Contents 1 Introduction
Electrolytic capacitors are widely used in power electronic systems, e.g. DC-link applications [1], and hence their relatively high failure rate affect the overall system reliability. Metal oxide semiconductor field effect transistors (MOSFET) and electrolytic capacitors have the highest degradation and failure rates among all power converter components, i.e. 31% for MOSFETs and 60% for electrolytic capacitors [2]. A decrease in electrolyte volume caused by vaporization or leakage results in an increase in the equivalent series resistance (ESR) of the capacitor and a decrease in its capacitance over time. The increase in ESR results in internal heating which, in turn, causes further evaporation of the electrolyte and consequently a further increase in the ESR and decrease in capacitance. Eventually, this gradual degradation may cause the complete loss of the capacitor functionality and the corresponding downtime of the power electronic system. Therefore, early detection of the capacitor degradation (also known as capacitor ageing) may contribute to the reduction of catastrophic failure. This can be achieved by monitoring the ESR and capacitance on-line since these two electrical parameters give an indication of the device condition. In this regard, the end-of-life (EoL) of an aluminum electrolytic capacitor is reached when its ESR doubles and/or its capacitance decreases by 20% [3] [4].
