in asynchronous pwm schemes," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 480-486, 1992.

The harmonic content (both integral and nonintegral) of an asynchronous three-phase PWM (pulse width modulated) scheme is analyzed. It is shown that in a three-phase inverter with asynchronous modulation the nonintegral line currents produced form unbalanced sets. The percentage imbalance for a particular order is a function of the harmonic order only. No attempt has been made here to analyze the effect of harmonic imbalance in a load such as an induction motor. However, for practical frequency ratios the absolute amplitude of the current imbalance is small due to the small amplitude of the nonintegral components. More significant changes occur in the balanced integral orders due to small changes in frequency ratio.

[378] J. K. Steinke, "Switching frequency optimal pwm control of a three-level inverter," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 487-496, 1992.

A pulse-width-modulation (PWM) method for the control of a three-level inverter is described. The switching frequency optimal-PWM method (SFO-PWM) works with a constant carrier frequency not synchronized with fundamental stator frequency. SFO-PWM gives an optimal utilization of the mean thyristor switching frequency permitted; therefore, PWM carrier frequency may be chosen to a value of two times the permitted mean thyristor switching frequency. The signal processing structure is simple. Many applications of three-level inverter work with a DC-link neutral point not stabilized from the power input converter. A neutral-point potential control is described, which is capable of stabilizing potential by varying the switching sequences of the three-level inverter itself. Results from computer simulation and practical experience show the good performance of SFO-PWM.

[379] G. Carrara, S. Gardella, M. Marchesoni, R. Salutari, and G. Sciutto, "A new multilevel pwm method: A theoretical analysis," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 497-505, 1992.

Generalization of the pulsewidth modulation (PWM) subharmonic method to control single-phase or three-phase multilevel voltage source inverters (VSI) is considered. An analytical expression of the spectral components of the output waveforms covering all the operating conditions is derived. The analysis is based on an extension of Bennet's method. The improvements in harmonic spectrum are pointed out, and several examples are presented, which prove the validity of the multilevel modulation.

[380] K. W. Marschke, P. P. A. Caldeira, and T. A. Lipo, "Utilization of the series resonant dc link converter as a conditioning system for smes," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 506-513, 1992.

A superconductive magnetic energy storage (SMES) system utilizing a high-frequency series resonant DC link power converter of high efficiency as the conditioning converter is presented. This system generates a high-frequency (20 kHz or more) resonant current in a series link and switching is done at zero-current instants, reducing switching losses to a minimal value. Through the utilization of an adequate control strategy, the input power factor can be fully adjusted during the charging, storing, and discharging modes of the SMES, improving the overall system efficiency. Different semiconductor devices are used as the switching losses are established for each case. Experimental results from a monophase and three-phase system verified the results obtained from digital simulation.

[381] L. Hu and R. Yacamini, "Harmonic transfer through converters and hvdc links," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 514-525, 1992.

Power converters are known to be generators of harmonics on both their AC and DC sides. They also transfer existing harmonics from one side to the other side with an associated change of frequency. Analysis techniques that can be used to calculate these transferred harmonics using amplitude modulation (AM) theory are proposed. The authors also show how, in a high-voltage direct-current (HVDC) link, the converters can intercouple the AC and DC systems and can thus act as a transfer medium for harmonics. Examples that show how to calculate these harmonics are given and comparisons are made with a computer-aided design (CAD) model as a check on the accuracy of the method.

[382] M. D. Bellar, E. H. Watanabe, and A. C. Mesquita, "Analysis of the dynamic and steady-state performance of cockcroft-walton cascade rectifiers," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 526-534, 1992.

The analysis of Cockcroft-Walton cascade rectifiers for static and dynamic conditions, based on digital simulations, is presented. Steady-state and transient currents and voltages on any component can be calculated through simulation. The influence of the voltage source impedance (generally inductive), in the overall performance, is shown to be very important. Experimental results are presented to validate the analysis.

[383] Y.-S. Lee, D. K. W. Cheng, and S. C. Wong, "A new approach to the modeling of converters for spice simulation," IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 741-753, 1992.

An approach to the modeling of DC-DC converters for SPICE simulation is developed in which the average current in the energy-storage inductor is first simulated in a SPICE subcircuit for both the continuous and discontinuous modes of operation. The inductor current is then weighted and redistributed to related branches of the circuit to simulate the average input and output currents of the converter. Based on this technique, various converter models, including that of the Cuk converter with coupled inductors, which are valid for both continuous and discontinuous modes of operation, are developed.

[384] R. H. Brown and M. Jaroudi, "Torque prediction and maximization strategies for bifilar-wound hybrid step motors," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 535-541, 1992.

A method to predict torque-speed characteristics of the bifilar-wound hybrid step motor with the inverse-diode-clamped drive circuit is presented. The phase excitation control strategies that maximize and minimize average torque production are found. A closed-form expression for average torque produced by the motor is found by representing the flux linkages and model parameters as Fourier series. The predicted average torque function is compared to other methods and experimentally measured results. Inclusion of the drive circuit model is shown to significantly improved prediction of torque speed characteristics.

[385] S.-i. Furuya, T. Maruhashi, Y. Izuno, and M. Nakaoka, "Load-adaptive frequency tracking control implementation of two-phase resonant inverter for ultrasonic motor," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 542-550, 1992.

The operating principles of newly developed ultrasonic motors (USMs) that are attractive as compact and high-torque actuators are described. A two-phase high-frequency resonant inverter for driving the USM is presented. The unique operating characteristics of the USM are examined using the inverter. Two principles of resonant frequency tracking control strategy, one concerned with a sensor interface scheme mounted on the USM and a second sensorless interface scheme based on electromechanical conversion theory, are described. These control methods are realized by analog-oriented signal processing and the PLL technique. The revolving speed control obtained by this inverter-fed USM system with two types of resonant frequency tracking control methods is illustrated and discussed using an experimental breadboard.

[386] L. Ben-Brahim and A. Kawamura, "Digital control of induction motor current with deadbeat response using predictive state observer," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 551-559, 1992.

For a high-power induction motor drive, the switching frequency of the inverter cannot become higher than one kilohertz, and such a switching frequency produces a large current ripple, which then produces torque ripple. To minimize the current ripple, a method based on deadbeat control theory for current regulation is proposed. The pulsewidth modulation (PWM) pattern is determined at every sampling instant based on stator current measurements, motor speed, current references, and rotor flux vector, which is predicted by a state observer with variable poles selection, so that the stator currents are controlled to be exactly equal to the reference currents at every sampling instant. The proposed method consists of two parts: (1) derivation of a deadbeat control and (2) construction of a state observer that predicts the rotor flux and the stator currents in the next sampling instant. This paper describes a theoretical analysis, computer simulations and experimental results.

[387] Y. Baudon, D. Jouve, and J.-P. Ferrieux, "Current control of permanent magnet synchronous machines. Experimental and simulation study," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 560-567, 1992.

The control structure of a PWM (pulsewidth modulation) inverter-fed sinusoidal synchronous motor commonly includes two or three current control loops. Previous simulation studies have shown that the three-loop structure should be preferred: hence the neutral-point voltage can move freely. To obtain the same results with the two-loop structure, a more complex control variable limitation strategy is compulsory. However, the three-loop structure is very sensitive to imperfections in the control system (gain errors and offsets). Simulation and experimental results for both structures are compared and the influence of a neutral-point voltage (NPV) feedback loop to cancel homopolar errors in the three-loop structure is discussed.

[388] M.-a. Fukase, T. Nakamura, and J.-i. Nishizawa, "A circuit simulator of the sith," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 581-591, 1992.

A classification of circuit simulators is provided and the techniques used in these simulators to cater to requirements for the static induction thyristor (SITh) are examined. A circuit simulator expressly for the SITh is reported. Circuit equations implicitly containing two-dimensional (2-D) physical device equations are computed by the Newton-Raphson method. The incompletely rectangular mesh structure of M. S. Adler (1978) is modified to conveniently handle current equations at an arbitrary state. Terminal currents are precisely computed by counting displacement currents that have not been simulated but are experimentally known to be important. The model includes the crystal orientation of the wafer. The simulation makes clear how to design gate doping and control the gate during on-states to improve forward voltage drop without violating forward-blocking capability. Simulation of the turn-off state proves the reliability of the circuit simulator physically as well as mathematically.

[389] K. D. T. Ngo, R. P. Alley, A. J. Yerman, R. J. Charles, and M. H. Kuo, "Design issues for the transformer in a low-voltage power supply with high efficiency and high power density," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 592-600, 1992.

Circuit model, design feasibility, and design tradeoffs are investigated for the transformer in 1.5-5-V power supplies with high efficiency and high power density. The transformer is constructed from a single or a matrix of pot cores and from interleaved planar windings. It has been determined theoretically and verified experimentally that such a transformer is realizable as long as the loss constraint is not severe (e.g., less than 0.5 W transformer loss per 100 W output). The primary source of loss is the winding, not the core, in 1.5 V/turn design. Measures to reduce the transformer height tend to increase transformer loss or volume.

[390] K. D. T. Ngo and R.-S. Lai, "Effect of height on power density in spiral-wound power-pot-core transformers," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 601-606, 1992.

The effect of height on power density in spiral-wound power-pot-core transformers is examined for the practical range of power, frequency, loss, and volt-per-turn. Relevant mechanical and electrical equations are derived and applied to an optimization algorithm that searches for the design that maximizes the power density at a given height. It has been found that the curves of power density versus height exhibit a peak (on the order of 1000 W/in³ in several cases) at a critical height between 0.25 and 0.3 in. Below this critical height, the power density decreases drastically.

[391] M. A. Morrill, V. A. Caliskan, and C. Q. Lee, "High-frequency planar power transformers," IEEE Transactions on Power Electronics, vol. 7, no. 3, pp. 607-613, 1992.

High-frequency transformer design using the transmission line transformer (TLT) is described. Utilizing transmission line circuit theory, the characteristics of the TLT for different turn ratios are given, and its advantages, including its wideband nature, are discussed. TLT prototypes with turn ratios of 2:1, 3:1, and 5:1 were designed and fabricated. The prototype test results verify the theoretical analysis and also point out the further advantage of compact size, making the TLT approach a promising transformer design alternative for use in high-frequency converters.

[392] M. Ehsani, O. H. Stielau, J. D. van Wyk, and I. J. Pitel, "Integrated reactive components in power electronic circuits," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 208-215, 1993.

Methods of integrating capacitive and inductive components into new compact devices are presented. Configurations for integrating various combinations of L-C networks are shown. A practical example of constructing an integrated L-C for a series resonant converter is evaluated both practically and experimentally.

[393] C. Jamerson and D. Y. Chen, "Techniques for reduction of required headroom in high-frequency magamp postregulators," IEEE Transactions on Power Electronics, vol. 8, no. 1, pp. 90-94, 1993.

High headroom in a magamp postregulator increases circuit losses, including power transistor losses, saturable reactor core loss, and freewheeling diode snubber loss. Higher headroom also requires the use of higher voltage diodes. This paper describes common causes for large headroom requirement and discusses various techniques to reduce it.

[394] S. Ohtsu, T. Yamashita, K. Yamamoto, and T. Sugiura, "Stability in high-output-voltage push-pull current-fed converters," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 135-139, 1993.

This paper studies the relationship between the magnetizing inductances of a transformer and of a choke coil in high-voltage power supplies. This analysis defines the conditions for high switching frequency and stable operation of high-voltage power supplies without the power loss increase. This approach is confirmed by the implementation of a high-voltage power supply operating at 200 kHz with a high efficiency of 86%.

[395] R. M. Duke and S. D. Round, "Steady-state performance of a controlled current active filter," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 140-146, 1993.

An active filter that uses a high-frequency D-class asynchronous switching inverter for power system current distortion compensation is described. The distortion compensation technique involves deriving a signal corresponding to the distortion component of load current, and inverting and amplifying this signal for addition back to the supply current to cancel the load current distortion. A synthetic sinusoid is used to determine the distortion component in the time domain. Extensive computed and experimental results, illustrating the system's steady-state performance and ability to reduce the current harmonic distortion components, are presented. An intelligent controller is proposed to maintain the active filter's performance at the optimal operating point under varying load conditions.

[396] L. Malesani and R. Piovan, "Theoretical performance of the capacitor-diode voltage multiplier fed by a current source," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 147-155, 1993.

In this paper, theoretical performance of the CDVM is studied, with impressed current input and constant voltage output. The operating modes of the CDVM are described, and the expressions of the voltages and currents are derived for the incomplete configuration. The results are immediately extended to any input waveform. The case of sinusoidal current input is fully characterized, giving useful design expressions.

[397] S. Bhowmik and R. Spee, "Guide to the application-oriented selection of ac/ac converter topologies," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 156-163, 1993.

Recent developments in power semiconductor and converter technologies have led to a proliferation of circuit topologies with sometimes contradictory performance claims. For the nonspecialist application engineer, this can often lead to uncertainty, which potentially results in nonoptimum converter selections. This paper presents a comprehensive review and a comparative evaluation of ac/ac converter topologies. This provides guidelines for selecting an optimum technology for a given application. While review and evaluation are done at a relatively high level, the comprehensive literature section provides access to design details.

[398] R. Liu, I. Batarseh, and C. Q. Lee, "Comparison of capacitively and inductively coupled parallel resonant converters," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 445-454, 1993.

Both the capacitively and inductively coupled parallel resonant converters are analyzed by means of the state-plane technique. Based on the results of the analysis, we present a set of characteristic curves for the converters operated in the continuous conduction mode. These curves can be used to facilitate the analysis and design for such converters. Comparison of circuit performances between these converters is discussed. A detailed design example for both converters is presented.

[399] C. M. Liaw and S. J. Chiang, "Robust control of multimodule current-mode controlled converters," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 455-465, 1993.

