SiC: Technology Enabler for MV DC/DC Galvanically Insulated Modular Converters

In this paper, the use of 3.3 kV SiC MOSFETs, Fast Si IGBTs and the mix of both in the so called Cross-Hybrid Switch (XS) and Bimode Cross-Hybrid Switch (BXS) are considered for their application on Galvanically Insulated Modular Converters (GIMC) cells. The semiconductors typically operate under Soft Switching conditions to allow high frequency operation resulting in size and weight minimization while keeping a high efficiency. The high frequency (10 kHz) and Soft Switching operation in the selected semiconductors have been first evaluated by applying 2D semiconductor device simulations. The simulation results allow to identify the impact of device parameters such as the Si IGBTs Lifetime adjustment and the Si IGBT - SiC MOSFET chip surface ratio on the BXS devices, over the on-state and switching losses. Accordingly, different 3.3kV dual HiPak testing samples have been implemented and experimentally evaluated on a 200 kW DC/DC GIMC cell test bench. The comparison between the 3.3 kV Fast Si IGBTs, SiC MOSFETs and BXS shows clear functional benefits of using MV SiC MOSFETs in resonant mode operation, allowing an increase of the GIMC cell power capability by 30 - 35 % for the same module current rating compared to the use of Fast IGBTs. In a similar way, the BXS devices can provide and intermediate power capability increase of around 20-25%, minimizing the installed Si and SiC chip area that can be used as an enabler for improvement of the GIMC technology impacting the cost and performance of the semiconductor devices applied on the GIMC cells.