A 99% efficiency SiC three-phase inverter using synchronous rectification

The reactive power in power converter with inductive load (motor drive e.g.) requires a current commutation path for the freewheeling current. Due to the high voltage drop of body diode of SiC MOSFET, a SiC Schottky diode is normally recommended as the anti-parallel freewheeling diode for SiC MOSFET to suppress the conduction of body diode. However, since the MOSFET can work as synchronous rectifier, the freewheeling diode only conducts during the dead time, leading to a low utilization rate of device. In this work, the three-phase SiC inverter using synchronous rectification is investigated. The analytical model for inverter power loss with and without freewheeling diode is built. Based on the switching characterization, the inverter with synchronous rectification permits a surprising higher efficiency than that with freewheeling diode due to the reduced current overshoot at turn-on. And a 5 kW prototype of three-phase inverter is developed, which shows a 99% high efficiency at the switching frequency of 40 kHz. This work confirms the possibility to remove the freewheeling diode in SiC inverter without degrading the efficiency.