A robust controller for multimodule current-mode push-pull converters is presented. First, the small-signal equivalent circuit and transfer function model of the multimodule converter system are found. Then the selection of slope compensation and the model reduction are performed using the concept of dominant energy mode. Based on the reduced converter model, a PI controller is quantitatively designed according to the prescribed regulating specifications using a systematic design procedure. A robust controller is proposed and augmented to improve the control performance when the parameter variations caused by system configuration change and operating point shift have occurred. The performance of the converter and the effectiveness of the proposed controller are demonstrated by some simulated and experimental results.

[400] B. Choi, B. H. Cho, F. C. Lee, and R. B. Ridley, "Three-loop control for multimodule converter systems," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 466-474, 1993.

A three-loop control scheme for multimodule converter systems with a secondary LC filter is presented. In addition to output voltage and inductor current feedback, the control scheme employs feedback from the output capacitor of each module to improve the dynamic performance of the system, particularly the transient response in the event of failure of a module. The superiority of the three-loop control over the conventional two-loop current mode control is demonstrated by both small-signal analysis and large-signal simulations.

[401] G. Hua, F. C. Lee, and M. M. Jovanovic, "Improved full-bridge zero-voltage-switched pwm converter using a saturable inductor," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 530-534, 1993.

The saturable inductor is employed in the full-bridge (FB) zero-voltage-switched (ZVS) pulsewidth-modulated (PWM) converter to improve its performance. The current and voltage stresses of the switches as well as parasitic oscillations are significantly reduced compared to those of the conventional FB-ZVS-PWM converter. The qualitative analysis is presented and is verified on a 500 KHz, 5 V/40 A converter.

[402] B.-T. Ooi and S.-Z. Dai, "Series-type solid-state static var compensator," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 164-169, 1993.

A fast response, electronically controlled, continuously variable equivalent capacitive reactance for series compensation of utility transmission lines is described. Unlike compensation by series dielectric capacitors, there is no fear of subsynchronous resonance (SSR) instability. A high level of compensation is possible because there is no danger of forced resonance by the supply frequency. Experimental and digital simulation results are presented.

[403] F. Swift and A. Kamberis, "New walsh domain technique of harmonic elimination and voltage control in pulse-width modulated inverters," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 170-185, 1993.

A new method is presented for selective harmonic elimination in pulse-width modulated (PWM) inverter waveforms by the novel use of Walsh functions. The Walsh operational matrix of pulse-width modulation (WOM-PWM) is introduced as a means of obtaining the Walsh spectral equations of PWM waveforms. The slope and intercept Fourier operational matrices of pulse-width modulation (SFOM-PWM and IFOM-PWM) are also introduced as a means of obtaining Fourier spectral equations of PWM waveforms. A noniterative algorithm is proposed that produces piecewise linear, global solutions between angles and voltage fundamental, without the need of initial starting values for the angles. The algorithm also produces the full range of variation of fundamental voltage for given harmonic elimination constraints. The set of systems of linear equations obtained replaces the system of nonlinear transcendental equations used in the Fourier series harmonic elimination approach. In general, the algorithm makes possible the synthesis of two-state PWM inverter waveforms with specified odd harmonic content.

[404] K. Matsui, Y. Murai, M. Watanabe, M. Kaneko, and F. Ueda, "Pulsewidth-modulated inverter with parallel connected transistors using current-sharing reactors," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 186-191, 1993.

A technique of parallel connection of transistors by using current-sharing reactors for the pulsewidth modulated (PWM) transistor inverter is reported in this paper. The proposed technique not only increases the current capacity to handle but also decreases the output harmonic contents. The output voltage waveforms of the proposed inverter have certain voltage levels during their half cycles, thus it is anticipated that it will be difficult to analyze the output harmonics. For such waveforms, frequency analysis approach is described, whose results are verified by experiments.

[405] I. D. Hassan, R. M. Bucci, and K. T. Swe, "400 mw smes power conditioning system development and simulation," IEEE Transactions on Power Electronics, vol. 8, no. 3, pp. 237-249, 1993.

A conceptual design for a 22 MWh superconducting magnetic energy storage (SMES) system engineering test model (ETM) has recently been developed. The objectives of the SMES-ETM are to demonstrate the feasibility of using a SMES system to perform load-leveling and system stabilization for commercial utilities and to supply 400 MW power pulses for ground-based defense systems. This paper presents the performance requirements and configuration of the proposed 22 MWh SMES-ETM and its power conditioning system. The power conditioning system consists of a dc-dc chopper linked to a GTO-based voltage source converter interfacing the superconducting energy storage coil to the ac power system. The SMES system operation in the charging and discharging modes is described and the results of digital simulations demonstrating the feasibility of the proposed power conditioning system and exploring its overall behavior under normal and fault conditions are presented.

[406] Z.-C. Zhang and B.-T. Ooi, "Multimodular current-source spwm converters for superconducting a magnetic energy storage system," IEEE Transactions on Power Electronics, vol. 8, no. 3, pp. 250-256, 1993.

This paper points to the advantages of using multiple modules of the current-source, SPWM, three-phase six-valve converters as the power conditioner for the superconducting magnetic energy system. A high degree of controllability is obtained by using dynamic SPWM trilogic as the operating strategy. Very low switching losses is assured by using two carrier triangles per modulating cycle. By parallel connection of converter modules, and by phase-shifting the triangle carriers, the following are the gains: 1) increasing the current capacity to the level required by the superconducting magnetic, 2) reduction of conduction losses, 3) meeting harmonic standards, without the need of expensive filter, by harmonic cancellation, and 4) achieving a high-frequency bandwidth.

[407] R. C. Thurston and S. F. Legowski, "Simple and accurate method of computing average and rms currents in a three-phase pwm inverter," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 192-199, 1993.

The design of three-phase PWM inverters requires values for the average and rms currents in the inverter in order to select the right components. A computer-aided investigation of approximate inverter current waveforms indicates that the average and rms inverter currents are simple functions of a single factor equal to the product of the power factor and the modulation index. These functions have been expressed as per-unit equations that are useful not only for designing new inverters, but also for evaluating existing designs.

[408] K. D. T. Ngo, E. Alpizar, and J. K. Watson, "Modeling of magnetizing inductance and leakage inductance in a matrix transformer," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 200-207, 1993.

Winding and core geometries are described for a matrix transformer constructed from integrated core and z-folded flex circuits. The magnetizing inductance is derived using reluctance method and exploiting structural periodicity and symmetry. The internal leakage inductance is computed from magnetic field distribution and the interconnect leakage inductance from inductance formulas and current distribution. The results show that the interconnects are responsible for most of the leakage inductance. The modeling approaches predict inductance values that agree well with experimental measurements.

[409] M. Ehsani, I. Husain, and M. O. Bilgic, "Inverse dual converter (idc) for high-power dc-dc applications," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 216-223, 1993.

A new family of dc-dc converters, suitable for high-power dc-dc conversion, is presented. The inverse dual converter (IDC) is capable of continuous voltage step-up or step-down control over a wide range and without the need of a transformer.

[410] M. Ehsani, I. Husain, K. R. Ramani, and J. H. Galloway, "Dual-decay converter for switched reluctance motor drives in low-voltage applications," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 224-230, 1993.

A modified converter topology for star-connected switched reluctance motors suitable for low-voltage applications is proposed in this paper. A dual time constant freewheeling circuit has been designed to improve the drive performance and efficiency over a wide range of speeds. The different modes of operation of the converter are discussed, and a comparison is made with other converter configurations.

[411] C.-S. Berendsen, G. Champenois, and A. Bolopion, "Commutation strategies for brushless dc motors: Influence on instant torque," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 231-236, 1993.

This paper presents a solution to obtain torque smoothness of a brushless dc drive within a wide speed range. The voltage between the neutral point N₀ of the inverter and the neutral point N of the machine (V_NN(0) voltage) is not always zero. This voltage disturbs the phase currents during commutation. Since, in the case of real EMF's, the limited loop bandwidth of the current controller does not allow the currents to follow the adapted reference, a compensative and a predictive term have been added to the controller output. Furthermore, the robustness of the concept in the case of parameter variations is studied.

[412] R. Tymerski and D. Li, "State-space models for current programmed pulsewidth-modulated converters," IEEE Transactions on Power Electronics, vol. 8, no. 3, pp. 271-278, 1993.

State-space models are derived for pulsewidth-modulated (PWM) converters operating at constant switching frequency under current programmed control. One model neglects the sample-and-hold effect of the current loop and is therefore representative of the traditional approach taken to modeling current programmed converters. The order of the model is the same as that of the power stage. A second state-space model is derived which incorporates the sample-and-hold effect. The order of this model is two higher than that of the power stage. A comparison of the two models is made which clearly demonstrates the superiority of the second modeling approach. As the models are in state-space form they may be quite readily used in a CAD package for general converter analysis and design, to determine all transfer functions and associated pole/zero locations of interest.

[413] P. P. Acarnley, "Observability criteria for winding currents in three-phase brushless dc drives," IEEE Transactions on Power Electronics, vol. 8, no. 3, pp. 264-270, 1993.

A rigorous method of applying observability criteria to the estimation of winding currents in brushless dc drives is presented. Observability is related to both the drive's operating condition, both motoring and regenerating, and to the PWM switching strategy being employed. The precise conditions under which motor winding currents can be estimated from measurements of dc link current are clearly defined. A modified single current sensor arrangement, in which switching device currents are measured, is shown to improve the observability of currents with complementary switching, but to have an adverse effect on observability with the basic switching strategy. An arrangement involving two current sensors allows discontinuous estimation of the winding currents for all operating conditions and both switching strategies. The primary advantage of this technique is that measurements by each sensor are made equally on all three phases of the motor.

[414] G. Venkataramanan, D. M. Divan, and T. M. Jahns, "Discrete pulse modulation strategies for high-frequency inverter systems," IEEE Transactions on Power Electronics, vol. 8, no. 3, pp. 279-287, 1993.

High-performance high-frequency inverter systems for UPS applications represent a demanding application that cannot be easily realized using conventional hard-switched PWM inverter topologies. Adoption of typical soft-switched inverters such as the resonant dc link inverter require the use of discrete pulse modulation strategies. New controller structures are necessary to cope with stringent voltage regulation and distortion constraints in the presence of unbalanced and nonlinear loads. This paper presents a controller that utilizes load current feed-forward strategy with a cost function current regulator to achieve excellent transient performance characteristics. Voltage regulation is ensured using a synchronous frame regulator. Detailed simulation and experimental results verifying the concepts are presented. Although this paper focuses on soft-switching inverters, the control concepts can be applied to conventional hard-switching inverters as well.

[415] E. S. Lee and T. G. Wilson, Jr., "Electrical design inspection: A methodology for using circuit simulation in the design and development of electronic power supplies," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 475-485, 1993.

A statistical analysis of AT&T's electronic power supply design process indicates that as many as 50% of electrical design faults that are discovered during the product realization process could be detected by an appropriately structured circuit simulation. Early detection of circuit design flaws allows errors to be corrected before the development team commits to a prototyping cycle, thus eliminating wasteful design iterations. Prior to the development of advanced circuit simulation techniques, the state of circuit simulation tools was not yet to the point where production schematics of switching power supplies could be simulated as a regular design practice. In this paper, we present an electrical design inspection methodology that combines advanced power circuit simulation techniques and RISC (Reduced Instruction Set Computing) workstation hardware to use simulation in the day-to-day design of electronic power supplies. This methodology is embedded in an electrical design inspection system, designed to detect one class of design mistakes and prevent them from propagating further in the product realization process. We describe the methodology and the implementation of the inspection system. Preliminary results of the application of this methodology to our electronic power supply products are also presented. Finally, we discuss future enhancements to the methodology and how this methodology can benefit the product realization process.

[416] J. R. Pinheiro and I. Barbi, "Three-level zvs-pwm dc-to-dc converter," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 486-492, 1993.

A new high frequency dc-to-dc power converter for high voltage and high power is introduced in this paper, which features zero-voltage-switching, operation at constant frequency, regulation by pulsewidth modulation, and low rms current stress upon power switches. Its greatest attribute, in comparison with the full-bridge (FB-ZVS-PWM) converter, is that the voltage across the switches is half of the input voltage. This property is achieved due to the employment of a three-level leg in place of the conventional two-switch leg. Operation, analysis, design procedure and example, and simulation are presented. A prototype operating at 100 kHz, rated at 600 V input voltage, and 1.5 kW output power and 25 A output current has been fabricated and successfully tested in the laboratory.

[417] A. Maheshwari and K. D. T. Ngo, "Synthesis of six-step pulsewidth-modulated waveforms with selective harmonic elimination," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 554-561, 1993.

By selectively eliminating several lower-order harmonics, programmed pulsewidth modulation (PWM) techniques generate high-quality output spectra. This paper presents a new technique of selective harmonic elimination (S.H.E.) for synthesizing line-to-line voltages in single-phase and three-phase inverters. The technique eliminates all triplen and even harmonics, utilizes up to 100% of the dc bus voltage, and guarantees that the three-phase voltages sum up to zero at any instant.

[418] P. N. Enjeti and S. A. Choudhury, "New control strategy to improve the performance of a pwm ac to dc converter under unbalanced operating conditions," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 493-500, 1993.

Abnormal harmonics of significant magnitude are generated at the output and input terminals of a PWM ac to dc converter under unbalanced operating conditions. A new control strategy is presented here to selectively cancel the generated lower order abnormal harmonics at the output and input terminals and thereby to preserve the high performance features of a PWM ac to dc converter. The proposed technique essentially involves computing the sequence components of the unbalanced input supply and suitably counter-unbalances the PWM gating signals of the converter switches to cancel the generated abnormal harmonics. The technique is essentially a feed forward approach and is suitable for higher power G.T.O. type PWM ac to dc converters. A procedure for implementing this technique in real time is discussed. Finally selected results are verified experimentally on a prototype PWM ac to dc converter.

