Journal of Power Electronics

The Korean Institute of Power Electronics (전력전자학회)
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Capacitor voltage balancing method for hybrid modular multilevel converters based on second-harmonic voltage injection

  • Hongxu Li (Department of Automation Engineering, Nanjing University of Aeronautics and Astronautics) ;
  • Qin Wang (Department of Automation Engineering, Nanjing University of Aeronautics and Astronautics) ;
  • Qunfang Wu (Department of Automation Engineering, Nanjing University of Aeronautics and Astronautics) ;
  • Lan Xiao (Department of Automation Engineering, Nanjing University of Aeronautics and Astronautics) ;
  • Jinbo Li (Department of Automation Engineering, Nanjing University of Aeronautics and Astronautics)
  • Received : 2023.03.04
  • Accepted : 2023.12.08
  • Published : 2024.04.20
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Abstract

Due to different output voltages, capacitor voltage imbalance occurs between half-bridge sub-modules (HBSM) and full-bridge sub-modules (FBSM) in hybrid modular multilevel converters (MMCs) under a boosted modulation index (m). To address this issue, a capacitor voltage balancing method based on second-harmonic voltage injection is proposed in this paper. The mechanism of the proposed method is to eliminate the DC component in the charging power of sub-modules under the restriction that the HBSM cannot output negative voltage. The proposed method is divided into two cases according to m. Case 1 is used when m ≤ 1.4, while Case 2 is implemented when m > 1.4. When compared with similar capacitor voltage balancing methods, the proposed SVI method has a simpler structure that can greatly reduce the number of computations. Simulation and experimental results verify the effectiveness of the proposed capacitor voltage balancing method.

Keywords

Acknowledgement

This work was supported in part by the National Natural Science Foundation of China under Grant 62371233 and 52177049, in part by the Natural Science Youth Foundation of Jiangsu Province under Grant BK20210305, in part by Nanjing University of Aeronautics and Astronautics Youth Science and Technology Innovation Funding under Grant NS2022031 and NS2023053, in part by the Fundamental Research Funds for the Central Universities under Grant NJ2022014, in part by Aviation Science Foundation Project under Grant 2022Z024052003, and Nanjing University of Aeronautics and Astronautics prospective research project and Grant ILA220531A23.

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