Analysis of the Zero Overvoltage Switching Phenomenon

Abstract

In common understanding, the fast switching speed of wide-bandgap devices leads to high overvoltage and oscillations, if no countermeasures are taken. Those countermeasures were introduced in the past, and include methods such as build-in gate resistors or low-inductive power modules. There is, however, a physical limit for reducing the parasitic inductance of the commutation cell. This is one of the reasons why the full potential of wide-bandgap devices cannot be entirely utilized. In contrast, the Zero Overvoltage Switching (ZOS) phenomenon can be used to theoretically unleash unlimited switching speed with no switching losses and voltage overshoots. This method triggers the inherent parasitic oscillating elements of a commutation cell to perform an ideal current commutation. This article investigates the physical effects and usage of this technology in real-world applications. The model of an ideal commutation cell is adapted to reality by introducing damping factors as well as the nonlinear behaviour of the parasitic capacitances. An extended ZOS area is presented, including the parasitic capacitances of two wide-bandgap devices. It allows today’s silicon carbide power modules to make use of the ZOS technology and perform at different power levels. Measurements with a commercially available power module were taken to verify the theoretical analysis and the derived equations.