Improved DC Transformer Submodule with High Input voltage

In order to improve the power density of DC transformer (DCT), this paper proposes one novel DCT submodule based on three-phase dual-active-bridge (DAB) converter. By connecting three-phase legs in series and adding blocking capacitors, the input voltage of single submodule (SM) can be improved without increasing the voltage stress of switches. Hence, compared to conventional DCT based on full-bridge DAB converter, the number of SMs is reduced and power density can be improved. Based on the analysis of operation principle, design rules of main parameters and basic control strategy of single SM are presented, and the feasibility is verified with 600–200V/2kW prototype.