Health Monitoring of DC link Capacitors

Electrolytic and metallized polypropylene film (MPPF) capacitors are among the most popular capacitors used in electronic equipments. The choice of capacitors is of major importance because one of the most frequent causes of the equipment breakdowns results from the failure of capacitors, and will therefore determine the overall lifetime of the system. Electrolytic capacitors present higher capacity per volume unit and lower cost than MPPF capacitors; however, they appear as the most life-limiting components exhibiting a high failure rate. MPPF are a good alternative to electrolytic capacitors thanks to their high dielectric breakdown strengths, low dissipation factors and good stability over a wide range of frequencies and temperatures. Even though MPPF capacitors are very reliable components due to their unique self- healing capability, they are not free of failures and they release noxious gases in this case. Therefore, suitable diagnostic techniques are needed to prevent catastrophic failures. The typical failure mode of electrolytic and polypropylene film capacitors lays on the increase of the capacitor Equivalent Series Resistance (ESR) and the decrease of its capacitance. This paper presents an approach for the monitoring of the capacitor’s electrical parameters in function of the ageing time when used as DC-link capacitors. A comparison between the film and electrolytic technologies will be also made in this paper.