Series Connection of SiC MOSFETs with Hybrid Active and Passive Clamping for Solid State Transformer Applications

摘要

This paper presents a novel hybrid active and passive clamping technique for series-connected SiC MOSFETs with simple circuit structure and minimized power loss. Firstly, a dedicated switching pattern with predefined dead-time is proposed to keep the direction of current through flying capacitor unchanged under all conditions. Secondly, only single passive clamping device is in parallel connection with a small capacitor to clamp the voltages across all four SiC MOSFETs in a bridge leg within a few nanoseconds during high-speed dynamic switching transition of turn-on and turn-off. Then, the technology is extended to series-connection of n pieces of SiC MOSFETs in series per position in bridge structure using (n-1) clamping devices and capacitors. The hybrid clamping technique could be applied in any topologies including AC-DC and DC-DC. A 10 kW prototype has been built and verified the proposed topology and modulation scheme. The power loss on clamping device is negligible (0.02% of the output power). At the same time, the tested voltage stresses across all 1.7 kV SiC MOSFETs are less than 1.1 kV at 2 kV dc-link voltage.