Improved Switching Performance of 3.3kV SiC MOSFETs using Synchronous Rectification in A Voltage Source Inverter

In this paper, switching performance of a 3.3kV, 40A SiC MOSFET has been investigated. Switching losses of the SiC MOSFET were obtained at various device case temperatures between 25°C and 1250C in a low-inductance double pulse test (DPT) setup for three different test cases to predict the SiC MOSFET's performance in a voltage source inverter (VSI). In case I, the switching transitions occurred between the device under test (DUT) MOSFET and the body diode of another SiC MOSFET (same model). In case II, a SiC Schottky diode is connected across the top SiC MOSFET to block the influence of body diode. In case III, synchronous rectification is considered with a dead-time of 120ns (no Schottky diode). It has been observed that the SiC MOSFET incurred high turn ON loss due to the reverse recovery of freewheeling body diode. Paralleling of SiC Schottky diode to block the influence of body diode has been effective only for temperatures above 750C. Moreover, additional Schottky diodes require larger chip-area which results in reduced power density and increased component costs. It has been noticed that the MOSFET incurred minimum turn ON loss for the whole temperature range (250C to 1250C) when synchronous rectification was used with a dead-time of 120 ns (case III). As the freewheeling body diode conducted current only during the small dead-time period, reverse recovery was significantly reduced. Hence, synchronous operation proves to be the better solution compared to the paralleling of Schottky diode in high-frequency SiC voltage source inverters.