Design optimisation of a resonant turn-off snubber for high-power converters

An active resonant turn-off snubber suited for high-power IGBT converters is presented. The main feature of the snubber is that the maximum current rating of the auxiliary switching devices is small compared with that of the main switches. The basic operation of the snubber is described. This is followed by a detailed analysis of the losses in the circuit, which gives rise to an optimum snubber design procedure. An experimental version of the snubber is evaluated on an IGBT phase-arm, and detailed measurements of the efficiency of the converter are taken. The experimental results are in close agreement with the theoretical predictions.