Losses Analysis of MMC in Medium Frequency Medium Voltage DAB Converter for Charging Station

Medium voltage (MV) modular multilevel converter (MMC) is an attractive candidate for multi MW fast charging station (FCS) to transfer high power with high efficiency, and a medium-frequency (MF) isolated dual active-bridge (DAB) DC/DC converter is needed to step down the voltage in this application. In this regard, MMC-based isolated DAB DC/DC converter is a good candidate to be used in FCS. In MMC-based isolated DAB DC/DC converter, Quasi-two-level (Q2L) waveform is the preferred waveform for the AC side voltage of MMC due to low dv/dt and small capacitor of submodules. The analysis on power losses of MMC in this application and with this specific AC voltage waveform is an important issue for a cellular high-efficiency design that requires more investigation. This paper provides an analysis to estimate switching and conduction losses of MMC used to produce a quasi-two-level waveform which can be used among the others also in DAB applications. Finally, the effectiveness of the losses analysis is verified by simulation results, and the experimental results are used to investigate the behavior of MMC in this application.