Capacitor ESR and C Monitoring in Modular Multilevel Converters

The capacitor is one of the weakest components in the modular multilevel converter (MMC). The rise of equivalent series resistance (ESR) is a prominent character to monitor the lapsed capacitor, but current research works only focus on capacitance and neglect ESR of capacitors in the MMC. This article proposed a sorting-based monitoring strategy for capacitors in the MMC, which monitors not only the capacitance but also the ESR of capacitor. This article reveals the relationship among the capacitor's ESR, capacitance, current, and energy. Based on the relationship, the ESRs and capacitances of submodule capacitors in the arm are indirectly sorted, respectively, and only the capacitor with biggest ESR and the capacitor with smallest capacitance in the arm are monitored. The proposed strategy not only realizes both ESR and capacitance monitoring in the MMC, but also proposes a simplified monitoring algorithm for MMCs with a large number of capacitors. The simulation and experimental results confirm the effectiveness of the proposed monitoring strategy for MMCs.