Investigation on Optimal Switching Oscillation Suppression for SiC MOSFET by Inductively Coupled Damping

SiC MOSFET has been revolutionizing power electronics but producing more severe switching oscillation due to its inherent faster switching speed and lower damping characteristics. The inductively coupled damping approach is promising since no additional circuit element is inserted into the power processing loop. Thus, reliability of this inductively coupled fashion is higher compared to other existing snubbers. However, prior-art analytical design techniques are mainly based on scrutinizing the peak impedance and only discussed under a certain specific coupling, which limited its suppression effect. In this article, by viewing from the terminals of both upper and lower SiC MOSFETs in a half-leg circuit, two-port networks are linearized from switching oscillation and developed to deduce the exact characteristic equations. Then, the optimal snubber configuration along with two key parameters, i.e., the inductance factor and the secondary resistance, are determined via the root locus method. It is revealed that the damping effect of RL in the strong coupling region is even better than that of the secondary RLC resonator. What is more, applying the coupled RL damping circuit could not only remarkably dampen the switching oscillations, but also greatly lower switching losses. Finally, discussion on selecting the optimal snubber parameters is illustrated in detail.