Control Strategy for Asymmetric Faults on the Low-Frequency Side of a Sparse Modular Multilevel Converter

作者：Yuwei Sun, Shengce Wang, Chao Fu, Zelin Zhang, Guo-Liang Zhao, Yunfei Xu, Bao Liu, Jia Chen · 发表于：Electronics · 年份：2025 · DOI：10.3390/electronics14030426 · 被引用次数：3 · 研究领域：HVDC Systems and Fault Protection、High-Voltage Power Transmission Systems、Power Systems Fault Detection

Sparse modular multilevel converters (SMMCs) are a new type of lightweight high-voltage large-power AC/AC converter that significantly reduces the number of components compared to modular multilevel matrix converters (M3Cs). This study proposes a fault ride through a control strategy for SMMC to address the issues of arm energy imbalances and valve-side overvoltage, which occur during asymmetric faults on the low-frequency side. First, we establish models of the energy deviation of the arms under asymmetric short-circuit faults on the low-frequency side of SMMC. We also study the influence mechanism of the control strategies on the arm energy imbalance during faults. On this basis, an arm energy balancing strategy based on zero-sequence voltage injections combined with AC voltage control is proposed; this can achieve arm energy balance and suppress the negative sequence current and overvoltage of the SMMC. Finally, we construct a simulation model of an offshore wind power low-frequency transmission system based on the SMMC. The simulation results show that the proposed energy balance strategy can realize the stable operation of the low-frequency transmission system (LFTS) under asymmetric faults on the low-frequency side, that the maximum capacitor voltage deviation during the fault does not exceed 10% and that capacitor voltage returns to normal 0.25 s after the fault occurs.