A capacitor voltage balancing method for a three phase modular multilevel DC-DC converter

Abstract

A capacitor voltage balancing method for a three phase modular multilevel DC-DC converter (MMDC) is proposed in the paper. The MMDC is derived from a three phase DAB and a modular multilevel converter (MMC) and inherits desirable features of both topologies. To guarantee stable operation of the MMDC, submodule (SM) capacitor voltages are required to be balanced. The proposed balancing method is to assign the gate signals to SMs according to the SM capacitor voltages and net charge: assign the gate signals with the higher net charge to the SMs with the lower capacitor voltage and vice versa. With the proposed balancing method, the converter can operate in wider voltage ranges and the transformer primary side voltage can generate more level staircase waveforms to reduce the dv/dt stress on the MF transformer. The simulation and experimental results are provided to verify the proposed method.