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This paper proposes a methodology for developing integrated auxiliary soft-switching cells for power converter systems with two or more switching poles. The integrated cells obtained are a combination of cells from the same soft-switching technique or even of cells from different techniques, giving rise to hybrid cells. The resulting cells have fewer components, are lighter, and have a smaller volume than the conventional ones. Experimental results from a 1-kW power converter with two switching poles are presented to demonstrate the proposed methodology. Index Terms--Circuit synthesis, lossless circuits, switching circuits.

This paper proposes a novel synthesis methodology to generate integrated zero-voltage-transition (ZVT) topologies, as well as to systematize the topologies that are already known. An approach is presented to classify single-pole ZVT converters. This approach can be expanded to multipole systems, such as polyphase inverters and rectifiers, uninterruptible power supplies, and variable-speed drives. The connections among several presented topologies are easily seen by means of the general diagrams that are shown in this paper. Analysis and understanding of the advantages, disadvantages, merits, and limitations of each converter are made easier since these converters are obtained from a common approach that is presented in this paper. Index Terms--Circuit synthesis, lossless circuits, switching circuits.

This paper presents a detailed analysis of the impact of a hybrid multilevel modulation strategy on the harmonic content of the input currents and output voltages. Advantages and limitations of this modulation strategy are first discussed from the load point of view. This paper also proposes a new modulation strategy for hybrid multilevel inverters which can be used with asymmetrical multipulse connection of uncontrolled rectifiers to improve the input harmonic performance of adjustable-speed drives at every operating point. This new modulation strategy maintains the original capability to synthesize output voltages with reduced harmonic distortion and makes it possible to eliminate undesirable low-frequency harmonics from input currents in all operating ranges, even when the series-connected cells process distinct active power levels. Index Terms--Harmonic analysis, multilevel systems, multipulse converters.

The concept of hybrid multilevel converters has been generalized for different arrangements of direct-current voltage levels, modulation strategies, topologies of series-connected cells, and/or semiconductor technologies to optimize the power processing of the overall system. Therefore, a given number of levels can be synthesized by several multilevel configurations, significantly increasing flexibility and complexity in the design of hybrid multilevel converters. However, a generalized design methodology to define the main parameters of these topologies for distinct design criteria has not yet been presented. To overcome this lack, this paper presents a comparative analysis among various hybrid multilevel topologies, and it proposes some design considerations for distinct applications. Consequently, this paper constitutes a useful basis for defining an adequate hybrid arrangement for any application. Index Terms--High-power applications, multilevel systems.

This paper proposes a design criterion for calculating the resonant auxiliary elements of zero-voltage transition dc-dc pulsewidth-modulated (PWM) converters that use a dc auxiliary voltage source. The proposed criterion is based on stored energy in resonant auxiliary elements and takes into account the influence of the auxiliary voltage source value. Using this criterion, the reactive energy can be kept at a minimum level and a reduction of the auxiliary elements current ratings is achieved, which leads to lower conduction losses and improved converter efficiency. In addition, a reduction in size of auxiliary magnetic elements can be accomplished. To illustrate the usefulness of the proposed design criterion, the paper compares results obtained from the True-PWM Zero-Voltage Switching pole boost converter designed according to the proposed criterion, and from the original design guidelines. Experimental results show an efficiency gain of about 1% for a wide load range and 1.5% at full load. In addition, a reduction of about 52% in the auxiliary transformer volume for the implemented prototype was achieved, ensuring a reduction in overall converter size. Experimental results were obtained using a 1-kW 100-kHz laboratory prototype. Index Terms--DC-DC power conversion, pulsewidth-modulated (PWM) power converters, switching circuits.

This paper proposes an integrated zero voltage transition (ZVT) auxiliary commutation circuit applied to a universal input ac/dc system with a bidirectional converter for dc bus and battery bank interface. With the bidirectional converter it is possible to reduce the cost of the battery bank and virtually eliminate both low and high frequency current ripple in the batteries. An integrated ZVT auxiliary commutation circuit has been included to the system to achieve ZVT commutation at the main switches in all operation modes. In addition, this auxiliary commutation circuit controls the di/dt of the resonant process, allowing the utilization of slow diodes [intrinsic diodes of metal oxide semiconductor field effect transistors (MOSFETs)] in the bidirectional converter and, therefore, reducing the overall system cost. Integrated commutation circuit is based on a new concept in which the energy involved in one or more commutation processes is utilized to assist another commutation processes. Moreover, a control system has been developed and analyzed for the correct operation of the proposed system. Experimental results based on a 580-W prototype are presented to demonstrate the good performance of the proposed system. Index Terms--Soft-switching, uninterruptible power supply (UPS), zero voltage transition (ZVT).

