New Three-Level Soft Turn-off T-type NPC Inverter

This paper presents research results of the novel three-level T-type neutral point clamped inverter (T-NPC) with an active auxiliary switching circuits (AASC) for soft turn-off operation. Application of the AASC allows for significant losses reduction in high voltage IGBT switches. It improves the turnoff process where faster collector current decrease and slower collector-emitter voltage rise is achieved. The presented concept is the novel solution which allows for substantial optimization of volume of auxiliary resonant chokes in relation to the established soft-switching concept. In the proposed solution the resonant chokes are used for charging of auxiliary snubber capacitors but do not conduct the load current. The paper presents the basic concept of the inverter with the AASC, the mechanism of losses reduction and the concept of switching. The AASC converter can operate with the classic phase disposition (PD) PWM. The presented concept of the inverter paper is verified by simulations results.