Comparison of SiC Synchronous Rectification and Schottky Diode in Voltage Source Inverters

SiC Schottky diode has been widely used as the antiparallel freewheeling diode in the IGBT or SiC MOSFET based power inverter applications. However, these solutions have drawbacks of large switching loss of the IGBT or costly SiC MOSFET. To achieve the cost-effectiveness and higher conversion efficiency, we propose a low power SiC MOSFET with the synchronous rectifier (SR) operation in replacement of the SiC Schottky diode in an IGBT based voltage source inverter (VSI). The SiC MOSFET works as an auxiliary switch of the main IGBT, greatly reducing the forward conduction loss. Its SR operates in the reverse conduction, greatly reducing the conduction loss, especially at light load. And it also enables the zero voltage switching operation of the IGBT, greatly reducing the switching loss of the IGBT. The conduction and switching characteristics of the SiC Schottky diode and SR are measured and compared. Then a 4kW single-phase VSI prototype based on these two solutions are investigated. Experimental results show that the SiC SR operation can achieve 28% smaller total power losses, 0.9% higher conversion efficiency and 50°C lower case temperature of power switches than the SiC Schottky diode in VSI.