A Novel ZCS PWM Half- bridge Converter

¡¡¡¡Introduction

¡¡¡¡In order to improve the whole efficiency of the electronic equipment, the search for more efficient soft switching technique has been developed. For switch such as IGBT,the zero- current switching(ZCS) and zero-current transition(ZCT)technology have been frequently used, because this method can reduce the current rapidly when IGBT turns off, therefore reducing the energy loss caused by the tail current [1][2][3][4][5].

¡¡¡¡But the zero-current switching circuit that mostly used is not input-out-isolated, so the application in the practice has not been generalized. This paper proposed the ZCS technique realized by the halfª² bridge converter, both the main switch and auxiliary switch in the topology work in softª² switching state, the turn-on current stress and turn-off voltage stress is small.

¡¡¡¡1 Operational Principles

¡¡¡¡Fig.1 shows the circuit diagram of the half-bridge converter. In the schematic, Lr1 to Lr4 are resonant inductors, the Cr is resonant capacitor, S1 and S2 are main switches, S3 and S4 are auxiliary switches, D1 to D4 are anti-parallel diodes in the switches, Cs1 to Cs4 are snubber-capacities. The circuit is the conventional halfª² bridge topology incorporating the auxiliary resonant tank that composed of switches S3 and S4. The zero current switching state can be obtained by controlling the work sequence of the switches. Fig.2 is the theoretical waveforms when the converter in steady-state operation.