[419] C.-T. Pan and T.-C. Chen, "Modeling and design of an ac to dc converter," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 501-508, 1993.

In this paper, a step-up/down single-phase ac-to-dc converter without current sensor is proposed to achieve high performance and simple control logic. The converter adopts a front-end diode rectifier so that only one active switch is required. The familiar state-space averaging technique for discontinuous mode dc to dc converters is extended to model the proposed ac to dc converter. Unlike the existing model, which is valid only for very low frequency range, namely below line frequency, the proposed model is applicable up to half switching frequency. Design of the controller is detailed for reference. Finally, some selected experimental results are presented to verify the proposed theory.

[420] J. C. Salmon, "Techniques for minimizing the input current distortion of current-controlled single-phase boost rectifiers," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 509-520, 1993.

This paper describes techniques for minimizing the input current distortion of current-controlled single-phase boost rectifiers. The switching patterns of several boost rectifiers are examined to identify the nature of their input current waveforms. This analysis is then used to examine the low-frequency current distortion levels, and hence power quality, associated with the rectifiers. A PWM strategy that selectively switches between positive unipolar PWM and negative unipolar PWM, called `phase-adjusted unipolar PWM,' is shown to produce the lowest current distortion levels. A new 2-switch asymmetrical half-bridge rectifier is presented that draws an input current at a unity fundamental power factor and with the same low distortion as obtained with the 4-switch H-bridge rectifier. The operation of the various rectifiers is examined with reference to theoretical predictions, circuit simulations, and experimental results. This analysis, using a per-unit system based upon the magnitude of the rectifier inductor, is then used to compare the performance of the various rectifier switching patterns.

[421] J. C. Salmon, "Circuit topologies for single-phase voltage-doubler boost rectifiers," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 521-529, 1993.

A new family of single-phase voltage-doubler PWM boost rectifiers is presented in this paper. By examining the switching states of several `standard' single-phase boost rectifier circuits, three characteristic PWM voltage switching patterns are identified: unipolar PWM; bipolar PWM and phase-adjusted unipolar PWM. From this analysis, an equivalent family of voltage-doubler rectifiers is derived. When high output voltages are required, voltage-doubler rectifiers are shown to be able to generate ac-line currents with the lowest current distortion. All circuits presented in this paper are examined using circuit simulators and experimental results.

[422] A. K. S. Bhat, "Analysis and design of a series-parallel resonant converter," IEEE Transactions on Power Electronics, vol. 8, no. 1, pp. 1-11, 1993.

A high-frequency link series-parallel resonant converter is analyzed using the state-space approach. Analysis is presented for both the continuous capacitor voltage mode and the discontinuous capacitor voltage mode. Steady-state solutions are derived. Design curves for the converter gain and other component stresses are obtained. A method of optimizing the converter under certain constraints is presented and a simple design procedure is illustrated by a design example. Experimental results are presented to verify the theory.

[423] X. Wang and B.-T. Ooi, "Unity pf current-source rectifier based on dynamic trilogic pwm," IEEE Transactions on Power Electronics, vol. 8, no. 3, pp. 288-294, 1993.

One remaining step in perfecting the stand-alone, unity power factor, regulated current-source PWM rectifier is to reduce cost, by bringing the 12-valve converter (consisting of three single-phase full bridges that operate with two-level or bilogic PWM) to the six-valve bridge. However, the six-valve topology requires a three-level or trilogic PWM strategy that can handle feedback signals. This feature was not available until now. The paper describes a general method of translating three-phase bilogic PWM signals to three-phase trilogic PWM signals. The method of translation retains the characteristics of the bilogic PWM, including the frequency bandwidth. Experiments show that the trilogic PWM signals produced by the method can not only handle stabilizing feedback signals but also signals for active filtering.

[424] X. Wang and B.-T. Ooi, "Real-time multi-dsp control of three-phase current-source unity power factor pwm rectifier," IEEE Transactions on Power Electronics, vol. 8, no. 3, pp. 295-300, 1993.

The design of a real-time multi-DSP controller for a high-quality six-valve three-phase current-source unity power factor PWM rectifier is discussed in this paper. With the decoupler preprocessor and the dynamic trilogic PWM trigger scheme, each of the three input currents can be controlled independently. Based on the a-b-c frame system model and the fast parallel computer control, the pole-placement control method is implemented successfully to achieve fast response in the ac currents. The low-frequency resonance in the ac filter L-C networks has been damped effectively. The experimental results are obtained from a 1-kVA bipolar transistor current-source PWM rectifier with a real-time controller using three TMS320C25 DSP's.

[425] G. L. van Harmelen and J. H. R. Enslin, "Real-time dynamic control of dynamic power filters in supplies with high contamination," IEEE Transactions on Power Electronics, vol. 8, no. 3, pp. 301-308, 1993.

A real-time closed-loop controller system used for controlling dynamic power filters under rapidly varying nonlinear loading conditions, is tested and evaluated. With the aid of a dedicated microprocessor system, using correlation algorithms, real-time reference signals for a dynamic compensation system are generated. In order to facilitate a cost effective compensation system, separate compensation of the fundamental reactive power component and the harmonic components is further investigated. A total algorithm time of 312 μs in a 50 Hz system is achieved, providing accurate compensation effort up to the 21st power system harmonic.

[426] R. Farrington, M. M. Jovanovic, and F. C. Lee, "New family of isolated converters that uses the magnetizing inductance of the transformer to achieve zero-voltage switching," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 535-545, 1993.

A new family of isolated, zero-voltage-switched converters which utilizes the magnetizing inductance of the transformer to achieve zero voltage turn-on of the primary switches is proposed. By employing saturable inductor(s) on the secondary side, soft turn-off of the output rectifier(s) is obtained with a minimum circulating energy flowing through the converter. The proposed converters can operate either with a variable or constant switching frequency. A complete dc analysis and design guidelines for the half-bridge topology are described, and the performance of a 100 W experimental converter is presented.

[427] J. Holtz, W. Lotzkat, and A. M. Khambadkone, "On continuous control of pwm inverters in the overmodulation range including the six-step mode," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 546-552, 1993.

The power output and the dynamic performance of PWM controlled ac drives can be improved by increasing the inverter output voltage through overmodulation. Two different solutions are proposed to increase the output voltage in a continuously controllable fashion up to the maximum possible value, which is reached in the six-step mode. The solutions differ in their respective approach. A space vector strategy is used for high-dynamic performance high-switching frequency drives, while a field-oriented PWM method applies for low switching frequency high-power inverters. The methods are described and analyzed and the experimental results are presented.

[428] S. J. Finney, T. C. Green, and B. W. Williams, "Spectral characteristics of resonant-link inverters," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 562-570, 1993.

Improvement in the frequency spectrum of resonant-link inverters does not match the increase in switching frequency because of the restriction of integral pulse modulation schemes such as delta modulation. Comparisons of low-frequency pulse width modulation with high-frequency delta modulation show that the spread spectrum of delta modulation may cause problems owing to low-frequency harmonics, despite a better total harmonic distortion. An assessment of total losses, for a bipolar junction transistor Darlington example, is used to set the operating frequency in each modulation case.

[429] M. Mikolajewski and M. K. Kazimierczuk, "Zero-voltage-ripple rectifiers and dc/dc resonant converters," IEEE Transactions on Power Electronics, vol. 8, no. 1, pp. 12-17, 1993.

Class E zero-voltage-ripple (ZVR) rectifiers are introduced. The proposed circuits offer a new means of a significant improvement in suppressing the output-voltage ripple compared with their predecessors. Therefore, the size of the output filter can be considerably reduced, the r I_rms² conduction power loss in the ESR of the filter capacitor can be lowered, aluminum or tantalum electrolytic capacitors may be entirely eliminated, filter capacitors with low capacitances and thereby high self-resonant frequencies can be used, and a faster dynamic response becomes achievable. Zero-voltage ripple is accomplished by reducing the ac component of the current at the input of the output filter. Using the Class E ZVR rectifiers, Class E² and Class D-E ZVR resonant dc/dc converters are derived. An experimental prototype of a Class E² 30 W/500 kHz dc/dc converter was built and tested. Its output-voltage ripple was as much as 20 times lower than that of the corresponding conventional converter. The new converters are suitable for noise-sensitive high-output-current applications.

[430] K. Chen and T. A. Stuart, "1.6-kw, 110-khz dc-dc converter optimized for igbt's," IEEE Transactions on Power Electronics, vol. 8, no. 1, pp. 18-25, 1993.

A full bridge dc-dc converter using a zero-current and zero-voltage switching technique is described. This circuit utilizes the characteristics of the IGBT to achieve power and frequency combinations that are much higher than previously reported for this device. Experimental results are included for a 1.6-kW, 110-kHz converter with 95% efficiency.

[431] C. Jamerson and D. Y. Chen, "Magamp postregulators for symmetrical topologies with emphasis on half-bridge configuration," IEEE Transactions on Power Electronics, vol. 8, no. 1, pp. 26-29, 1993.

This paper points out the major differences between symmetrical topology magamps and the forward converter magamp. In a forward converter, a small portion of the magnetizing current of the power transformer is diverted to the secondary for reset of the magamp's saturable reactor. In symmetrical topologies, the transformer's magnetizing current is not used for reset of the saturable reactor(s). The magnetizing current shifts to the secondary where it causes a series of problems. This paper examines these problems, identifies solutions, and explains why a half-bridge magamp supply is inherently less versatile than is the forward converters.

[432] T. G. Habetler, "Space vector-based rectifier regulator for ac/dc/ac converters," IEEE Transactions on Power Electronics, vol. 8, no. 1, pp. 30-36, 1993.

A voltage-sourced rectifier control scheme for use with ac/dc/ac variable speed drives is presented in this paper. A control scheme is derived that directly calculates the duration of time spent on the zero state and on each switching state adjacent to the reference vector, over a constant switching interval, in order to drive the line current vector to the reference vector. In addition, under transient conditions, when deadbeat control is not possible, a control scheme is presented that ensures that the line current vector is driven in the direction of the reference current vector. The current reference for the rectifier controller is derived from the bus voltage error and a feedforward term based on the estimated converter output power. The proposed space vector-based rectifier regulator is shown to exhibit improved harmonic and transient performance over existing per-phase duty cycle prediction methods, especially at modulation indices near unity. The deadbeat control of the rectifier input current is accomplished every half-cycle with constant switching frequency while still symmetrically distributing the zero state within the half-cycle period. In this way, satisfactory performance under various operating conditions is achieved with relatively low switching frequencies and high bus voltage ripple.

[433] C.-C. Liu, J. Hsieh, C. H. K. Chang, J. M. Bocek, and Y.-T. Hsiao, "Fast-decoupled method for time-domain simulation of power converters," IEEE Transactions on Power Electronics, vol. 8, no. 1, pp. 37-45, 1993.

This study is concerned with fast long-term dynamic simulation of power converters. Because of switching actions, the converter can operate in different configurations and, therefore, it can be represented by a state-space time-varying linear system. This paper presents a new method for calculating switching time from an accurate and explicit form of the switching condition, hence the step-by-step search of the switching instant can be greatly simplified. In the proposed algorithm, a converter is partitioned into subsystems, which are simulated in a decoupled manner and coordinated through data exchange.

[434] M. Mirkazemi-Moud, T. C. Green, and B. W. Williams, "Analysis and comparison of real-time sine-wave generation for pwm circuits," IEEE Transactions on Power Electronics, vol. 8, no. 1, pp. 46-54, 1993.

The paper presents four methods for hardware and software generation in real time of sine waves suitable for PWM circuits. The sine waves are derived from a truncated modified cosine Taylor series, wt(φ-wt) function, a digitally filtered trapezoid, and a second-order differential equation. Triplen injection is incorporated by the addition of a defined magnitude triangular waveform of three times the fundamental frequency. Each sine-wave generating technique is implemented, as applicable, in a programmable logic cell array and/or in microprocessor-based software. In each case, the output spectra and total harmonic distortion are compared with computer-simulated results.

[435] G. Joos, G. Moschopoulos, and P. D. Ziogas, "High performance current source inverter," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 571-579, 1993.

A recent innovation in current source inverter (CSI) drives has been the introduction of pulsewidth modulation (PWM) for the purpose of improving the quality of the load currents and voltages. However, the typical six switch CSI circuit is not compatible with all standard PWM techniques thus limiting the number of schemes that can be used. The modified CSI circuit discussed in this paper removes most of the restrictions at the `cost' of an extra switch. Additional advantages include faster response times through modulation index control and higher efficiency. This paper includes a detailed steady-state analysis and design procedure. The feasibility and performance of the modified CSI are verified by simulation and experimental implementation on a 5 kVA converter.

[436] S.-C. Wong and Y.-S. Lee, "Spice modeling and simulation of hysteretic current-controlled c uk converter," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 580-584, 1993.

Based on some new techniques which we have proposed for the modeling of PWM-controlled converters, the low-frequency behavior models of hysteretic current-mode controlled C uk converters, including the ones with coupled inductors, are developed. These models are simple, accurate and easy to use. Computer simulations based on such models are carried out for the analysis of the partial V_o/ partial V_i and partial V_o/ partial I_C transfer characteristics and transient responses. The simulations are also verified by experimental measurements.

[437] R. Tymerski and D. Li, "Extended ripple analysis of pwm dc-to-dc converters," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 588-595, 1993.

By employing a Taylor series expansion of the state, simplified expressions are derived for the first- and second-order terms of the state ripple of any pulsewidth-modulated (PWM) dc-to-dc converter operating in continuous conduction mode. With the assumption that the ripple is dominated by its lowest order nonzero component, along with the ripple order relationships between state variables, these expressions may be used on any PWM converter to derive design guidelines for optimum ripple performance. An example is given of a fourth-order boost-type converter in which, after determining conditions by which the first two lowest-order components in the output voltage ripple are nulled, further conditions are derived that minimize the third-order component, resulting in enhanced ripple performance. The results are verified by simulation.

