An Open-Circuit Fault Detection and Localization Scheme for Switch Failures in Modular Multilevel Converter Based on Arm Voltage Analysis

Modular multilevel converter (MMC) is a promising configuration in high voltage direct current (HVDC) systems, medium voltage high power motor drives, and active filters. A large number of submodules (SMs) in this structure increases the probability of switch failure. The submodule's switch open-circuit fault is a common failure in MMC, which requires a rapid diagnosis. This paper proposes a new fast open-circuit fault detection and localization scheme. The proposed scheme uses the arm voltages to diagnose the faulty switch. The presented method compares the real value of arm voltage with the expected value derived from switching signals and capacitor voltages and detects the fault once they are not equal. To locate the faulty SM, the real value and expected value of arm voltage are compared in certain moments of a cycle. Using this approach, the fault will be detected and located quickly, that cause the SM capacitor voltages do not deviate from their nominal voltages. Thus, the voltage stress of the switches remains within the permissible range. Simulation results in MATLAB/Simulink environment show the correct performance of the proposed methods.