Condition monitoring of DC-link capacitors in drive system for electric vehicles

This paper proposes an online DC-link capacitor condition monitoring scheme for electric vehicles. Capacitance of both electrolytic and metallized polypropylene film (MPPF) capacitors decreases as the capacitors deteriorates, so that the proposed scheme utilizes the capacitance as the parameter of diagnosis of the DC-link capacitor. Every time the drive system of electric vehicles is turned on and off, the DC-link capacitor is diagnosed by estimating its capacitance. In order to estimate the capacitance, the DC-link capacitor is discharged through the traction motor, and its capacitance is estimated from its voltage and current information. The voltage and current of the DC-link capacitor can be acquired using existing sensors, and no additional hardware is required. During the discharge of the DC-link capacitor, the current flowing through the DC-link capacitor is regulated by a controller which uses relationship between currents of the DC-link capacitor and that of the traction motor. Experimental results show that the capacitance has been estimated within 2% error bound..