Modeling of the Isolated Modular Multilevel DC-DC Converter by Considering the Magnetizing Inductance of the High-frequency Transformer.

With the rapid development of distributed energy resources, the Isolated Modular Multilevel DC-DC (IMM DC-DC) converter is becoming a promising solution for the interconnection of Medium Voltage (MV) and/or High Voltage (HV) DC grids. In this paper, the detailed mathematical model of the IMM DC-DC converter based on harmonic analysis is firstly established by considering the magnetizing inductance of the high-frequency transformer. Then, the real and reactive powers, transformer primary and secondary side currents, arm currents, and capacitor voltage ripples can be accurately determined. Due to the existence of the large arm inductance, the magnetizing inductance of the transformer is no longer negligible. Comparisons between the study results confirm that the magnetizing inductance has a significant impact on each of the aforementioned variables. The proposed analytical model can help achieve accurate sizing of the major components of the IMM DC-DC converter. The presented analysis is validated by both simulation in the Matlab/Simulink environment and experiment.