Experimental Investigation of the Impact of Soft Switching on Capacitive Bearing Currents in SiC-Based Motor Drives

In fast switching SiC-based frequency converters, the emerge of capacitive dv/dt bearing currents becomes increasingly relevant and is the main subject of this study. Based on experimental investigation, we observed a significant reduction in the occurrence of capacitive dv/dt bearing currents during soft switching events. In addition, the slew rate of the SiC MOSFETs show a massive impact on the overall height of the capacitive bearing currents. It is shown that the effect of soft switching has an impact on bearing currents, caused by the gradient of the common-mode voltage, regardless whether the bearing behaves capacitive or resistive. The purpose of this work is to improve the understanding of the interaction between the bearing currents caused by common-mode voltage gradients and the switching behavior of the frequency converter, with a focus on soft switching.