A Medium Power SiC Module with Integrated Active Snubber for Lowest Switching Losses

Better EMI performance and lower switching losses are important goals in power electronics. Since several years, wide-bandgap materials are subject of research, providing faster switching speeds and thus lower switching losses. However, fast transistors tend to oscillate due to stray inductance and parasitic capacitances. Furthermore, a high stray inductance leads to a high voltage overshoot at turn-off. For those reasons, a small stray inductance is essential for low EMI and low switching losses. A major difficulty during the development of a power electronic system is that the stray inductance is distributed over several parts, e.g. the DC-link capacitor, the connection, and the power module. Thus, achieving a low stray inductance is challenging. To alleviate that is the use of a snubber circuit, which, however, may lead to even higher overall losses. In this paper, a medium power SiC-MOSFET module is presented with an integrated active snubber that makes use of the energy in the stray inductance. It is compared with two other topologies, a standard halfbridge and a halfbridge with integrated DC snubber. The three topologies are tested in identical setups for hard-switching operation at 600V and 350A, all with similar DBC layout. It is shown that the voltage overshoot, the tendency to oscillate, and the system losses are strongly decreased due to the active snubber.