A Submodule Insertion Window-Based Capacitor Condition Monitoring Method for Modular Multilevel Converters

Capacitors are key components of modular multilevel converters (MMC), and capacitor condition monitoring is a crucial issue in MMC. This paper introduced a capacitor monitoring method based on submodule (SM) insertion windows to enhance the reliability of the MMC. Firstly, the voltage difference between the reference SM and other SMs is monitored to assess the capacitor condition of the SMs. Secondly, for the selected SM capacitors in abnormal state, an insertion window for the SM is extracted by introducing a time delay factor, and the subsequent capacitance calculation is performed based on the voltage changes of the reference SM and other SMs within the monitoring interval. The proposed monitoring method can effectively identify the abnormal capacitor state and accurately calculate the capacitance value. Moreover, the proposed method does not affect the normal operation of the MMC. Finally, simulation analysis and experimental validation are performed to verify the effectiveness of the proposed method.