Submodule Fault Detection and Location Method for Modular Multilevel Converter Based on the Voltage Variation Observations

Submodule (SM) fault detection and location (FDL) is essential for the reliable operation of modular multilevel converters (MMCs). Once SM failures occur, the capacitor voltages of faulty SMs will be out of control and deviate from the rated value. As analyzed in this paper, in normal state, the charging abilities of driving signals are constant in one fundamental period. Thus, the voltage variation of SMs in one fundamental period should coincide with the charging ability of driving signals applied to them. So this paper proposes an FDL method based on the capacitor voltage variation observations, which monitors the health state of SMs by comparing the expected voltage variations with the measured ones. The proposed method can detect and locate the faulty SM simultaneously in no more than two fundamental periods and requires no arm current measurement. Effectiveness of the proposed method and influence of capacitance inconsistency are validated by simulation results of a three-phase 101-level MMC in MATLAB/Simulink.