Effect of Parameters Spread on the Performance of SiC Power Modules: Derating Rules and Robustness Issues

In this dissertation, the criticalities involved in the parallel connection of SiC MOSFETs are analyzed. The first tool allowing this study is an inhouse developed compact model for SiC MOSFETs capable of running fully-coupled electrothermal simulation if connected to an appropriate equivalent thermal network. The model is verified over a selection of SiC MOSFETs covering the main voltage classes currently available on the market (i.e., 1.2, 1.7 and, 3.3 kV). The impact of relevant device and circuit parameters variability on parallel-connected SiC MOSFETs is evaluated by statistical means. This analysis lays the foundations for the development of a guideline for the identification of allowable parameters spread ensuring the safe operation of the parallel array. The guideline is derived from a procedure relying on the execution of multiple Monte Carlo electrothermal simulations and on the approximation of the thermal problem to a 1-D equivalent. Eventually, an efficient and versatile strategy for fast and accurate dynamic electrothermal simulations is used for modelling virtual prototypes of multichip power modules. The resulting virtual prototypes are simulated during their operation in complex switching converters and allow to identify critical temperature gradients resulting from mismatched characteristics of the devices. The significance of this finding lies in the fact that overheating of a single device, or a subset of them, could undermine the long-term reliability of the power module but cannot be easily identified by the system-level electrical behavior of the converter.