Degradation Analysis of DC-Link Aluminium Electrolytic Capacitors Operating in PWM Power Converters

Abstract

The most common failure mode of aluminium electrolytic capacitor is the so-called wear out fault. It is caused by the high core temperature of the capacitor. Therefore, life cycle calculations generally use temperature data to estimate degradation level. Core temperature-based life cycle calculations can consider different current loads on capacitors. The calculation method uses scaling factors for different ripple current waveforms. However, it is not observed that temperature only is responsible for aging, but current waveform also influences the level of degradation. Therefore, sinusoidal and PWM-loaded capacitor tests were performed under the same temperature conditions. The results show that the pore distribution of aluminium anode foil has changed during the test. The pore diameter reduces and it leads to an increase in the ESR value and decrease in the capacitance, electrolyte amount and weight. Comparative results show that the PWM-loaded capacitor is more degraded than the capacitor loaded by sinusoidal test current.