Modular design of soft-switching circuits for two-level and three-level inverters

This paper presents a negative-bus auxiliary resonant circuit (NBARC) and novel mirror symmetrical pair of resonant link modules for soft commutation of two-level and three-level inverters. The NBARC topology reduces the power device counts and requires low device power ratings. While the basic NBARC resonant circuit is conceived and analyzed for zero-voltage switching (ZVS) of two-level inverters, the topology and modular design approach are extended to form a pinched-link resonant stage of ZVS for three-level inverters using mirror-symmetrical pair of resonant modules. The circuit is also designed as an optional module that can be attached to a standard inverter bridge and converted into a soft-switched inverter. Experimental results verify our circuit analysis and implementation.