Journal of Electrical Engineering ›› 2023, Vol. 18 ›› Issue (4): 143-151.doi: 10.11985/2023.04.016

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Fault-tolerant Control of MMC Redundant Sub-module Cold and Hot Hybrid Standby Based on NLM

XIA Changjiang1(), TANG Huan1(), HAN Minxiao2(), LIN Jiaxin1   

  1. 1. State Grid Meishan Power Supply Company, Meishan 620000
    2. School of Electrical and Electronic Engineering, North China Electric Power University, Beijing 102206
  • Received:2023-01-31 Revised:2023-06-18 Online:2023-12-25 Published:2024-01-12

Abstract:

To improve the operational reliability of modular multilevel converter(MMC), the MMC arm is usually equipped with redundant submodules. Based on redundant MMC, the fault tolerance strategy of hot and cold hybrid standby is improved. The control complexity and power loss of MMC with different fault tolerance strategies are analyzed and compared. In order to complete the hybrid standby fault-tolerant strategy, a charging control strategy for the cold standby sub-module of MMC is proposed based on the nearest-level modulation(NLM) principle, which reduces the influence of the cold standby sub-module charging process on the output performance of MMC. In addition, the method of setting the number of hot and cold standby submodules is proposed. Finally, a 21-level three-phase MMC model is built based on the PSCAD/EMTDC simulation platform. The simulation results show that the improved mixed-reserve fault-tolerant strategy can effectively reduce the fluctuation of the fault-tolerant transition process, and verify the effectiveness and feasibility of the fault-tolerant control strategy.

Key words: Modular multilevel converter(MMC), sub-module failure, sub-module charging control, redundant fault-tolerant control, hot and cold hybrid standby

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