Current fed inverter bridge with lossless snubbers

Abstract

A DC-to-AC inverter includes a switched bridge circuit. The bridge is energized by a source of substantially constant direct current. In order to reduce stress on the switches of the bridge, periods of conductivity of the switches of the bridge are overlapped, so that all the legs of the bridge are conductive simultaneously in two operating intervals out of a recurrent operating sequence of four operating intervals. Each switch is associated with a snubber circuit including a snubber capacitor which bypasses or absorbs switch current during turn-off. The charge retained on the snubber capacitor after complete turn-off of the associated switch represents energy which can be reused. The capacitor must be discharged in readiness for the next turn-off of the associated switch. An energy recovery circuit associated with each snubber includes a transformer, the primary of which is coupled to the associated snubber capacitor for receiving a current pulse at a time near the beginning of one of the four intervals of the recurrent operating sequence. A secondary of the transformer of each energy recovery circuit is coupled to the energizing source for returning energy to the source while discharging the associated snubber capacitor.