Online Monitoring for Sub-module Capacitance in Modular Multilevel Converter with Four Sampling Points of Capacitor Voltage

Reliability performance is a critical challenge for modular multilevel converters (MMCs) due to the high number of sub-modules (SMs). In order to fulfill the reliability performance, condition monitoring (CM) for capacitors in MMC SMs, which are heavily loaded and vulnerable components, is imperative to be employed. This paper proposes a novel online capacitance CM method for SM capacitor, and only four instantaneous value of capacitor voltage with specified phase information are required to obtain the capacitance of SM. A mission profile emulator for individual SM in MMC is designed and employed to validate the effectiveness of the proposed approach. Finally, simulation and experimental results are given to demonstrate the proposed method.