IEEE Access (Jan 2021)

Research on Multi-Port DC-DC Converter Based on Modular Multilevel Converter and Cascaded H Bridges for MVDC Applications

  • Guanglin Sha,
  • Qing Duan,
  • Wanxing Sheng,
  • Chunyan Ma,
  • Caihong Zhao,
  • Yao Zhang,
  • Jiachen Tian

DOI
https://doi.org/10.1109/ACCESS.2021.3072161
Journal volume & issue
Vol. 9
pp. 95006 – 95022

Abstract

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Aiming at the low-voltage DC distribution network system and combining the characteristics of F2F structure and ISOP-DAB structure DC transformer, this paper proposes a DC transformer structure based on modular multilevel converter (MMC) and cascaded H-bridge. First of all, this paper analyzes several different cases. Case 1 proposes a type of equal carrier-phase-shift pulse-width modulation (CPS-PWM) of MMC, which can produce an equal five-level voltage waveform. In the meanwhile, another unequal CPS-PWM control is proposed to produce an unequal five-level voltage waveform. According to the descriptions of case 2, the quasi-square-wave-modulation method with a wide gain range can greatly reduce the insulation design difficulty of the intermediate AC side high-frequency transformer and the voltage stress on the AC side. Case 3 demonstrates the extended-phase-shift (EPS) control of three-port DC-DC converter. Combining the voltage sorting algorithm of voltage sequencing and cyclic switching, a strategy of voltage equalization for grouped capacitors is proposed. Considering the various application scenarios of actual working conditions, the soft switching characteristics and multi-port power characteristics of the DC transformer are analyzed. In order to verify the feasibility of the DC transformer structure and its control strategy, a simulation model was built in Matlab/Simulink and the results were verified. The results are in accordance with the theoretical analysis.

Keywords