Soft-switching techniques can significantly reduce the switching loss and switching stresses of the power semiconductor devices in a power converter. This work presents several soft-switching topologies for high power PWM converters. These new topologies achieve soft-switching functions with minimum increase of device voltage/current stresses and converter circulating energy, and thus have advantages over conventional techniques in efficiency, power density, reliability, and cost of power converters.

The improved zero-current transition (ZCT) converters achieve zero-current switching at both turn-on and turn-off for all main switches and auxiliary switches. These converters significantly reduce the switching loss and stress of the power semiconductor devices, while have a voltage/current stress and circulating energy similar to a PWM converter’s. The analysis, design, and experimental verification are presented.

The three-phase zero-voltage transition (ZVT) boost rectifiers/voltage source inverters are developed with simple auxiliary circuits. Unlike most existing three-phase soft-switching techniques, these new topologies achieve soft-switching functions without overcharging the resonant inductors, and realize the benefits of soft-switching operation with minimum extra main switch turn-offs and fixed auxiliary circuit control timing. The operation principles of the developed techniques are experimentally verified, and their efficiency performances are evaluated with experiments and computer simulation.

The three-phase ZVT buck rectifier topologies developed in this work achieves zero-voltage turn-on for all main switches with an optimum modulation schemes and simple auxiliary circuits. The auxiliary circuits, which are connected directly to each main switch, can also absorb the parasitic resonance of the bridge arms, and keep the voltage stress of the power devices at the minimum. The analysis and simulation results are presented to verify the converter operation.

New ZVT dc-link schemes for three-phase ac-dc-ac converters are investigated. With coordinated control of the ac-dc converter and the dc-ac converter, a set of simple auxiliary circuit can provide soft-switching function for all switches in both the ac-dc converter and the dc-ac converter. The power loss in the auxiliary circuit is also significantly lower than existing dc-link soft-switching schemes. Simulation with experimentally obtained device switching loss data proves that significant efficiency improvement can be achieved with the new ZVT dc-link techniques.

New ZVT and ZCT techniques for three-level converters are also developed. The auxiliary circuits are not in the main power path, and allow the converters to be controlled with optimum PWM schemes. Analysis and simulation results are presented to demonstrate the operation principles and advantages of soft switching in three-level converters.