A 3.3 kV Silicon Carbide MOSFET Based Building Block for Medium-Voltage Ultra-Fast DC Chargers

The growing demand for the ultra-fast DC charging stations needs the direct connection to the medium-voltage (MV) distribution grid, which can be achieved through the solid-state transformers (SST) as opposed to solutions using line frequency transformers (LFT). By using the MV high current silicon carbide (SiC) modules, which are becoming more available than before, the architecture of SST can be significantly simplified with much less number of series-parallel modular cells. In this work, we investigate the feasibility and present the development of a 3.3 kV SiC based full bridge building block. Then a MV dual active bridge (DAB) with 2 kV DC input and 800 V DC output, which is an essential unit in the MV DC charger, is prototyped using the developed building block. Compared to the use of modules rated at 1.7 kV or lower, the presented DAB can reduce the number of series cells in half, since the DC bus voltage for each cell can be raised from 1 kV to 2 kV. Extensive characterizations, e.g., switching tests, thermal tests, and etc., have been carried out for the 3.3 kV SiC module to extract key information to guide the electro-thermal co-design of the MV DAB system.