A Dynamic Threshold Adjustment-Based Low-Switching-Frequency Voltage Equalization Strategy for MMC

This paper addresses the capacitor voltage balancing issue of submodules (SMs) in Modular Multilevel Converters (MMCs) operating under low switching frequencies by proposing a voltage balancing control strategy based on dynamic threshold adjustment. First, a dynamic model of SM capacitor voltage in MMCs is established, and the causes of capacitor voltage imbalance are analyzed. Then, based on the coupling relationship between switching frequency and voltage balancing, and the imbalance model under dynamic operating conditions, a dynamic threshold adjustment strategy is designed. A Fuzzy Logic Controller (FLC) is employed to dynamically adjust the voltage imbalance threshold in real time, ensuring capacitor voltage balance while optimizing the switching frequency and reducing system losses. Simulation results show that the proposed strategy can effectively maintain SM capacitor voltage balance under low-switching-frequency conditions, thereby improving system stability.