ZVS PWM buck-boost converter applied to regenerate the energy of a three level NPC voltage-fed inverter with modified Undeland snubber

This paper analyses the utilization of an energy regeneration circuit in a three-level NPC (Neutral-Point Clamped) voltage-fed inverter using a modified Undeland snubber. The regeneration circuit uses a QSC (Quasi-Square wave Converter) ZVS (Zero Voltage Switching) dc-dc auxiliary converter to restore the energy from the snubber capacitor to the dc bus. The regenerative circuit uses a single active switch and operates independently of the inverter. Operation stages, theoretical waveforms and a design methodology are presented. Experimental results of a 1.5 kVA prototype are included to validate the proposed topology.