Research On Three Level Soft-Switching Converter

In the information age, higher and more requirements for power conversion technology are put forward with the development of every profession, such as improvement of efficiency, reducing the volume and the harmonic pollution, saving the energy, reliable operation, etc.However,there is no end to the demand for a high-power high performance power supply,then three-level converters are presented and researched widely in power electronics applications,especially for the high-power field.The main purpose of proposed three-level converter is to reduce voltage stress across the power switches.With the development of soft switching technology, the problem that how to combine three-level converter with soft-switching has become a hotspot of study.First of all, the processing and structures of half-bridge three level converter are introduced and the conventional Phase-Shifted Zero-Voltage Switching PWM Three-Level converter is studied specically which integrates the advantages of resonant converters and PWM converters. Although the ZVS for the power switches can be realized, some disadvantages such as hard for relizing soft switching of lag arm, circulating current loss,duty-cycle loss and the output rectifier diodes’voltage spike are brought at the same time, which boosted the development of three level converters. Gradually, the ZVS three level converter with auxiliary circuit is changed to ZVZCS three level converter. And a novel ZVZCS three level converter is proposed in the paper.Then the novel phase shifted ZVZCS PWM three-level converter which consists of a simple auxiliary circuit in the secondary winding is discussed. It inherits all advantages of three level converters, whose voltage stress for each switch is reduced to half of input voltage too, which makes it very suitable for high input voltage applications.A wide range of loads’ soft-switching for all switches can be achieved by using the tapped-inductor type smoothing filter, shunt capacitors and transformer parasitic inductors.This converter can reduce the voltage of the switches, current peak and ciculating current loss. The operation principle of the new type converter according to the different equivalent circuits is analyzed.And its soft switching implementation conditions,output voltage characteristic, curren stress of switches and circulating current loss, the analysis of the circuit and parameter design method are presented.Finally, the operation principles, feasibility of novel converter and correctness for theoretical analysis are validated by the computer simulation analyze.