Open-circuit fault detection and isolation for modular multilevel converter based on sliding mode observer

This paper presents a fault detection and isolation (FDI) method for a Modular Multilevel Converter (MMC). This method can locate an open-circuit faulty device accurately and quickly. Based on a sliding mode observer (SMO) and a switching model of a half bridge, the approach is to assume the location of the fault, modify the observer equation and then compare the measured and observed states to verify, or otherwise, the assumption for possible fault locations. This technique requires no additional measurement elements and can easily be implemented in a microcontroller. The operation and robustness of the proposed method are confirmed using simulation results.