Conditions Limiting the Formation of the ZVZCT Switching in SAZZ Converter

The paper reports on formation of soft switching conditions in SAZZ converter topology. Abbreviation SAZZ represents snubber assisted zero voltage and zero current transition converter. In [2,3,4,5] high efficiency around 98% was reported for 100 kHz and 50 kHz converter with output power of 8 kW and 25 kW respectively. However, extreme changes of duty ratio could result in loss of soft switching. For the boost operation of SAZZ chopper circuit, when the output to input voltage ratio decreases below 2, the partial hard switching appears. Similarly for the buck operation, when the output to input voltage ratio decreases below 1/2, the partial hard switching appears. The theoretical analysis and simulation studies of SAZZ soft switching range are presented in this paper. The analysis is supported by experiments on 100 kHz- 8 kW SAZZ converter prototype.