A Non-invasive Online ESR Estimating Method for DC-Link Capacitors of UPS

It is necessary to monitor the aging state of aluminum electrolytic capacitors (AEC) because of their short life span. Based on the simplified capacitor equivalent circuit, equivalent series resistance (ESR) is selected as an aging indicator of the capacitor. By using a band-pass filter to extract the AC component of the dc-link voltage and current, the active power consumed by the capacitor is calculated to obtain the ESR estimation. The proposed method does not require additional sensors and the algorithm is simple and easy to implement. Simulation results show that the method can keep its effectiveness under complex operating conditions.