Condition Monitoring for Capacitors in Modular Multilevel Converter based on High-frequency Transient Analysis

Condition monitoring (CM) methods applied for power electronics can provide effective information for predictive maintenance and prevent unexpected system downtime. This paper proposes a non-invasive and in-situ CM method for capacitors in modular multilevel converters. Unlike the conventional methods that monitor low-frequency signals, the proposed method focuses on high-frequency transient analysis. By analyzing the transient voltage at the capacitor's charging moment with wavelet decomposition, the proposed method can estimate the capacitor's equivalent series resistance in situ. Moreover, the proposed method based on high-frequency transients is decoupled from system operating states, while the conventional low-frequency signals are often affected by operations (e.g., loads, environments, etc.). Finally, the effectiveness of the proposed method has been validated in a 14kW case study by simulation.