Voltage Balancing Control Strategy for Hybrid MMC Based on BADS-Optimized Second Harmonic Injection

Ying Fang, Jinlong Gu, Fang Liu, Yanhua Liu () and Shuo Shi
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Ying Fang: State Grid Anhui Electric Power Co., Ltd. Chuzhou Power Supply Company, Chuzhou 239000, China
Jinlong Gu: State Power Investment Corporation Green Energy Co., Ltd., Beijing 101499, China
Fang Liu: Beijing Institute of Structure and Environment Engineering, Beijing 100076, China
Yanhua Liu: School of Electrical Engineering, Shandong University, Jinan 250061, China
Shuo Shi: State Grid Shandong Electric Power Research Institute, Jinan 250000, China

Energies, 2025, vol. 18, issue 22, 1-18

Abstract: Under overmodulation conditions, the capacitor voltages of half-bridge and full-bridge submodules in hybrid modular multilevel converters (MMCs) may become unbalanced. This imbalance not only gives rise to overvoltage stress on submodule capacitors, jeopardizing equipment safety, but also degrades power quality and may even trigger operational instability. To address this issue, this paper proposes a minimum second harmonic circulating current injection method based on Bayesian Adaptive Direct Search (BADS) within the overall framework of model predictive control for MMCs. The method efficiently solves complex objective functions by alternately performing local Bayesian optimization and global grid search. Optimal second harmonic injection values under different modulation indices are obtained through offline computation and curve fitting. This approach achieves dynamic capacitor voltage balancing across a wide modulation range while minimizing operational losses caused by harmonic currents.

Keywords: hybrid modular multilevel converter; Bayesian adaptive direct search; second harmonic injection; model predictive control; capacitor voltage balancing (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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