Discharge-based condition monitoring for electrolytic DC-link capacitors

Electrolytic capacitors are among the most vulnerable components in power electronic converters, risking their efficient and electrically stable operation. This is due to the decreasing capacitance under long-term stress. Thus, monitoring of the capacitance is imperative for ensuring proper converter's operation. This paper proposes a low-invasive method for condition monitoring of the health-status of DC-link electrolytic capacitors. The proposed method is based on the estimation of the remaining capacitance by analyzing the DC-link voltage decay during the shut-down phase of the power converter. In the proposed condition monitoring method, the temperature dependency and the physical behaviour of the electrolytic capacitors are investigated and compensated in the developed state of health estimation model. The proposed method has been validated experimentally using a full-scale power converter rated at 200 kW. The experimental validation includes accelerated degradation tests of capacitors under various temperature and pre-charge operating conditions, as well as field data from 153 converters, which are analyzed with the proposed method.