Practical Insulation Testing of 10 kV SiC MOSFET Modules

This study aims to develop an additional screening process to select reliable power modules, as multiple modules experienced insulation failure during previous converter qualification steps despite passing static device characterization and the manufacturer’s end-of-line (EOL) baseplate isolation and partial discharge (PD) testing. DC and PWM soak tests were conducted where the modules were left to dwell under the specified voltage excitation. The testing procedure involved applying the excitation in timed increments of approximately 1-hour, then measuring the partial discharge inception voltage (PDIV) after each step until the final target soaking voltage was reached or the PDIV fell below the operational threshold. Out of 24 half-bridge modules tested, 87% passed dc soaking test, while only 44% passed PWM soaking. The modules that failed under PWM soak also failed at a much lower voltage than those that failed under dc soak; indicating that PWM soak tests have greater stress on module insulation. This highlights the importance of using various stress tests to assess insulation health and integrity.