Analytical Method for RC Snubber Optimization Design to Eliminate Switching Oscillations of SiC MOSFET

The switching oscillations caused by the high-speed switching and low-damping characteristics of SiC mosfet seriously deteriorate its high-reliability applications. By viewing from the terminals of both SiC mosfet and diode for the turn- on and turn- off oscillation not only the two-port networks be formed to carry out more accurate analysis about the system characteristics but also the characteristic equations of the system can be deduced, thereby reliably guiding the RC snubber design. Since the oscillation is essentially caused by the imaginary part of poles, with the assistance of the two-port networks, an optimized design method of an RC snubber circuit is developed by the way of actively assigning poles. Different from existing analytical techniques, no necessity is needed to reduce the order of characteristic equations to yield the mathematical expressions of RC snubbers. Instead, RC snubber regions where oscillations can be completely suppressed are determined directly by an exhaustion method. An overlapping area is found, which means that both the turn- on and turn- off oscillation can be eliminated simultaneously by the same snubber circuit. Moreover, the related discussions about existence conditions of the snubber region, sensitivity to parameters, and the limitation in choosing RC are illustrated in detail. Finally, standard double-pulse tests are conducted on both the LTspice simulation and the laboratory experiment to verify the effectiveness of the analysis and proposed method.