Integrated fault diagnosis method for IGBT open circuit fault and voltage sensor fault in MMC submodule

The MMC system contains numerous submodules. The frequent occurrence of switch open-circuit fault and submodule voltage sensor faults have similar fault characteristics, leads to degraded system reliability. This paper proposes an integrated diagnosis method for submodule IGBT open-circuit faults and voltage sensor faults based on a sliding mode observer. Firstly, the fault detection variable is designed based on the actual bridge arm voltage values and the measured bridge arm voltage values to detect the occurrence of fault and to locate it to the bridge arm level. Then, for each submodule of the faulty bridge arm, a sliding mode observer is designed to estimate the submodule capacitor voltage value, which is compared with the measured value to further locate the fault to a specific submodule. Finally, the submodule capacitor voltage information is utilized to distinguish between specific IGBT upper and lower open-circuit faults and three typical fault types of voltage sensors. The effectiveness and robustness of the proposed fault diagnosis algorithm are validated through hardware-in-loop simulation results.