This paper presents a universal auxiliary commutation cell for pulse-width modulated (PWM) inverters termed zero current and zero voltage transition (ZCZVT) commutation cell. It provides zero current and zero voltage commutation, simultaneously, during main power devices turn-on and turn-off, with controlled di/dt and dv/dt. As a result, commutations of the main power devices occur without any losses. This unique characteristic is not achieved by any other soft-switching commutation cell for inverters hitherto presented in the literature, making it a strong candidate for use in low-power (MOSFET), medium-power (IGBT) or high-power applications (GTO, thyristor). Furthermore, reverse recovery losses of main diodes are minimized and auxiliary switches commutate at zero current. To demonstrate the operation of the proposed universal auxiliary commutation cell, a ZCZVT PWM Full-Bridge inverter is analyzed. To evaluate the operation of the auxiliary circuit in different conditions, prototypes with both IGBTs and MOSFETs for different output powers levels were implemented and their performances compared. Experimental results confirm that there is no overlap between main switch current and voltage, and that waveform ringing is practically eliminated. Index Terms--Inverters, soft-transition, ZCZVT.

This paper presents a new isolated dc-dc zero-voltage-switching (ZVS) converter, which is composed of two half-bridge converters associated in series operating at constant frequency. The converter can be seen as an alternative to the ZVS-phase-shift full-bridge dc-dc converter for high-voltage applications. The paper proposes a new command strategy, named interleaved phase shift, which allows equalization of the input capacitor voltage, where each capacitor shares one-quarter of the total input voltage. Due to phase-shift modulation, the current is equally shared among main switches, reducing the converter conduction losses, when compared with conventional pulsewidth modulation. Furthermore, the input capacitors voltage oscillations are reduced due to load variations, as well as due to input dc-bus 120-Hz ripple. Just as with a ZVS-phase-shift full-bridge converter, the proposed converter achieves ZVS in a wide load range, as a function of the transformer leakage inductance. The paper describes the analysis, operating principles, and design procedure for the proposed converter. Experimental results from a 1.5-kW prototype converter operating at 100 kHz with isolated 60-V/25-A output are presented to validate the theoretical analysis and to demonstrate the performance of the proposed converter. Index Terms--DC-DC converters, multilevel converters, power supply, soft switching.

This paper presents a model reference controller with a repetitive control action for uninterruptible power supply (UPS) applications. The model reference controller modifies the structure of the plant so that the closed-loop transfer function is equal to a chosen reference model transfer function, whereas the repetitive control action minimizes periodic distortions caused by unknown periodic disturbances. Design procedure and stability analysis of the control scheme are discussed. Simulation and experimental results for a single-phase PWM inverter (110 [V.sub.RMS], 1 kVA) controlled by a low cost microcontroller are presented to verify the performance of the proposed control approach under different load conditions. Index Terms--Digital control, uninterruptible power supplies, voltage-source PWM inverters.

This paper presents a comparison among digital control techniques with repetitive integral action applied to voltage-source PWM inverters. As a result of the repetitive integral action, these digital control schemes can reduce steady-state errors and distortions caused by unknown periodic disturbances, which usually result from the input source and output load. Moreover, these digital control schemes measure only the output voltage, decreasing the amount of sensors and the overall system cost. The control laws, stability analysis, common and distinguishing features of these control algorithms are discussed. Experimental results from a PWM inverter (110 [V.sub.RMS], 1 kVA) controlled by a low cost microcontroller are presented to demonstrate the control techniques performance under different load conditions, output filters and command strategies. Index Terms--Digital control, repetitive control, uninterruptible power supplies, voltage-source PWM inverters.

This paper investigates a power-factor-corrector (PFC) circuit based on interleaved boost converters in critical conduction mode (C-DCM) with a zero current transition (ZCT) circuit. By using the interleaved converters technique, the input current ripple is minimized, and due to the operation in C-DCM, the main switches turn-on occurs naturally under zero current and the reverse recovery losses of the diodes are minimized. The use of auxiliary commutation circuits provides ZCT at main switches turn-off, minimizing the related turn-off losses. The command circuit of the converters has been implemented by using a single erasable programmable logic device (EPLD) EPM7128SLC84-15. Operating principles, theoretical analysis, design guidelines and a design example are described and verified experimentally by a 1.2 kW prototype. Finally, the measured losses in the PFC interleaved boost converters with and without the proposed ZCT commutation cell, as well as a previously published ZCT cell are presented and discussed. Index Terms--Power-factor-corrector, soft-switching, ZCT.

This paper presents the analysis and design of a new low-loss auxiliary circuit for three-level pulsewidth-modulation single-phase full-bridge inverters which achieve soft switching at all semiconductor devices. The active auxiliary commutation circuit (AACC) is composed of an LC circuit and two bidirectional switches, where one auxiliary switch commutates under zero-voltage switching condition and the other under zero-current switching condition. The AACC dispenses with the use of auxiliary voltage sources. Low reactive energy is added to the converter, resulting in low rms current stresses at the main switches and, consequently, higher efficiency is achieved. Auxiliary circuit design procedures and experimental results are presented to prove the operation principle. Index Terms--Pulsewidth modulation, soft switching, three-level inverter, zero-voltage switching.

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.