Capacitor Size Comparison on High-Power DC-DC Converters with Different Transformer Winding Configurations on the AC-link

This paper compares the capacitor requirement of the modular multi-level converter based dual-active-bridge (MMC-DAB) and the controlled transition bridge based dual-active-bridge (CTB-DAB) DC-DC converters. Three winding configurations, namely YY, DD, and YD, are considered for the AC-link's medium-frequency transformer (MFT). It is shown that for a specific inverter topology (i.e., MMC or CTB), the YY and DD connections of the MFT results in identical energy storage requirements for the converters. Moreover, it is demonstrated that the YD connection reduces the capacitor requirements of the converters considerably. In the best case, the capacitor requirement can be reduced for the MMC-DAB and the CTB-DAB by 30% and 40%, respectively. A comparison between the converters showed that the YY-connected MMC-DAB (the YD-connected CTB-DAB) has the highest (the lowest) energy storage requirement. Additionally, it is shown that the YD-connected CTB-DAB can achieve up to 78% (58%) less energy storage compared to the YY-connected MMC-DAB in the best case (worst case).