Resonant DC Link Three-level Soft-switching Inverter With Symmetrical Auxiliary Circuits

A resonant DC link three-level soft-switching inverter with symmetrical auxiliary circuits was proposed to reduce switching loss in the three-level inverter under high switching frequency. Symmetrical auxiliary circuits were arranged in the DC link of three-level inverter. The voltage across resonant capacitors between DC buses decreased to zero periodically via the resonation of auxiliary circuits. Main switching devices in the three-level inverter were operated when the voltage across resonant capacitors between DC buses was zero to realize zero-voltage switching. The operation principle of the soft-switching inverter was analyzed in detail on the basis of equivalent circuits at different operation modes. A 3 kW laboratory prototype of resonant DC link three-phase three-level soft-switching inverter had been built. Experimental results were demonstrated to confirm validity of soft-switching and improve efficiency compared with hard-switching inverters. Therefore, the proposed topology with engineering practicability in the paper can effectively reduce switching loss.