Condition Monitoring of Electrolytic Capacitor based on ESR Estimation and Thermal Impedance model using Improved Power Loss Computation

Abstract

Aluminium Electrolytic Capacitors (AEC) are indispensable in applications where high capacitance per unit volume and low cost are preferred. However, it is also one of the most failure-prone components in a power converter system. As AEC is an electrochemical device, which follows Arrhenius law, the most important life-deciding factor of an AEC is its operating temperature [1]. In this paper, a condition monitoring system for AECs is proposed based on the accurate estimation of equivalent series resistance (ESR) and operating temperature. Operating temperature is estimated using the thermal impedance model based on improved power loss calculation methodology. The proposed method computes power loss using the capacitor voltage and current in contrast to the existing methods [4] - [7] which uses capacitor current and ESR to estimate the power loss. Thereby, it avoids the issue of ESR variation with ageing and temperature which may give erroneous results with ageing in case of stored look-up tables for ESR. ESR estimation is based on the method proposed in [14]. As ESR is the most widely used degradation indicator, the ESR and operating temperature can be used to estimate the present health status of an AEC.