Lifetime of Electrolytic Capacitors in Regenerative Induction Motor Drives

Electrolytic capacitors are normally used as the energy storage element in the DC link of voltage-source converters because of their high density. Unfortunately, they are bulky and their lifetime is significantly reduced by their operating temperatures. Thus, reducing, or even better eliminating, the amount of electrolytic capacitors is an important goal since the capacitor could be a single point of failure. This paper analyses the lifetime of electrolytic capacitors used in the DC link of an induction motor (IM) drive whose front end consists of a controlled rectifier. The latter controls the DC-link voltage and input power factor. Both, the inverter and rectifier operate under space vector modulation (SVM). The peak ripple voltage, ripple current, core temperature and lifetime of electrolytic capacitors ranging from 200 muF to 12000 muF are calculated for different values of the source inductance and the ambient temperature when the IM is operating at rated load. In addition, the IM ripple torque and speed response time are also calculated and an 8.2 muF ceramic capacitor case is included for completeness. The evaluation is based on Matlabtrade/Simulink simulation results of the IM drive that are used to calculate harmonic components of the different current waveforms. The results show that the lifetime of electrolytic capacitors is significantly reduced for decreasing capacitance values. The main reason is that the effective series resistance (ESR), and hence heat losses, increases for decreasing capacitance values leading to increased core temperatures that are detrimental to the capacitor lifetime