Fault-tolerant strategy for modular multilevel converter with nearest level modulation in HVDC system

• Published in: International journal of electrical power & energy systems 2024-07, Vol.158, p.109970, Article 109970
• Main Authors: Geng, Zhi, Han, Minxiao, Xie, Wenqiang, Yang, Yong
• Format: Article
• Language: English
• Subjects: Fault-tolerant strategy; High voltage direct current (HVDC); Modular multilevel converter (MMC); Nearest level modulation (NLM); Submodule fault
• ISSN: 0142-0615; 1879-3517
• DOI: 10.1016/j.ijepes.2024.109970

•The faulty operation of MMC with hot-reserved SMs is analyzed.•NLM corrector based fault-tolerant strategy for high-voltage MMC is proposed.•The strategy features simplicity, low voltage stress and little influence scope. The reliable and consistent operations of modular multilevel converters (MMCs) under fault conditions are crucial for high-voltage and high-power applications. To strengthen the performances of MMCs under submodule (SM) faults, a fault- tolerant strategy based on the nearest level modulation (NLM) is proposed in this paper. According to the changed AC component in the faulty arm voltage, this method adds a corrector in NLM, which remedies the faulty arm voltage by adjusting the number of inserted SMs for the faulty arm. Then, the faulty operation can be recovered to the normal. The corrector is simple to realize and can effectively suppress the odd-order circulating currents. Under the proposed method, only the ripples of the capacitor voltages in the faulty arm rise. The average voltage stress on each capacitor is the same as that in normal operation since the rated capacitor voltage in the faulty arm has no rise. No measure and influence impose on healthy arms. With features of simplicity, low voltage stress and little influence scope, the proposed strategy is fit for high-voltage MMCs. The feasibility of the proposed strategy is verified by the simulation results with the professional tool Matlab/Simulink.