[438] A. C. Wang and S. R. Sanders, "Programmed pulsewidth modulated waveforms for electromagnetic interference mitigation in dc-dc converters," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 596-605, 1993.

The regular switching action of a pulsewidth modulated (PWM) circuit generates conducted and radiated electromagnetic interference (EMI), and may also generate acoustical disturbances. Programmed pulsewidth modulation techniques have been applied using various methods to control harmonics inherent in switched power circuits. In this paper, a method to generate an optimal programmed switching waveform for a dc-dc converter is presented. This switching waveform is optimized to reduce the amplitude of harmonic peaks in the EMI generated by the converter. Experimental results, a brief discussion of sensitivity, and a practical implementation of a circuit to generate the PWM waveform are given.

[439] R. Borgatti, R. Stefani, O. Bressan, F. Bicciato, P. Tenti, and L. Rossetto, "1 kw, 9 kv dc-dc converter module with time-sharing control of output voltage and input current," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 606-614, 1993.

The paper describes a dc-dc power module based on a single-stage current-fed converter structure. Control is made according to a time-sharing strategy allowing simultaneous regulation of output voltage and input current. This solution is suitable for high-performance space and avionic applications, giving high efficiency, compactness, and accuracy, speed and robustness of control. Theoretical analysis, design criteria, and experimental results are reported. Application to radar supplies is discussed.

[440] J. C. Moreira and T. A. Lipo, "New method for rotor time constant tuning in indirect field oriented control," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 626-631, 1993.

The purpose of this paper is to investigate and implement a new adaptive controller for correction of the rotor time constant used in the calculation of the slip frequency in Indirect Field Oriented Control (IFOC) of induction machines. The implementation of the controller is based on the machine air gap flux which is measured by detecting the third harmonic component of the stator phase voltages. The proposed adaptive controller depends only on a single, easily measurable machine parameter estimate, namely the magnetizing inductance. Moreover, a correction strategy to compensate for changes of the magnetizing inductance when changes in the air gap flux level occur is also proposed in this paper. Such strategy is based on a function that relates the value of this inductance to the amplitude of the third harmonic stator voltage component. This new controller does not require any sensors in the air gap of the machine nor does it require complex computations. Only access to the stator neutral connection is necessary to measure the air gap flux. Verification of the validity and feasibility of the technique is obtained from simulation and experimental results.

[441] R. C. Becerra, M. Ehsani, and T. J. E. Miller, "Commutation of sr motors," IEEE Transactions on Power Electronics, vol. 8, no. 3, pp. 257-263, 1993.

The switched reluctance motor (SRM) is currently the focus of increasing attention because of its benign operational features and its attractive control mechanisms. Its fault tolerant features make the use of the SR machine convenient in applications requiring high reliability. This paper presents commutation schemes for most common types of SR motors. These schemes permit the realization of four-quadrant multimode SR motor drive operation with simple logic control and with position feedback from low-resolution position sensors.

[442] Y.-T. Chen, D. Y. Chen, and Y.-P. Wu, "Control-loop modeling of multiple-output feedback of forward converters," IEEE Transactions on Power Electronics, vol. 8, no. 3, pp. 320-328, 1993.

A small-signal model is developed for the forward converter with multioutput feedback. From the model developed, feedback compensation schemes are proposed to stabilize the circuit. The closed-loop circuit performances, such as line regulation, cross regulation, and load regulation are expressed analytically in terms of multiple-loop gains of the system.

[443] K. D. T. Ngo, R. P. Alley, and A. J. Yerman, "Fabrication method for a winding assembly with a large number of planar layers," IEEE Transactions on Power Electronics, vol. 8, no. 1, pp. 55-61, 1993.

'Z-folding' of flex circuits is presented as a method to fabricate a winding assembly having a large number of conductive and insulating layers. Flex-circuit patterns for practical winding configurations are described along with a synthesis procedure. The steps to assemble interleaved planar windings from flex circuits are described. Equations relating winding resistance to geometrical parameters are derived for design purpose.

[444] B. H. Khan, G. K. Dubey, and S. R. Doradla, "Economical four-quadrant gto converter and its application to dc drives," IEEE Transactions on Power Electronics, vol. 8, no. 1, pp. 62-68, 1993.

This paper describes a four-quadrant converter employing a single six-GTO bridge and four thyristors as reversing switches. Such a four-quadrant converter is economical compared to a dual-converter employing two bridges, each with six GTO's. A four-quadrant dc drive employing the proposed converter and closed-loop speed control with inner current control loop is also presented. The controllers are designed using symmetric optimization. Experimental results with a 3-hp dc motor are given for steady-state and transient responses of the drive. A comparative study of the present four-quadrant drive and one reported earlier is also presented.

[445] C. Sullender, "Magnetic current sensors for space station freedom," IEEE Transactions on Power Electronics, vol. 8, no. 1, pp. 69-75, 1993.

Instrumentation on space station Freedom will require an accurate, isolated, and low-powered method of measuring high-dc currents. The magnetic current sensor presented here was created under the guidance of the NASA Lewis Research Center and is dependable, stable over time and temperature, and lightweight. Flexible topology allows the design of a pin-programmable hybrid package that contains analog and digital circuitry necessary for both bidirectional and unidirectional current sensing.

[446] P. N. Enjeti, A. Rahman, and R. Jakkli, "Economic single-phase to three-phase converter topologies for fixed and variable frequency output," IEEE Transactions on Power Electronics, vol. 8, no. 3, pp. 329-335, 1993.

In this paper, several new component minimized circuit topologies for single-phase to three-phase conversion are proposed. The proposed topologies employ fewer semiconductor devices and generate high-quality output voltages. Suitable modification to achieve active input current shaping feature is also illustrated in detail. Analysis and simulation of the proposed schemes is carried out to show the high-performance features. Suitable guides for the selection of filter components and for facilitating circuit design is presented. Finally, selected results are verified experimentally on laboratory prototype converters.

[447] S. Bertini, T. Ghiara, and M. Marchesoni, "Ac/dc/ac high voltage traction drives with quasi-zero reactive power demand," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 632-639, 1993.

The new GTO devices allow the design of forced-commuted high power converters (up to several MVA's). However, they cannot operate at high switching frequency, thus producing waveforms affected by remarkable harmonic distortion, especially if conventional converter topologies are used. A novel ac/dc/ac conversion structure has been developed referring to single-phase ac (25 kV/50 Hz) traction systems; high voltage converters delivering multilevel voltage waveforms with lower harmonic content have been employed on both the line-side and the motor-side. High performance techniques have been studied to control the whole system, assuring a quasi-unitary power factor and a low distorted line current. Simulation results confirm the validity of the methodologies proposed and of the analyses performed.

[448] V. B. Bhavaraju and P. N. Enjeti, "Analysis and design of an active power filter for balancing unbalanced loads," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 640-647, 1993.

In this paper an Active Power Filter is proposed for balancing unbalanced loads. A 3-phase, PWM ac to dc converter topology with inductive energy storage is controlled to continuously inject desired negative sequence currents into the system to achieve balancing of continuously varying unbalanced loads. The principal of operation is as follows: the negative sequence components of the load currents are measured in magnitude and in phase and the PWM-controlled active power filter is controlled to inject currents opposite to these quantities, thereby achieving the balancing function. The operation of the proposed system along with the selection of the active power filter components are discussed in detail. Finally, experimental filter operation is verified for an unbalanced load.

[449] J. F. Chicharo, D. Dejsakulrit, and B. S. P. Perera, "Centroid based switching strategy for active power filters," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 648-653, 1993.

This paper presents a new switching strategy for current-fed active power filter applications. The strategy is based on the notion of equal area criteria. In addition the centroids of both the injected current pulses and the corresponding areas of the continuous harmonic current reference waveform are constrained to occupy the same position in the time domain. In essence the method is a nonuniform sampling technique. The proposed approach provides better performance in terms of improved distortion factor characteristics when compared to equal sampling techniques. From a computational point of view, the centroid based technique is also far less demanding, by a factor of five, when compared to previously published work.

[450] N. Mutoh, K. Sakai, A. Ueda, and K. Nandoh, "Magnetic flux compensating torque control method suitable for general purpose inverters with superaudible switching frequencies," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 615-625, 1993.

A new torque control method is described that is suitable for general-purpose induction motor variable speed drives driven by superaudible frequency PWM inverters. The primary magnetic flux reference is compensated, using only current sensors, on the basis of the inverter angular frequency and the slip angular frequency so that motor torque can be generated according to load torque. The superaudible frequency PWM signals are generated by divisions of duration times of the voltage vectors, determined on the basis of the primary magnetic flux reference. Experiments showed that high-performance torque characteristics suitable for general purpose inverters could be obtained by this method.

[451] H. A. Kojori, J. D. Lavers, and S. B. Dewan, "Critical assessment of the continuous-system approximate methods for the stability analysis of a sampled data system," IEEE Transactions on Power Electronics, vol. 8, no. 1, pp. 76-84, 1993.

A critical assessment of the approximate methods for the stability analysis of a PWM static VAR compensator, which is a typical sampled data power converter system, is presented. Different continuous-system approximate models for the stability analysis of the system are developed and their validity is investigated. In particular, we will show that continuous system approximate models, in which only the principal component of the open-loop pulse transfer function is considered, cannot be used for pulsed stability analysis and closed-loop design of the system. Although these approximate analyses can be misleading and/or erroneous, a standard method such as z-domain analysis or pulse transfer function analysis in the s domain in which the sampling effect is not neglected yields useful results. In this paper, a frequency domain method based on direct computation of a pulse transfer function in the s domain is used for pulsed stability analysis. The closed-loop operation of the system with a PI controller is investigated. The dynamic performance and the closed-loop design of the system is verified with the Electro-Magnetic Transients Program (EMTP). Selected predicted results are verified experimentally on a laboratory scale prototype PWM static VAR compensator.

[452] T. C. Banwell, "155-mb/s led transmitter with integral power conditioning," IEEE Transactions on Power Electronics, vol. 8, no. 1, pp. 85-89, 1993.

There is a growing need to reduce the power consumption of the high-speed components in broadband telecommunications networks. This will require that power processing be treated simultaneously with signal processing in the development of new broadband products. The power consumption of fiber-optic transmitters, which can use either lasers or LED's, is considered to be relatively large. LED transmitters normally require considerably more operating power than lasers, which is often the deciding factor in the selection of a laser rather than an LED in short span 100-200 Mb/s fiber-optic links. The LED transmitter issue therefore represents a good opportunity for examining new strategies to improve power-hungry technologies. The overall performance of an LED transmitter can be enhanced by using the available supply voltage more efficiently through power conditioning. We demonstrate a prototype 155-Mb/s LED transmitter that achieves a threefold improvement in power efficiency.

[453] K. Harada and G. Zhao, "Controlled power interface between solar cells and ac source," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 654-662, 1993.

A novel interface circuit between solar cells and commercial ac source using Van Allen's multivibrator is presented. In this circuit, the ac source is used for a backup of solar cells, and the source and load power flow is automatically balanced by the circuit itself without any external phase control. Based on the analysis of the characteristics of solar cells and Van Allen's multivibrator, we describe 1) a new method to control the dc power from solar cells according to the current load conditions and 2) a simple and fast optimization method to derive the maximum solar power.

[454] T. M. Jahns, R. W. A. A. De Doncker, A. V. Radun, P. M. Szczesny, and F. G. Turnbull, "System design considerations for a high-power aerospace resonant link converter," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 663-672, 1993.

A new variable-speed, constant-frequency (VSCF) 400 Hz aircraft generating system has been developed using an actively clamped resonant dc link converter. The design approach used to select the best configuration for the resonant converter power stage is described, including techniques for choosing power component values to meet key governing performance specifications. Interactions between the various converter components are discussed, suggesting approaches for selecting values which must meet multiple and sometimes conflicting system performance criteria. Verification is provided using a combination of simulation results and test data from a 60 kVA laboratory breadboard system.

[455] F. M. Flinders, P. J. Wolfs, and K. C. Kwong, "Improved techniques for switching power amplifiers," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 673-679, 1993.

The control system design of a dc to 10 kHz bandwidth 45 kVA current sourced power amplifier suitable for geophysical exploration applications is presented. A five-level modulation scheme has been implemented using a modified bridge topology with only four switches. This scheme gives an order of magnitude improvement in switching ripple and control performance over two-level modulation. Using this system, a 50 kHz switch frequency allows a 20 kHz, -3 dB bandwidth to be easily achieved. Simulation as well as tenth scale model test results are presented. The current output waveform reproduction is of high quality over the rated dc to 10 kHz frequency range. The THD is 0.3% at 1 kHz.

[456] J. M. S. Kim and S. B. Dewan, "Steady-state analysis of dual converters with circulating-current mode used in four-quadrant dc magnet power supplies," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 680-687, 1993.

The dual converter with circulating-current mode has been proposed to meet the requirements of the high-performance four-quadrant dc magnet power supplies. In the power supply configuration, interconverter inductors are used to limit the circulating current and an additional low-pass filter is required to reduce output ripple content. The operation of the dual converter in this configuration is determined by many circuit parameters, including the circulating current-limiting inductors and the additional low-pass output filter. This paper presents the steady-state analysis of the dual converter operating in a circulating current mode, with an output low-pass filter, in order to identify the operating conditions of the proposed power supply configuration. The experimental results are provided to verify the analytical results.

[457] D. Czarkowski and M. K. Kazimierczuk, "Phase-controlled series-parallel resonant converter," IEEE Transactions on Power Electronics, vol. 8, no. 3, pp. 309-319, 1993.

