Voltage Fluctuation Based Monitoring Scheme of Submodule Capacitors in Modular Multilevel Converter

Submodule (SM) capacitor is one of the critical components in modular multilevel converter (MMC) and will gradually age with the working time increasing, which brings potential challenges for the systems reliability. This article proposes a novel online capacitance monitoring scheme for SM capacitors. Based on the voltage variations on rising and falling edge of power switches' operation, the aging capacitors can be monitored in real-time. Meanwhile, the proposed capacitance monitoring scheme is based on the mathematical model of the systems and has good applicability. It has no any impact on the normal operation of the MMC systems, no special requirement for the modulation method and no need for additional hardware circuits. For the proposed capacitance monitoring scheme, it can be implemented in parallel mode or sequential mode based on the field-programmable gate array (FPGA). Finally, simulation in MATLAB/Simulink and experimentation in a single-phase MMC prototype with 8 SMs per arm are built to confirm the effectiveness of the proposed method.