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.

Fundamental Modeling of the Switching Transition in High-Speed Power Electronics

“…Specifically, it is to fundamentally understand how the circuit parameters and switching speed translate to the overshoot. These overshoot results of Fast-Mode are expected and are also experimentally verified in both [11] and [12]. This…”

“…4 shows the transition period is very small, with no overshoot and ringing, contrary to the expected results. These results were experimentally verified in [11] and [12].…”

“…The value of 𝑛 can be any integer larger than one and indicates the optimized point of operation will occur again when one of the variables changes. This equation is similar to those presented in [11] and [12], and when this equation is applied to the parameters of the overshoot plot in Fig. 10 above, with the choice of inductance as the variable, the following plot of Overshoot vs Switching speed can be seen in Fig.…”

“…This hurdle can be overcome by widening the area of operation or creating multiple areas of operation, and methods to achieve this are discussed in this section. The widening of the area of operation is also going to be the main research direction in Fast-Mode switching research and is also the main goal of [11] and [12].…”

“…This was mentioned in [12], which discusses how the presence of the 𝑛 value creates more than one optimisation point.…”