A constant-frequency phase-controlled series-parallel resonant dc-dc converter is introduced, analyzed in the frequency domain, and experimentally verified. To obtain the dc-dc converter, two identical series-parallel resonant inverters are paralleled and the resulting phase-controlled resonant inverter is loaded by a voltage-driven rectifier. The converter can regulate the output voltage at a constant switching frequency in the range of load resistance from full-load resistance to infinity while maintaining good part-load efficiency. The efficiency of the converter is almost independent of the input voltage. For switching frequencies slightly above the resonant frequency, power switches are always inductively loaded, which is very advantageous if MOSFET's are used as switches. Experimental results are given for the phase-controlled series-parallel resonant converter with a center-tapped rectifier at an output power of 52 W and a switching frequency of 127 kHz. The measured current imbalance between the two inverters was as low as 1.2:1.

[458] S. Clemente, "Transient thermal response of power semiconductors to short power pulses," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 337-341, 1993.

Thermal response curves used to calculate the peak junction temperature of power semiconductors are normally derived by experimental identification of the parameters of a known model. Unfortunately the model, developed many years ago, is inappropriate for large surges of short time duration, as they are encountered in present day power conditioning systems. An alternative model is derived, the limits of its accuracy are estimated, and a correction factor is described. A verification of the accuracy of the two methods is also presented.

[459] C. L. Ma and P. O. Lauritzen, "Simple power diode model with forward and reverse recovery," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 342-346, 1993.

The basic diode charge-control model used in SPICE is extended by employing the lumped charge concept of Linvill to derive a set of model equations from simplified device physics. Both forward and reverse recovery phenomena are included as well as emitter recombination. The complete model requires only seven relatively simple equations and three additional device parameters beyond the generic SPICE diode model.

[460] G. Busatto, "Physical modeling of bipolar mode jfet for cae/cad simulation," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 368-375, 1993.

A circuit model of power bipolar JFET, based on a specific formulation of its charge control model, is presented. The circuit obtained accurately describes both unipolar and bipolar modes of operations of the device, and is presented in a form suitable to be incorporated in circuit CAD simulators. The model was developed on a physical basis, and its parameters can in principle be directly computed from geometrical and physical characteristics of the device. The paper also presents the implementation of the model into the version 4.02 of PSPICE obtained by modifying a device subroutine.

[461] V. A. Sankaran, J. L. Hudgins, and W. M. Portnoy, "High-energy pulse-switching characteristics of thyristors," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 347-354, 1993.

Experiments were conducted to study the high energy, high di/dt pulse-switching characteristics of SCR's with and without the amplifying gate. High di/dt, high-energy single-shot experiments were first done. Devices without the amplifying gate performed much better than the devices with the amplifying gate. A physical model is presented to describe the role of the amplifying gate in the turn-on process, thereby explaining the differences in the switching characteristics. The turn-on area for the failure of the devices was theoretically estimated and correlated with observations. This allowed calculation of the current density required for failure. Since the failure of these devices under high di/dt conditions was thermal in nature, a simulation using a finite-element method was performed to estimate the temperature rise in the devices. The results from this simulation showed that the temperature rise was significantly higher in the devices with the amplifying gate than in the devices without the amplifying gate. From these results, the safe operating frequencies for all the devices under high di/dt conditions was estimated. These estimates were confirmed by experimentally stressing the devices under high di/dt repetitive operation.

[462] K. Harada, A. Katsuki, and M. Fujiwara, "Use of esr for deterioration diagnosis of electrolytic capacitor," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 355-361, 1993.

An electrolytic capacitor is often utilized for smoothing the output of a switching regulator. In this case, the electrolytic capacitor usually has the shortest span of life in the power supply, and then determines the system lifetime. Therefore, a deterioration diagnosis of the electrolytic capacitor is needed for preventive maintenance of the circuit. In this paper, a new diagnostic method is proposed for applicability to the output smoothing capacitor of a forward-type converter and a buck-boost converter. With this method, the electrolytic capacitor life-cycle aging rate can be projected for the active circuit over the system life.

[463] D. C. Hamill, "Lumped equivalent circuits of magnetic components: The gyrator-capacitor approach," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 97-103, 1993.

In place of the conventional reluctance-resistance analogy for forming lumped equivalent circuits of inductive components, a permeance-capacitance analogy is advocated. In this approach, magnetic paths are modeled by capacitive circuits and windings are represented by gyrator two-ports. The technique is applied to the integrated magnetics of a zero-ripple isolated Cuk dc-dc converter, allowing its electrical and magnetic circuits to be simultaneously simulated with SPICE.

[464] P. J. Wolfs, G. F. Ledwich, and K. C. Kwong, "Application of the duality principle to nonplanar circuits," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 104-111, 1993.

The principle of duality has been widely used in the development and understanding of power electronic converter topologies. It has been widely believed that the duality principle cannot be applied to nonplanar circuits. This paper shows how the duality principle can be applied to nonplanar circuits such as three-phase bridge converters and their loads. While the direct duals have restricted utility, they provide some insight into the formation of three-phase conversion circuits that ultimately allow several new converters to be developed. These include new frequency converters, a three-phase sinusoidal input current SMPS, and an SMPS with a three-phase high-frequency link. Some control techniques and supporting simulation results are presented.

[465] N. Yamashita, K. Tsukamoto, and T. Yachi, "Board-mounted power supply module using a new low power dissipation-control ic," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 362-367, 1993.

This paper presents a board-mounted power supply module for telecommunications systems. The module uses a newly developed control IC to achieve higher efficiency and better compactness. The IC mainly consists of CMOSFET's to reduce power dissipation. The output driver for the main switch has been improved by regulating the swing voltage and optimizing the output-MOSFET channel width. The newly designed internal regulator in the IC has an extra input from a third winding on the transformer and supplies regulated voltage using either input. The IC consumes one-fourth of the power of a conventional control IC. To minimize the size of the power supply module, the IC integrates and perfectly isolates a primary circuit, a secondary circuit, a start-up, and an alarm activator using dielectric isolation. Using the IC, a 3-W power supply module with 80% efficiency is developed.

[466] A. R. Hefner and D. L. Blackburn, "Simulating the dynamic electrothermal behavior of power electronic circuits and systems," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 376-385, 1993.

A methodology is presented for simulating the dynamic electrothermal behavior of power electronic circuits and systems. In the approach described, the simulator solves for the temperature distribution within the semiconductor devices, packages, and heatsinks (thermal network) as well as the currents and voltages within the electrical network. The thermal network is coupled to the electrical network through the electrothermal models for the semiconductor devices. The electrothermal semiconductor device models calculate the electrical characteristics based upon the instantaneous value of the device silicon chip surface temperature and calculate the instantaneous power dissipated as heat within the device. The thermal network describes the flow of heat from the chip surface through the package and heatsink and thus determines the evolution of the chip surface temperature used by the semiconductor device models. The thermal component models for the device silicon chip, packages, and heatsinks are developed by discretizing the nonlinear heat diffusion equation and are represented in component form so that the thermal component models for various packages and heatsinks can be readily connected to one another to form the thermal network.

[467] W. Tang, F. C. Lee, R. B. Ridley, and I. Cohen, "Charge control: Modeling, analysis, and design," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 396-403, 1993.

Characteristics of charge control are studied here. A complete small-signal analysis is performed for the control scheme. Subharmonic oscillation similar to that of peak current-mode control is found, and the relationship between subharmonic oscillation and line/load condition of charge control is defined. Based on analysis, design guidelines which guarantee the stability of the control system under given line and load ranges are proposed. The small-signal model was confirmed experimentally.

[468] W. Tang, F. C. Lee, and R. B. Ridley, "Small-signal modeling of average current-mode control," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 112-119, 1993.

A recently proposed average current-mode control is analyzed. A complete small-signal model for the control scheme is developed. The model is accurate up to half the switching frequency. This control scheme is suitable for applications where the average inductor current needs to be controlled, as in power factor correction circuits and battery charger/dischargers. The subharmonic oscillation, commonly found in peak current-mode control, also exists in this control. This subharmonic oscillation can be eliminated by choosing a proper gain of the compensation network in the current loop. Model predictions are confirmed experimentally.

[469] J. L. Freitas Vieira and I. Barbi, "Constant frequency pwm capacitor voltage-clamped series resonant power supply," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 120-126, 1993.

This paper proposes a capacitor voltage clamped series resonant converter, regulated at constant frequency by pulse-width modulation (PWM-CVC-SRC), suitable for an off-line isolated multiple output power supply. The principle of operation, theoretical analysis, simulation, design procedure, and design example are provided, along with experimental results. The validity of the theoretical analysis and the main properties of the proposed converter were demonstrated in the laboratory, with the design and construction of an isolated power supply rated at 12 V/16 A, operating at 100 kHz. The proposed technique propitiates a significant reduction in the rms value of the current through transistors, besides the reduction of the size of the output filter capacitor and dynamic response improvements.

[470] R. Oruganti and T. C. How, "Resonant-tank control of parallel resonant converter," IEEE Transactions on Power Electronics, vol. 8, no. 2, pp. 127-134, 1993.

A new control method - resonant-tank control (RTC) - is proposed for a parallel resonant converter operating above resonance. Using a simple linear combination of tank variables, it has potential for high-frequency dc-dc converter applications. RTC controls the tank in a near time-optimal manner and is shown to have better dynamics compared to conventional frequency control. Experimental results to confirm the superior transient performance of the RTC method are provided. The principle of operation of the RTC may be extended to operation below resonance as well as to series resonant converter control.

[471] M. K. Kazimierczuk and W. Szaraniec, "Electronic ballast for fluorescent lamps," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 386-395, 1993.

A frequency-domain analysis is given for a Class D voltage-switching power inverter with a load resistance connected in parallel with a resonant capacitor. Using the fundamental component approximation, design equations are derived to provide easy-to-use design tools. The inverter is inherently short-circuit proof, but cannot operate safely with an open circuit at the resonant frequency. Safe operation with an open circuit can be achieved if the operating frequency is sufficiently lower or higher than the resonant frequency. The experimental results are given for two fluorescent lamps F40 connected in series, using MTP5N40 MOSFET's. The operating frequency was 50 kHz at full power and 70 kHz at 20% of full power. The power factor was 0.99 at full power and 0.96 at 20% of full power. At full power, the efficiency of the Class D inverter was 95.6% and the efficiency of the power factor corrector was 93%. The overall efficiency of the ballast was 89.4% at full power.

[472] K. Harada, A. Katsuki, M. Fujiwara, H. Nakajima, and H. Matsushita, "Resonant converter controlled by variable capacitance devices," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 404-410, 1993.

A new device of variable capacitance is proposed. And its applications to the output voltage regulation of resonant converters are presented. The new device has an independent input terminal for controlling its capacitance. The converters used here are the well-known Schwarz circuit and the buck-type current-resonant converter with the resonant switch. By applying the devices to the capacitors in the LC resonant tanks, the resonant converters can be regulated with the switching frequency fixed.

[473] R. Farrington, M. M. Jovanovic, and F. C. Lee, "Design oriented analysis of reactive power in resonant converters," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 411-422, 1993.

The effectiveness of resonant converters can be evaluated on the amount of processed reactive power relative to the output power. A number of resonant converters are analyzed to derive the reactive power and rms current circulating through the transformer. The results of the analysis are used to define design guidelines that minimize the circulating energy in the converters and maximize their efficiencies and power densities. The described analysis and design considerations can be easily extended to other resonant and soft-switching topologies.

[474] A. K. S. Bhat, "Analysis and design of a modified series resonant converter," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 423-430, 1993.

A modified series resonant converter (SRC) (also referred to as LCL-type SRC) which overcomes the problems of standard series resonant converter is presented. State-space approach is used for the analysis. Analysis shows that the converter enters into three different modes. Converter gain and other component stresses are plotted with variation in the load current. Detailed experimental results obtained from a 500 W, MOSFET converter are presented to verify the theory. With a proper selection of inductor ratio, only a narrow variation in switching frequency is required to regulate the output voltage for wide variation in the load current. It is shown that by placing the parallel inductor on the secondary side, the parasitics of the high-frequency transformer can be used profitably.

[475] R. L. Steigerwald, W. Roshen, and C. F. Saj, "High-density 1 kw resonant power converter with a transient boost function," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 431-438, 1993.

A series/parallel resonant dc-dc converter with secondary-side resonance and a novel input `boosting' feature is described. In order to greatly reduce the conduction loss (factor of 4) due to circulating currents in the resonant components, the boost circuit, which requires no additional active switches, operates only when needed during transient input voltage dips. This reduces the effective input voltage range over which the converter must operate and allows optimization at the steady-state input voltage. The converter employs highly efficient resonant inductors and novel z-folded thin flex circuit transformer windings in order to meet a density of greater than 50 W/in³ with an efficiency approaching 95%. The dc-dc converter was developed for use as a 270 to 50 V line converter for distributed power applications.

[476] D.-Y. Huh and G.-H. Cho, "Electronic step down (220/110 v) transformer using a new quantum series resonant converter," IEEE Transactions on Power Electronics, vol. 8, no. 4, pp. 439-444, 1993.

A new Quantum Series Resonant Converter (QSRC) topology for pure sinewave 60 Hz ac chopper is proposed. It has three bidirectional switches and operates at high switching frequency with low switching loss. Bidirectional power flow is possible and the switches can operate at either zero current switching (ZCS) mode or zero voltage switching (ZVS) mode by slight modification. The QSRC is thought to be suitable for such a system with fixed voltage conversion ratio. The proposed converter is applied to an electronic 220/110 V transformer. The detailed analyses and the experimental results for 1 kVA are presented.

[477] K. Harada and K. Harada, "Novel circuit for dead angle compensation in the dc-to-dc converter controlled by a magnetic amplifier," IEEE Transactions on Power Electronics, vol. 9, no. 2, pp. 220-224, 1994.

