Condition Monitoring for Submodule Capacitors in Modular Multilevel Converters

This letter proposes a method for the condition monitoring of submodule (SM) capacitors in modular multilevel converters (MMCs) without additional circuitry or computationally heavy algorithm. The proposed method leverages the discharging curve of SM capacitors in connection with the parallel bleeding resistors. It is independent of the MMC control and modulation schemes. Moreover, it potentially does not require thermal and load-related calibration for capacitor degradation monitoring. The principle, case study, and proof of concept of the proposed method are presented.