Highly compact isolated gate driver with ultrafast overcurrent protection for 10 kV SiC MOSFETs

Silicon Carbide (SiC) semiconductor technology offers the possibility to manufacture power devices with un-precedented blocking voltages in the range of 10...15 kV and superior switching characteristics, enabling switching frequencies beyond 100 kHz. To drive these 10 kV SiC devices, the power supply and the gate signal of the (high-side) gate driver require an appropriate galvanic isolation featuring a low coupling ca-pacitance and a high du/dt ruggedness. Since at the moment no commercially available gate drivers for these specifications exist, a customized isolated gate driver is developed, which, in order to simplify the use of the high-voltage SiC devices, is intended to be integrated into a future intelligent MV SiC module. For this purpose, a highly compact isolated gate driver with an isolation voltage rating of 20 kV is implemented and tested. The realized isolation transformer of the isolated power supply shows a volume of only 3.1 cm3 and a coupling capacitance of only 2.6 pF, and has been successfully tested at 20 kV DC. Furthermore, an ultrafast overcurrent protection (OCP) circuit is implemented to protect the expensive SiC modules from destruction due to overcurrents, which e.g. could result from false turn-on of both transistors of a bridge-leg or from short circuits of the load. The OCP circuit reacts within 22 ns to a fault and measurements prove that it can successfully clear both, a hard switching fault (HSF) and even a flashover fault (FOF), where one of the two switches of a bridge-leg configuration is subject to a flashover, in less than 200 ns for a DC-link voltage of 7 kV.