A method for predicting the expected life of bus capacitors

Predicting the expected life of motor drive bus capacitors is complicated by several factors: the equivalent series resistance of aluminum electrolytic capacitors is frequency and temperature sensitive; the ripple current is a composite waveform; and the capacitor expected life is very sensitive to operating temperature. This paper describes a method that addresses all these factors by developing separate models for capacitor equivalent series resistance, motor drive circuitry, heat transfer conditions and capacitor life.