Design Challenges of SiC Devices for Low- and Medium-Voltage DC-DC Converters

Silicon carbide (SiC) devices are considered as key enablers for the development of highly efficient and compact dc-dc converters for low- and medium-voltage applications. Besides their high temperature capability and low conduction losses, they provide superior switching characteristics.This paper emphasizes design challenges of SiC devices in the low- and medium-voltage range arising from their fast switching speeds. First, detailed measurement results on the switching characteristics of 1200 V SiC devices and different leakage inductances are presented. The results are assessed with regard to the switching losses as well as the transient voltage and current overshoots. The impact on the switching behavior as function of leakage inductances is shown. The leakage inductances also influence the resonance frequency of the power module and dc-dc converters. This is a crucial design aspect to determine the size of the EMI filters. Its significance is demonstrated based on an 800 V dc-dc converter using commercially available SiC MOSFETs. Furthermore, zero-voltage switching is emphasized to reduce the impact of the module parasitic elements on the switching behavior. The performance of 10 kV SiC MOSFETs in a medium-voltage dc-dc converter shows, however, that a significant amount of commutation energy is required to ensure a successful soft-switching transition.