A Fault‐Tolerant Control Method for Grid‐Connected MMC Employing Compound Mutual Inductance Charge Channel

Abstract

For the long‐distance grid connection of offshore wind farms, high‐voltage direct current (HVDC) transmission systems based on modular multilevel converters (MMC) are now the predominant technical solution. Although the MMC offers high voltage output capability, its reliance on a large number of continuously operating IGBTs renders it prone to faults. To address open‐circuit faults in IGBTs within MMC submodules (SMs) and ensure grid‐connection reliability, this paper employs a compound mutual inductance charge channel and a modulated wave reconstruction method after MMC faults. The fault‐tolerant control mechanism of the proposed method under typical fault conditions is thoroughly analyzed, which proves that the capacitor in the faulted submodule can be discharged by using this method. Additionally, this method operates independently of voltage and current sensor data, enabling sensorless operation. The results show that after two types of faults occur and the proposed fault‐tolerant method is employed, the voltage fluctuation rate of the submodule capacitors transitions from a divergent state to a stable fluctuation, with the fluctuation rate not exceeding 4.53%, and the THD of the output current is reduced by 93.82% and 98.12%, respectively. Comprehensive simulation and experimental studies substantiate the proposed method, confirming its feasibility and effectiveness.