Capacitor Condition Monitoring Method for Low-Capacitance StatComs: An Online Approach Using the Inherent Second-Harmonic Oscillations

The cascaded H-bridge low-capacitance static compensator (StatCom) deliberately reduces the capacitor size while allowing large oscillations in capacitor voltages. When a capacitor deteriorates, its capacitance decreases or/and its equivalent series resistance (ESR) increases, compromising StatCom performance and safety. For this reason, the condition monitoring of the capacitors is important to schedule maintenance before failure. This letter introduces a cost-effective and nonintrusive method to monitor the condition of capacitors online. The proposed method offers real-time monitoring without requiring additional hardware or signal injection. The method uses averaged low-frequency signals instead of instantaneous high-frequency signals that can be corrupted by undesired high-frequency noise. Specifically, the method takes advantage of the inherent twice-fundamental-frequency oscillations on the capacitor voltage and current to identify the ESR and capacitance values. The method takes into account the influence of antialiasing filters required for sampling process. The letter shows experimental results that validate the fast and accurate performance of the proposed capacitor condition monitoring.