A passive coupled-inductor flying-capacitor lossless snubber circuit for plasma cutting power supply

Plasma cutting power supplies in the power range 20 kW and above commonly use the hard-switched buck converter topology. This topology is simple and efficient when compared with SCR based methods. In addition, circuit reliability is achieved by using current controlled PWM technique at a typical switching frequency of 15 kHz. It is however estimated that device switching losses make up about two-thirds of the total switch power loss. This significantly influences device cooling requirements and overall system efficiency. This paper presents a passive lossless snubber circuit that reduces the converter switching losses. It is based on a coupled inductor with flying-capacitor network and is an improvement over a turn-on coupled inductor snubber circuit proposed in H. Levy, et al. (1997) in that it reduces switch turn-off losses as well. The circuit operation is analyzed in the paper and verified by means of experiment, results of which are presented