T35.2 - Forward Recovery and its Mitigation in Hybrid Si/SiC-Based DC–AC Converters

The ongoing progress in the field of wide bandgap (WBG) devices enables new topologies and unmatched power density in high-power dc–ac converters. However, the still high cost of WBG devices, such as silicon carbide (SiC) MOSFETs, continues to hinder their widespread adoption in commercial converters. To address this challenge, emerging hybrid topologies combine fast-switching SiC MOSFETs with Si IGBTs operating at the fundamental frequency, achieving an optimal balance between cost and performance. In such topologies, the rapid switching of SiC devices induces high current slew-rates, which trigger forward recovery effects in the IGBTs. This phenomenon leads to additional losses in these bipolar devices and generates transient overvoltages, compromising the converter’s reliability. This article investigates the forward recovery behavior of different IGBT technologies and explores the mitigation by introducing a snubber capacitor to decouple the different stages of the topology. The results demonstrate the effectiveness of this approach in mitigating the detrimental impacts of forward recovery in hybrid dc–ac converters.