A Concurrent Diagnosis Method of IGBT Open-Circuit Faults in Modular Multilevel Converters

The insulated-gate bipolar transistor (IGBT) is one of the most vulnerable components in the modular multilevel converter (MMC). One or more IGBT open-circuit faults may deteriorate the output performance of the MMC and even destroy the MMC systems. In this article, a concurrent and direct fault diagnosis method has been proposed. The capacitor voltages are estimated with an amending Kalman filter (KF). By comparing the measured and estimated values, the corresponding faulty submodule (SM) can be detected directly and quickly. The diagnosis process of SMs is independent of each other so that all the SMs can be monitored in real time and the diagnosis time will not increase with multiple open-circuit faults occurring. The proposed method can also identify which IGBT has occurred open-circuit fault in the faulty SM and has no special requirement for the modulation method. In addition, the amending KF has excellent robustness to the transient process and can overcome the divergence problem, which is applicable in the complex nonlinear MMC system. The effectiveness of the proposed fault diagnosis method is confirmed by simulation in MATLAB/Simulink and experimentation in a single-phase MMC prototype with eight SMs per arm.