A novel circuit for compensating the dead angle in the dc-to-dc converter controlled by a magnetic amplifier is presented. The proposed circuit suppresses the dead angle so that the core loss may be reduced. The behavior of this circuit is explained analytically and a condition for compensation is derived theoretically. By adding this compensation circuit, excellent control characteristics of the converter are obtained without spoiling the current surge suppression characteristics of the magnetic amplifier.

[478] F. Lin and D. Y. Chen, "Reduction of power supply emi emission by switching frequency modulation," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 132-137, 1994.

The effect of frequency modulation on power supply EMI noise is investigated. Significant reduction of emission is possible with this scheme.

[479] T. Farkas and M. F. Schlecht, "Viability of active emi filters for utility applications," IEEE Transactions on Power Electronics, vol. 9, no. 3, pp. 328-337, 1994.

The application of active circuitry to increase the performance per size and cost of utility-side EMI filters is considered. The major problems are power line frequency (60 Hz) rejection and the compensation of the feedback loop, which is influenced by the wide-ranging utility impedance. While analysis and simulations show that these problems prevent the practical application of active filtering to power supplies switching at around 75 kHz, results at 450 kHz demonstrate potential for substantial improvement of EMI filters for switching frequencies of a few hundred kHz, although with the cost of a complex compensation.

[480] A. Mertens, H.-C. Skudelny, P. P. A. Caldeira, and T. Lipo, "Characterization of gto's under different modes of zero current switching," IEEE Transactions on Power Electronics, vol. 9, no. 3, pp. 338-345, 1994.

In recent years, several papers described the use of GTO's in zero current switching (ZCS) applications, with the goal of increasing the frequency range for medium- and high-power converters. Zero current switching with GTO's can be applied in series and parallel resonant converters, as well as in PWM inverters with commutation aid networks. The voltage and current waveforms at the devices differ in each of these applications, and different modes of ZCS can be identified. In this paper, a comparative view of the behavior and characteristics of the GTO in the different modes of ZCS is presented. The variety of ZCS waveforms is described and transferred into a unifying schematic. The behavior of GTO's in the different modes of operation is characterized, and requirements to the circuit environment are pointed out. The relations between the most important circuit parameters and some of the device waveform parameters are investigated experimentally.

[481] K.-w. Ma and Y.-s. Lee, "Technique for sensing inductor and dc output currents of pwm dc-dc converter," IEEE Transactions on Power Electronics, vol. 9, no. 3, pp. 346-353, 1994.

The design, analysis and trade-offs of a novel method to sense the inductor and dc output currents of PWM converters are presented. By sensing and adding appropriately the currents in the transistor, rectifier and capacitors of a converter using current transformers, the waveforms of inductor and dc output currents can be reconstructed accurately while maintaining isolation. This method offers high bandwidth, clean waveform, practically zero power dissipation and simple circuit. The technique is applicable to all PWM converters in both continuous and discontinuous modes, and is most suitable for the implementation of current mode control schemes like hysteretic, PWM conductance control, and output current feedforward. This approach has been experimentally verified at a wide range of current levels, duty cycles, and switching frequencies up to 1.4 MHz.

[482] Y.-F. Liu and P. C. Sen, "General unified large signal model for current programmed dc-to-dc converters," IEEE Transactions on Power Electronics, vol. 9, no. 4, pp. 414-424, 1994.

A general and unified large signal averaged circuit model for current programmed DC-to-DC converters is proposed. In the averaged circuit model, the active switch is modeled by a current source, with its value equal to the averaged current flowing through it, and the diode is modeled by the voltage source, with its value equal to the averaged voltage across it. The averaged circuit model has the same topology as the switching converter. The large signal averaged circuit model for current programmed Buck, Boost, Buck-Boost and Cuk converters are proposed, from which the large signal characteristics can be obtained. The steady-state and small signal transfer functions of the current programmed DC-to-DC converters can all be derived from their large signal averaged circuit models. The large signal characteristics of current programmed Buck converter are studied by both the phase plane trajectory and the time domain analysis. Experimental prototypes for a current programmed Buck converter, with and without an input filter, are breadboarded to verify the analysis.

[483] K. Smedley and S. Cuk, "Switching flow-graph nonlinear modeling technique," IEEE Transactions on Power Electronics, vol. 9, no. 4, pp. 405-413, 1994.

A unified graphical modeling technique, `Switching Flow-Graph' is developed to study the nonlinear dynamic behavior of pulse-width-modulated (PWM) switching converters. Switching converters are variable structure systems with linear subsystems. Each subsystem can be represented by a flow-graph. The Switching Flow-Graph is obtained by combining the flow-graphs of the subsystems through the use of switching branches. The Switching Flow-Graph model is easy to derive, and it provides a visual representation of a switching converter system. Experiments demonstrate that the Switching Flo w-Graph model has very good accuracy.

[484] A. M. Trzynadlowski and S. Legowski, "Application of neural networks to the optimal control of three-phase voltag e-controlled inverters," IEEE Transactions on Power Electronics, vol. 9, no. 4, pp. 397-404, 1994.

A novel concept of application of neural networks for generation of optimal switching patterns in voltage-controlled inverters is described. The pulsewidth modulator (PWM), based on hardware analog neural networks, responds with high accuracy to any desired value of the modulation index. No microprocessor or large memory typical for the existing optimal PWM schemes is required. Theoretical analysis of the proposed so-called sparse neural network is provided, and experimental results that confirm the high performance and technical advantages of the developed modulator are presented.

[485] D. Metzner, T. Vogler, and D. Schroeder, "Modular concept for the circuit simulation of bipolar power semiconductors," IEEE Transactions on Power Electronics, vol. 9, no. 5, pp. 506-513, 1994.

Physical network simulation models of bipolar power devices strongly depend on an accurate description of the low-doped drift zone, because the behavior of the diffusion charge in this region governs the static and dynamic device characteristics. In this paper a one-dimensional modeling module for the drift zone is presented, which accounts for all important effects under high injection conditions: Nonquasistatic ambipolar diffusion, temperature- and injection-level dependent scattering and recombination effects as well as impact ionization. When combined with well known expressions describing the rest of the respective structure, very accurate and CPU-time efficient network models can be implemented, that are suited for all applications including resonant modes (ZVS, ZCS, ZVT). The module is incorporated in a commercially available network simulator and used so far for modeling the IGBT, the high power diode and the GTO. Models for the BJT, FCTh, SITh, and MCT will follow.

[486] M. Rosling, H. Bleichner, K. Nordgren, F. Vojdani, and E. Nordlander, "Study of design influence on anode-shorted gto thyristor turn-on and turn-off," IEEE Transactions on Power Electronics, vol. 9, no. 5, pp. 514-521, 1994.

Anode-shorted GTO thyristor samples were investigated by means of the free-carrier absorption (FCA) technique. Both the turn-on and turn-off processes were investigated as regards the two-dimensional carrier distribution for different stages of the transient cycles. The results are presented as carrier-map sequences, i.e., 3-D pictures of measured 2-D carrier distributions. Samples were formed as unit segments cut out from large-area devices, and associated with different degree of anode shorting, silicon thickness, and lifetime treatment. During investigation, the samples were inductively anode loaded, and as regards the turn-off process they were operated near the safe-operation limit. The measurements clearly illustrate the way carriers are transported in the sample when firing the device, and the turn-on process is visualized in steps by means of carrier-map sequences. These measurements are supported by computer simulations. The turn-off process is also visualized in carrier-map sequences measured from two perpendicular directions, and the maps show the critical electric-field expansion which always precedes a turn-off failure due to dynamic breakdown mechanisms. Further on, the effect of design-parameter variations, e.g., anode shorting pattern and carrier lifetime reductions, on destructive GTO turn-off phenomena are discussed.

[487] F. Caricchi, F. Crescimbini, and T. A. Lipo, "Converter topology with load-neutral modulation for trapezoidal-emf pm motor drives," IEEE Transactions on Power Electronics, vol. 9, no. 2, pp. 232-239, 1994.

The average torque of concentrated winding PM machines can be increased significantly by supplying current waveforms matching in full the trapezoidal back EMF. However, such current supply arrangements involve a large harmonic current flowing into the machine neutral. This paper presents an innovative converter topology to overcome the problem. This new configuration extends the standard layout of conventional PWM-VSI by adding a fourth branch devoted to control the voltage of the machine neutral. The inverter modes of operation resulting from the modulation of the machine neutral are discussed, and the paper reports the experimental results achieved from a converter prototype which has been constructed using IGBTs. Results show that the new inverter configuration allows significant benefits in the machine average torque, as well as the fact that the machine neutral modulation introduces an additional degree of freedom in the machine torque control.

[488] N. Kawakami, M. Hombu, T. Ikimi, A. Ueda, J. Takahashi, and K. Kamiyama, "Quick response and low-distortion current control for multiple inverter-fed induction motor drives," IEEE Transactions on Power Electronics, vol. 9, no. 2, pp. 240-247, 1994.

This paper describes a PWM control method to balance two unit inverter currents and to reduce the distortion of motor currents in a multiple GTO inverter for large capacity ac variable-speed drive systems. For an 11-kW induction motor driven by a 15-kVA multiple inverter, the imbalance current can be reduced to less than 5% of the rated motor current, and the motor current waveform can be made very close to sinusoidal. The GTO switching frequency in the multiple inverter can be lowered to one-quarter of that in the single inverter. In a 2750-kVA GTO inverter drive system which was developed based on the 15-kVA multiple inverter, excellent performance is obtained including unity power factor operation at an ac power source, smooth 4-quadrant operation, and quick speed response of 85 rad/s. The quick response is realized by field-oriented control with decoupling control between torque and exciting currents, and direct control of three-phase ac currents. In the future, the multiple GTO inverter is expected to be applied to rolling mill drives instead of cycloconverters.

[489] M. Schroedl and P. Weinmeier, "Sensorless control of reluctance machines at arbitrary operating conditions including standstill," IEEE Transactions on Power Electronics, vol. 9, no. 2, pp. 225-231, 1994.

Reluctance machines with three-phase stator windings and damperless rotors are usually operated in a closed-loop rotor-oriented control. The necessary position encoder reduces robustness considerably. In order to replace this sensor by a position-detecting algorithm based on electrical measurements, two methods are presented, well-suited to low velocity (INFORM model) and high velocity (EMF model), respectively. Based on this information, a Kalman filter yields estimates of the machine state. A rotor-oriented controller enables highly dynamic operation even at standstill. Measurements verify the good static and dynamic properties of the drive in speed-controlled mode.

[490] G. Hua, C.-S. Leu, Y. Jiang, and F. C. Y. Lee, "Novel zero-voltage-transition pwm converters," IEEE Transactions on Power Electronics, vol. 9, no. 2, pp. 213-219, 1994.

To date, soft-switching techniques applied to the PWM converters, with the exception of a few isolated cases, are subjected to either high switch voltage stresses or high switch current stresses, or both. A new class of zero-voltage-transition PWM converters is proposed, where both the transistor and the rectifier operate with zero-voltage switching and are subjected to minimum voltage and current stresses. Breadboarded converters are constructed to verify the novelty of the proposed new family of converters.

[491] R. Tymerski, "Application of the time-varying transfer function for exact small-signal analysis," IEEE Transactions on Power Electronics, vol. 9, no. 2, pp. 196-205, 1994.

An analysis method for determining the control-to-output linearized describing function of time-interval-modulated switched networks using time-varying system theory was previously proposed by the author. A simplification is now presented which eases the analysis considerably. Use of the simplified approach is demonstrated in the derivation of the control-to-output frequency response of pulse-width-modulated (PWM) dc-to-dc switching power converters operating in discontinuous conduction mode (DCM) and current programmed converters operating in continuous conduction mode (CCM) as well as in DCM. Experimental results are presented which verify the modeling approach.

[492] D. Vincenti, H. Jin, and P. Ziogas, "Design and implementation of a 25-kva three-phase pwm ac line conditioner," IEEE Transactions on Power Electronics, vol. 9, no. 4, pp. 384-389, 1994.

In this paper, an improved version of PWM AC line conditioners is proposed. As compared to previously reported structures, it uses fewer standard switch modules. This, in combination with less stringent gating requirements, improves the overall operating reliability of the system. In addition, it retains the same advantages of a regular force-commutated AC line conditioner, including sinusoidal input-output waveforms, fast dynamic response, and small input-output filters. The operating principle of the proposed structure is discussed, and the voltage feedback loop design is analyzed. Results from a 25-kVA experimental setup are provided for verification.

[493] D.-H. Jang and J.-S. Won, "Voltage, frequency, and phase-difference angle control of pwm inverters-fed two-phase induction motors," IEEE Transactions on Power Electronics, vol. 9, no. 4, pp. 377-383, 1994.

A phase-difference angle (PDA) controlled pulsewidth-modulated (PWM) inverter is proposed for adjustable speed drive for the two-phase induction motors. Output waveforms are fixed over the whole operating range of the motor. The motor torque is controlled not by the modulation of the phase voltage, but by the PDA. Based on the selected harmonic elimination (SHE) PWM technique, the commutation angles of the output voltage are calculated. Several characteristics of the two-phase induction motor driven by the PDA inverter are analyzed. Second, a hybrid PWM inverter is proposed also to compensate for the degradation of the efficiency at small PDA. Not only the PDA but also the voltage amplitude and frequency are used as the parameters for controlling the torque of the motor in the hybrid inverter. The speed characteristics of the two-phase induction motor driven by the hybrid PWM inverter are more flexible than when the motor in driven by the conventional PWM inverter, which requires adjustable communication angles.

[494] R. W. De Doncker, "Parameter sensitivity of indirect universal field-oriented controllers," IEEE Transactions on Power Electronics, vol. 9, no. 4, pp. 367-376, 1994.

The paper presents the derivation of generalized steady state torque and flux expressions for the detuned operation of an indirect universal field oriented (IUFO) controller. These expressions are represented graphically as a function of the input command ratios. With the use of these graphs, the steady state performance of all IUFOs (controlling rotor flux, airgap flux, or stator flux) can be readily evaluated.

