A Floating Voltage Source-Based Turn-Off Snubber for a Nonisolated Multilevel SiC DC-DC Converter

This article presents a turn-OFF snubber for a high-power, nonisolated, multilevel dc-dc converter (MLC) implemented with SiC MOSFETs. Although SiC devices are known to reduce switching losses, a snubber is essential to mitigate the high
dv/dt
ratio on the switch’s drain–source voltage, which results from the surge in current when the SiC switch is turned off. This work proposes a floating-voltage source (FVS)-based snubber, presenting a single-circuit solution that provides soft turn-OFF (ringing suppression) capabilities for multiple power switches in MLC. Moreover, it ensures that this soft turn-OFF feature is consistently effective across all duty-cycle (
D
) ratios of the MLC without any constraint. This work also presents two approaches for realizing the FVS-based snubber: dissipative and energy-regenerative methods. In this article, a prototype of a 7-kW three-level flying- capacitor buck (TLFCB) converter with a 537 V
_DC
input is developed. This prototype successfully demonstrates the effectiveness of the proposed snubber across
D
ranging from 0.2 to 0.8.