Electrolytic capacitor thermal model and life study for forklift motor drive application

Electrolytic Capacitors (E-Cap) are commonly used as ripple-current filters at the input of the inverter of AC motor drive control systems used in electric vehicles. These capacitors have a ripple-current rating but may in fact be used at values higher than this rating. Ripple current causes heating of the E-Cap, which can significantly impact its life and thus be a major influence on the reliability of the entire system. Here we discuss how to develop a thermal model of the E-Cap that can be used in the system control algorithm to monitor, and if necessary, reduce transient core temperature response of the E-Cap to maintain the system life and increase reliability. The model described in this paper is a second-order thermal model used to allow operational conditions that limit the temperature increase to <; 30°C. An E-Cap life study will be also discussed for the worst-case environment temperature.