[495] R. W. De Doncker, F. Profumo, and M. Pastorelli, "Self-tuning of tapped stator winding induction motor servo drives using the universal field-oriented controller," IEEE Transactions on Power Electronics, vol. 9, no. 4, pp. 357-366, 1994.

The paper describes a universal field oriented (UFO) controller that can operate both in a direct or indirect field orientation mode. Direct UFO control is realized by sensing amplitude and position of the airgap flux space vector using center taps on two machine windings. In the indirect mode, the rotor time remains constant and is set to the last tuned value of the previous direct field orientation mode. This proposed field controller can be realized at minimal costs in ac servo drives requiring motion control or accurate speed control.

[496] M. I. C. Simas and J. C. Freire, "Cad tools to optimize power mosfet performance using channel reverse conduction," IEEE Transactions on Power Electronics, vol. 9, no. 5, pp. 522-531, 1994.

In this paper, a contribution to the characterization of power MOS transistors under optimized switching behavior is presented. This behavior is shown to be appropriate for improving the performance of new high frequency power processing topologies. Reverse conduction through the channel resistance is imposed, thus avoiding the problem of integral diode recovery time without resorting to external diodes. Control circuit design is discussed. Advantages and drawbacks are analyzed and tested in a series resonant converter. An insight into MOSFET reverse conduction modeling is presented, aimed at the development of an accurate model for computer aided design of topologies using MOSFET's bidirectional paths. Simulation results are shown to prove the accuracy of the model.

[497] S. Masukawa and S. Iida, "Method for reducing harmonics in output voltages of a double-connected inverter," IEEE Transactions on Power Electronics, vol. 9, no. 5, pp. 543-550, 1994.

A new method for reducing harmonics involved in output voltages of the double-connected inverter is proposed. By adding four auxiliary switching devices and an interphase transformer with secondary winding to the conventional 12-step inverter, output voltages of the proposed circuit can be almost the same waveforms as a conventional 36-step inverter. In this paper, circuit performances and output voltage waveforms are discussed, and the optimum parameters are derived. Then, effects on harmonic reductions can be clarified by theoretical and experimental results, and ratings of system components are investigated.

[498] H. S.-h. Chung and A. Ioinovici, "Fast computer-aided simulation of switching power regulators based on progressive analysis of the switches' state," IEEE Transactions on Power Electronics, vol. 9, no. 2, pp. 206-212, 1994.

A new method for time-domain analysis of power electronics circuits is developed based on the following principles: a) at each instant, the switching topology is a linear time-invariant circuit; b) at each instant, the voltage across a capacitor and the current through an inductor have a certain value, like an independent voltage- or current source, respectively; c) generally, no switching relationship between the externally and internally controlled switches may be assumed; d) prior knowledge of the internally controlled switches' operation is not available; and e) the switching action may change the response of the circuit immediately after the switching moment, implying that some constraints may be in violation of the presumed switches' states. The algorithm is based on solving a system of algebraical modified nodal equations at each integration step. The number of systems to be solved equals the number of topologies the converter goes through in a cycle. This feature, and the fact that no solutions of time-differential equations or Laplace transform inverses are required, cause the algorithm to be a fast one. At each step, the presumed state of all the switches is checked, and if some constraints are violated, the program looks for another valid topology. An example, with parasitic effects taken into account, is presented; the experimental results, as well as the simulation results obtained by using other available algorithms, confirmed the accuracy of the results achieved with the presented approach.

[499] M. M. Swamy and A. K. S. Bhat, "Comparison of parallel resonant converters operating in lagging power factor mode," IEEE Transactions on Power Electronics, vol. 9, no. 2, pp. 181-195, 1994.

Three different Parallel Resonant Converter (PRC) configurations are compared for their performance. The discontinuous capacitor voltage mode is emphasized in the comparison and is shown not to exist in the case of PRC with the resonating capacitor on the primary side of the high-frequency (HF) transformer. It is further shown here that the condition for discontinuous capacitor voltage (DCV) mode in case of a PRC with the assumption of an ideal HF transformer and a PRC with secondary-side resonance differ only in the ratio M/(M + L + L_p), which is equal to 1.0 for PRC's with the assumption of an ideal HF transformer. The comparison study shows that the PRC with the resonating capacitor on the primary side of a nonideal HF transformer is more appropriate for low-voltage high-current applications, while the PRC with resonating capacitor on the secondary side of a nonideal HF transformer is better suited to supply large-voltage medium- and low-current loads. Experimental results obtained from prototype units designed and built are presented to support the theory.

[500] J. A. Ferreira, "Improved analytical modeling of conductive losses in magnetic components," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 127-131, 1994.

The one well-known one-dimensional method for calculating the ac resistance of multilayer windings contains a built-in orthogonality which has not been reported previously. Orthogonality between skin effect and proximity effect makes a more generalized approach for the analytical solution of ac resistance in windings possible. This includes a method to calculate the ac resistance of round conductor windings which is not only convenient to use, but gives more accurate answers than the basic one-dimensional method because the exact analytical equations for round conductors can be used.

[501] W. G. Hurley and D. J. Wilcox, "Calculation of leakage inductance in transformer windings," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 121-126, 1994.

A formula is presented to calculate mutual impedance between transformer windings on ferromagnetic cores. The formula is based on the solution of Maxwell's Equations for coils on ferromagnetic cores and as such offers the ultimate in accuracy. The formula is frequency dependent, taking into account the effect of eddy currents in the core on the flux distribution as well as representing the eddy current core loss as an equivalent resistance. Experimental results are presented for leakage inductance and an illustrative example is presented showing how leakage inductance affects the operation of a typical switching mode power supply. Approximations for the formula are also presented to simplify the calculations under certain operating conditions.

[502] H. Morel, S. H. Gamal, and J. P. Chante, "State variable modeling of the power pin diode using an explicit approximation of semiconductor device equations: A novel approach," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 112-120, 1994.

The concepts of state variable modeling have been applied to obtain a general circuit like model for the power PIN diode. The main aim of this paper is to demonstrate the feasibility of the state variable modeling approach for the PIN diode. From simplified semiconductor device differential equations, the model is built with the corresponding variational equation using an internal approximation. With a special choice of the decomposition functional basis of such internal approximation, it was possible to get efficient and reliable models for the reverse recovery. A simple model of three state variables that has only six parameters, most of which are technological, represented a major improvement in describing circuit/device waveforms during reverse recovery.

[503] H. Akagi, "Trends in active power line conditioners," IEEE Transactions on Power Electronics, vol. 9, no. 3, pp. 263-268, 1994.

Active power line conditioners, which are classified into shunt and series ones, have been studied with the focus on their practical installation in industrial power systems. In 1986, a combined system of a shunt active conditioner of rating 900 kVA and a shunt passive filter of rating 6600 kVA was practically installed to suppress the harmonics produced by a large capacity cycloconverter for steel mill drives. More than one hundred shunt active conditioners have been operating properly in Japan. The largest one is 20 mVA, which was developed for flicker compensation for an arc furnace with the help of a shunt passive filter of 20 mVA. In this paper, the term of `active power line conditioners' would be used instead of that of `active power filters' because active power line conditioners would cover a wider sense than active power filters. The primary intent of this paper is to present trends in active power line conditioners using PWM inverters, paying attention to practical applications.

[504] W. H. Kwon and G. H. Cho, "Optimum quantum sequence control of quantum series resonant converter for minimum output voltage ripple," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 74-84, 1994.

A new control scheme named optimum quantum sequence control (OQSC) which always minimizes the output voltage ripple of the quantum series resonant converter (QSRC) for all possible sequences is proposed. This control scheme is so general that it is irrelevant to all circuit conditions such as magnitudes of circuit elements as well as input/output voltage so far as it is operating in the continuous conduction mode (CCM). Further more the dynamic range of QSRC is much extended by the OQSC. This feature is verified by simulations and experiments with good agreements.

[505] R. A. Wunderlich and P. K. Ghosh, "Modeling the gate more accurately for power mosfets," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 105-111, 1994.

In recent years, power MOSFET devices are replacing the bipolar transistor. However, the power MOSFET is a fairly new device and current modeling techniques have not produced an accurate simulation of the gate to source. The method presented here generated a more accurate model of the transient behavior and gate to source characteristics of the power MOSFET. The results provide a better correlation between the MOSFET model and the actual device.

[506] S. Hiti, V. Vlatkovic, D. Borojevic, and F. C. Y. Lee, "New control algorithm for three-phase pwm buck rectifier with input displacement factor compensation," IEEE Transactions on Power Electronics, vol. 9, no. 2, pp. 173-180, 1994.

A new control algorithm for the three-phase buck rectifier with an input filter is developed. The algorithm employs a separate control loop for compensation of the input current displacement factor in steady-state, in addition to the standard output voltage regulation loop. The algorithm allows separate design of the input filter and of closed-loop output voltage control. The design procedure is explained and illustrated with an example. The algorithm is verified experimentally on a 1 kW, 100 kHz, three-phase isolated buck converter.

[507] J. W. Kolar, H. Ertl, and F. C. Zach, "Novel three-phase single-switch discontinuous-mode ac-dc buck-boost converter with high-quality input current waveforms and isolated output," IEEE Transactions on Power Electronics, vol. 9, no. 2, pp. 160-172, 1994.

In this paper, a new three-phase single-switch ac-dc flyback converter system is presented. The system operates in the discontinuous mode. The simple structure of its power and control circuit, low mains current distortion, and resistive fundamental behavior, as well as the high-frequency isolation of the controlled output voltage, have to be pointed out. Besides the analysis of the stationary operating behavior, the dependencies of the peak values, average values, and rms values of the device currents, and of the maximum blocking voltages across the power electronic devices on the circuit parameters, are given as analytic approximations. The theoretical analysis is verified by digital simulation.

[508] D. R. Veas, J. W. Dixon, and B.-T. Ooi, "Novel load current control method for a leading power factor voltage source pwm rectifier," IEEE Transactions on Power Electronics, vol. 9, no. 2, pp. 153-159, 1994.

A novel PWM voltage source rectifier, controlled by the load dc current instead of the dc voltage, has been developed. Its main characteristics are: a) there is neither input current sensors nor dc voltage sensor; b) it works with an unchangeable and predefined PWM pattern; c) it presents a very strong stability; d) its stability does not depend on the size of the dc capacitor; e) it can work at leading power factor for all load conditions, and f) it can also work with zero regulation for all load conditions. Digital simulations, analyses, and experiments confirm all these characteristics of the control method.

[509] J. Nastran, R. Cajhen, M. Seliger, and P. Jereb, "Active power filter for nonlinear ac loads," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 92-96, 1994.

This paper describes an active power filter for nonlinear ac loads with the power part carried out in the bridge connection. A theoretical approach to the implementation of the current reference is given for this original solution of the serial active filter. The paper also provides experimental results of the filter application on two specific nonlinear loads, i.e., on the ohmic load, fed over a pair of antiparallel thyristors, and on the accumulator feeder.

[510] L. Rossetto, G. Spiazzi, P. Tenti, B. Fabiano, and C. Licitra, "Fast-response high-quality rectifier with sliding mode control," IEEE Transactions on Power Electronics, vol. 9, no. 2, pp. 146-152, 1994.

A PWM rectifier including an uncontrolled rectifier and a Cuk converter stage driven by a sliding mode controller is described. Like other high-quality rectifiers, this solution allows low-distorted and in-phase line current. Moreover, due to the sliding mode control, fast and stable response is achieved, in spite of the large output filter. Control complexity is the same as that of standard current-mode controls. Converter analysis, design criteria, and experimental results are reported.

[511] A. C. Tsui, H. Yilmaz, F. I. Hshieh, M. Chang, and T. Fortier, "Commutating soa capability of power dmos fet's," IEEE Transactions on Power Electronics, vol. 9, no. 2, pp. 141-145, 1994.

The commutating safe operating area (CSOA) of DMOS FET's is determined by the peak reverse-recovery current and the peak reapplied voltage. Both contribute to the triggering of localized turn-on of the built-in bipolar junction transistor (BJT). New DMOS FET's with lower bipolar gain and shorter minority-carrier lifetime have doubled the CSOA capability.

[512] I. Batarseh, "Resonant converter topologies with three and four energy storage elements," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 64-73, 1994.

Generalized half-bridge and full-bridge resonant converter topologies with two, three and four energy storage elements are presented. All possible circuit topologies for such converters under voltage/current driven and voltage/current sinks are discussed. Many of these topologies have not been investigated in open literature. Based on their circuit element connections and source and load excitation types, these topologies are classified into resonant and non-resonant topologies and on their physical realizability. Comparison based on exact steady state analysis are given for typical second- and third-order series resonant converters whereas the fourth-order topology is based on the approximate analysis.

[513] J. M. Simonelli and D. A. Torrey, "Alternative bus clamp for resonant dc-link converters," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 56-63, 1994.

This paper presents an alternative circuit configuration for clamping the link voltage in a resonant dc-link converter. The alternative circuit is a lossless clamp which allows for totally autonomous control of the clamp voltage and resonant link under all operating conditions. The clamp is comprised of two capacitors, three controllable switches and three diodes. The clamp does not require the use of external bias supplies for startup or no-load operation. Control of the input and/or output waveforms for a converter employing this circuit remains virtually identical to that for the resonant dc-link inverter (RDCLI). An analysis of clamp operation is performed detailing its modes of operation. From this analysis, insight is gained into the appropriate selection of clamp capacitors. Simulations and experimental results are presented to corroborate the analysis. The control of the clamp is discussed in detail.

[514] A. M. Trzynadlowski and S. Legowski, "Minimum-loss vector pwm strategy for three-phase inverters," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 26-34, 1994.

