Meaurement of Electrical Parameters of Electrolytic Capacitors Using Real-World Drive Waveforms for State-of-Health Determination

Electrolytic capacitors form an important part of most drive systems. Consequently a method of determining the state-of-health of these capacitors without having to remove them from the system would be of value. In this paper a method of achieving this is proposed. This is achieved by measuring the current through and the voltage across the dc link capacitor within a brushless dc motor drive; from these values the impedance spectrum is calculated. From these measurements the capacitance and resistance values of the capacitor are calculated. This technique forms a useful prognostic tool for power electronic drive systems where changes to these electrical parameters are a good indicator of the state-of-health of the capacitor. Real-world results taken from an experimental system demonstrate that increases in capacitor resistance can be clearly observed.