An Investigation of the Parasitic Impedance on the DC-Link Capacitor of EV Drive Inverters

Inhalt:
The DC-link capacitor is a key component in electric vehicle drive systems. Main dimensioning criteria are the DC-link voltage ripple, the DC-link capacitor current ripple andload dump scenarios. The voltage ripple and the current ripple ofthe DC-link also have an effect on the electromagneticcompatibility (EMC) of the system and on the power losses of thecapacitor. Both are affected by the impedance of the overall drivesystem. This paper shows the influences of the drive system’s parasiticimpedances on the required DC-link capacitance through avariation of single key parameters. The overall impedancecharacteristics are analysed and the resonance frequencies arecalculated. The effect of the change of impedance on the DC-linkvoltage ripple and capacitor current ripple is illustrated using abuilding block system for different car models. Furthermore acalculation method of the voltage ripple based on impedancecharacteristics is introduced. This underlines the importance ofthe impedance analysis which allows an accurate dimensioning ofthe DC-link to save costs, design space and weight.