A novel vector PWM method for three-phase voltage-controlled inverters is described. The so-called Minimum-Loss Vector PWM (MLVPWM) strategy is characterized by the minimum amount of switching losses incurred in the inverter switches. Comparative analysis proving superiority of the MLVPWM technique over the existing regular-sampling PWM methods, and results of experimental investigation of a prototype modulator are presented.

[515] C.-T. Pan and T.-Y. Chang, "Improved hysteresis current controller for reducing switching frequency," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 97-104, 1994.

In this paper, an improved hysteresis current controller is proposed. It coordinates the switching of the three-phase switches in the d-q phase plane. In addition to the current error, information of the current error derivative is further employed so that one can take more advantage of adding the zero voltage vector for reducing the switching frequency. A simple hardware implementation of the improved hysteresis current controller is also proposed such that merits of the conventional hysteresis current controller can still be kept. Theoretical basis and some simulation and experimental results are presented to demonstrate the validity of the improved hysteresis current controller.

[516] S. Y. R. Hui, K. K. Fung, and C. Christopoulos, "Decoupled simulation of dc-linked power electronic systems using transmission-line links," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 85-91, 1994.

This paper describes the application of the transmission-line modeling (TLM) method to the decoupled simulation of d.c. linked power electronic systems. Stiff capacitively or inductively smoothed dc links in power electronic systems can be modeled as two-port transmission-line links using the TLM method. The TLM links enable the circuits connected by the links to be decoupled and simulated as individual circuits, resulting in smaller system matrices, possibility of parallel computation and reduction in computing time. Interaction between these linked circuits can be realised by exchanging the incident pulses at both ends of the transmission-line links. Computer simulations of an ac to dc converter used in a laboratory confirms the simplicity of the TLM decoupled simulation approach.

[517] R. Bonert and J. D. Lavers, "Simple starting scheme for a parallel resonance inverter for induction heating," IEEE Transactions on Power Electronics, vol. 9, no. 3, pp. 281-287, 1994.

A starting scheme for thyristor-based parallel resonant current source inverters, with particular reference to induction heating applications, is presented. The input stage to the dc-link is a three-phase phase controlled rectifier. It is shown that instead of using the usual startup circuits providing forced commutation, it is possible to start the system by using a single additional thyristor across the dc-link inductor, together with a special timed gating at the input and output converter. The scheme provides startup for a wide range of loads. The paper explains the principle starting concept and derives a simplified model to quantify the important parameters that govern the startup. The theoretical concept is verified by experimental data demonstrating the start of such an inverter.

[518] L. Salazar and G. Joos, "Pspice simulation of three-phase inverters by means of switching functions," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 35-42, 1994.

Static power converters can be analyzed by means of widely available circuit simulation software packages such as PSPICE. However, they are usually modeled as a set of real switches, which results in long execution times and possible convergence problems in the case of complex circuits. This paper proposes macromodels to simulate three-phase power converters on such packages. The proposed macromodels are based on converter switching functions rather than actual circuit configuration, and they are suited for steady state and large signal transient analysis at system level. In this approach, voltage source inverters (VSI), current source inverters (CSI), and controlled rectifiers (CR) are simulated as multiport networks avoiding the physical nonlinear micromodels of the power switches. Computer memory and the run-times required for the simulation are thereby minimized. Complete examples of VSI, CSI and CR, with different PWM techniques, are given with specific reference to the PSPICE software to illustrate the effectiveness of the proposed models.

[519] A. Lamantia, P. G. Maranesi, and L. Radrizzani, "Small-signal model of the cockcroft-walton voltage multiplier," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 18-25, 1994.

The description of the small-signal dynamics of the Cockcroft-Walton voltage multiplier is obtained through state-space modeling in the discrete time. Its small-signal equivalent circuit is a two-port linear network whose four transfer functions are given in the Z-transform. Main characteristics and general formulae of the multiplier with an arbitrary number of cells are derived. The expressions of cut-off frequency, gain and output impedance are given, and module and phase frequency responses are plotted.

[520] A. Brambilla and E. Dallago, "Analysis and design of snubber circuits for high-power gto dc-dc converters," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 7-17, 1994.

This paper presents the analysis and the design of snubber circuits for high power DC-DC converters realized with Gate Turn Off thyristors. These networks are fundamental for the safe operation of semiconductor devices but dissipate some energy. Means to minimize their losses are studied in this work. The snubber circuits described here are an evolution of the conventional C-snubber and L-snubber. The design of the snubbers is based upon circuits that permit the transfer of the trapped energy to the power source or to the load. Benefits, drawbacks and limits of each new proposed circuit are detailed and studied. Experimental results, obtained from a GTO laboratory prototype converter are reported.

[521] H. Shirahama, Y. Sakurai, Y. Matsuda, Y. Ishigaki, and K. Murai, "Instantaneous control method with a gto converter for active and reactive powers in superconducting magnetic energy storage," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 1-6, 1994.

A new type of GPG (gate pulse generator) is presented to give GTO converters quick response firing angle control and PWM control functions. Using the GPG, an instantaneous control method of active and reactive powers for an SMES (superconducting magnetic energy storage) employing one GTO converter is studied.

[522] J. S. Glaser and A. F. Witulski, "Output plane analysis of load-sharing in multiple-module converter systems," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 43-50, 1994.

This paper explores the origin of the dc current-sharing problem of parallel-converter systems and the dual problem of voltage sharing in series-converter systems. Both problems may be studied by examining the output plane (output current versus output voltage) of a particular converter. It is shown that strict current source behavior is unnecessary for good current sharing in parallel-converter systems. Furthermore, a broad class of converters whose output voltage is load-dependent, i.e., those that have a moderate value of output resistance, all exhibit good voltage- and current-sharing characteristics. Such converters are often suitable for a × b arrays of converters that can meet a large range of power-conversion requirements. The output planes of discontinuous mode PWM converters as well as conventional and clamped series resonant converters are examined in detail. A simple small-signal model of the modular converter system is developed. Experimental confirmation of load sharing and the small-signal model is given for the clamped series resonant converter and the series resonant converter for various configurations of four converters.

[523] M. Futami, T. Endoo, Y. Notohara, and T. Kitayama, "Digital automatic current control system based on an optimum assumed model," IEEE Transactions on Power Electronics, vol. 9, no. 1, pp. 51-55, 1994.

In this paper, a new ACR (automatic current regulator) scheme is introduced. It consists of a model closely resembling the motor and PWM inverter, an assumed rising pattern of the current, and a parameter estimation. Using the control scheme, the mean value of the motor current is kept at the reference current, and the transient current of the motor is kept equal to the rising pattern. For the disturbance, because of dc-line voltage change, the proportional path from the error to the duty cycle of the PWM signal stabilizes the ACR. This ACR scheme can be realized with a microcomputer.

[524] H. L. Liu and G. H. Cho, "Three-level space vector pwm in low index modulation region avoiding narrow pulse problem," IEEE Transactions on Power Electronics, vol. 9, no. 5, pp. 481-486, 1994.

In using GTO, a few hundreds micro seconds longer than specified pulse width must be guaranteed for safety for each device to commutate with its inherent gate current sequences. This paper describes the mechanism of generating undesirable narrow pulses in conventional three-level space vector PWM and suggests two new algorithms of space vector PWM using Non-Nearest three and four vectors in a control period to avoid such a narrow pulse problem. Experimental verifications for the suggested algorithms are also presented.

[525] T. Matsuo, V. Blasko, J. C. Moreira, and T. A. Lipo, "Field oriented control of induction machines employing rotor end ring current detection," IEEE Transactions on Power Electronics, vol. 9, no. 6, pp. 638-645, 1994.

The usual method of induction motor torque control uses the indirect field orientation principle in which the rotor speed is sensed and slip frequency is added to form the stator impressed frequency. Unfortunately, the rotor resistance varies as the motor heats up under load thereby changing the rotor time constant which has a deleterious effect on the torque response. In this paper two new field oriented control schemes are presented which employ rotor end ring current detection and thereby remove the dependence of the controller accuracy on temperature so that the controller is entirely independent of rotor time constant variations. The field orientation schemes do not require an incremental encoder for rotor position sensing. The motor torque can be accurately controlled even down to zero speed operation.

[526] M. Sakui and H. Fujita, "Analytical method for calculating harmonic currents of a three-phase diode-bridge rectifier with dc filter," IEEE Transactions on Power Electronics, vol. 9, no. 6, pp. 631-637, 1994.

Commonly, three-phase diode bridge rectifiers with an L-C filter at the dc side are often used to convert ac input into a dc voltage. It is well known that they generate large amounts of harmonic currents. This paper proposes an analytical method for calculating the harmonic currents for both the continuous and discontinuous current conductions. The equations for the harmonic currents are derived, taking into account the effects of the dc and ac side impedances. All the calculations are conducted only by algebraic calculation with high accuracy. The validity of the proposed method is demonstrated by comparison to the results of time simulation.

[527] M. S. Arefeen, M. Ehsani, and T. A. Lipo, "Sensorless position measurement in synchronous reluctance motor," IEEE Transactions on Power Electronics, vol. 9, no. 6, pp. 624-630, 1994.

A new discrete position sensor elimination technique for a sinusoidally wound synchronous reluctance motor drive is presented. The proposed technique determines the rotor position at zero crossing of the phase currents. The rotor position between the zero crossings is determined by applying extrapolation. The proposed technique works well at all speeds, including zero speed. This technique can be used in both vector controlled and conventional constant Volts/Hertz type of motor controllers.

[528] B. Choi, B. H. Cho, F. C. Lee, and R. B. Ridley, "Stacked power system: A new power conditioning architecture for mainframe computer systems," IEEE Transactions on Power Electronics, vol. 9, no. 6, pp. 616-623, 1994.

The stacked power system combines series and parallel connections of multimodule power supplies to produce several low voltage outputs at high current levels. The system could generate ultra low voltage outputs with higher efficiencies than conventional centralized or distributed approaches, using standard single-output converters. This paper presents the architecture of the stacked power system and establishes a design procedure for the system.

[529] F. Garofalo, P. Marino, S. Scala, and F. Vasca, "Control of dc-dc converters with linear optimal feedback and nonlinear feedforward," IEEE Transactions on Power Electronics, vol. 9, no. 6, pp. 607-615, 1994.

This paper describes a new control design procedure for PWM dc-dc converters. The control action has two components: a linear feedback, designed via LQ approach, and a nonlinear feedforward. The proposed control scheme guarantees excellent regulation of the output voltage, even in the presence of large variations of the input reference signal, as pointed out by numerous simulations carried out on different converter topologies. Good performances are also achievable when a suitably designed estimator is inserted into the control loop to reconstruct internal variables and input voltage disturbances from output voltage measurements.

[530] G. Hua, E. X. Yang, Y. Jiang, and F. C. Lee, "Novel zero-current-transition pwm converters," IEEE Transactions on Power Electronics, vol. 9, no. 6, pp. 601-606, 1994.

A new family of zero-current-transition (ZCT) pulse-width-modulated (PWM) converters is proposed. The new family of converters implements zero-current turn-off for power transistor(s) without increasing voltage/current stresses and operates at a fixed frequency. The proposed converters are deemed most suitable for high-power applications where the minority-carrier semiconductor devices (such as IGBT's, BJT's, and MCT's) are predominantly used as the power switches. Theoretical analysis is verified on a 100 kHz, 1 kW ZCT-PWM boost converter using an IGBT.

[531] H. Nakamura, Y. Murai, and T. A. Lipo, "Quasi current resonant dc link ac/ac converter," IEEE Transactions on Power Electronics, vol. 9, no. 6, pp. 594-600, 1994.

A new quasi current resonant dc link (QCRDCL) topology has been developed in this paper. Although prototype current resonant dc link topologies for ac/ac power conversion have had such problems as irregular high current peaks, uncontrollable pulse width, etc., this new topology enables the ac/ac conversion system to have the properties wherein the current peak is limited and the pulse width is adjustable. The system begins to assume an adjustable-width flat-topped current shape, whereby the system becomes particularly suitable for high power application. With control of the pulse width a very fine load current regulation can be obtained. In this system, an open loop PWM control has been adopted and almost the same quality of output waveforms as the conventional current source inverter has been achieved.

[532] A. Cavallini and G. C. Montanari, "Compensation strategies for shunt active-filter control," IEEE Transactions on Power Electronics, vol. 9, no. 6, pp. 587-593, 1994.

Compensation strategies for control of shunt active filters are compared in the paper. It is shown that the strategy based on unity-power factor control is appropriate when the supply voltage waveform of the plant where the active filter is connected shows significant distortion. As voltage distortion increases, this strategy provides compensated line current having lower harmonic distortion and RMS value with respect to the strategy generally used. This contributes to diminish the current and voltage distortion in networks. The unity-power factor compensation strategy conditions the current flowing in the plant where compensation is realized to fit the voltage waveform, thus reaching a unity power factor. Hence, the line current RMS value is minimum. The comparison of the strategies is performed by both Monte Carlo and ATP simulation.

[533] J. F. Chicharo and H. Wang, "Power system harmonic signal estimation and retrieval for active power filter applications," IEEE Transactions on Power Electronics, vol. 9, no. 6, pp. 580-586, 1994.

This paper presents a new adaptive Infinite Impulse Response (IIR) Line Enhancer (LE) comb filter configuration for the purpose of power system harmonic signal estimation and retrieval. The Approximate Maximum Likelihood (AML) algorithm is employed for the parameter update. The proposed solution is characterized by modest computational burden, effective tracking capabilities and provides the retrieved harmonic components with little or no distortion. The retrieved power system harmonics may be obtained on an individual basis or as a composite signal. Practical test results are included which show the performance achieved by the proposed technique.

[534] D. A. Torrey, "Project-oriented power electronics laboratory," IEEE Transactions on Power Electronics, vol. 9, no. 3, pp. 250-255, 1994.