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This paper presents a novel active snubber recovery circuit for series-connected insulated gate bipolar transistors (IGBTs). The proposed technique allows turnon and turnoff switching of the series IGBTs to be controlled and balanced through conventional snubber effects, but the configuration includes active circuitry to recover into the dc supply, the stored snubber energy. Detailed waveform analysis and associated mathematical equations are presented, supported by PSpice simulations. The proposed technique is practically demonstrated, at a scaled power level, on a single IGBT to illustrate the control concept and on three series-connected IGBTs to demonstrate dynamic voltage sharing.
Date of Publication: July 2011