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

摘要

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 and load dump scenarios. The voltage ripple and the current ripple of the DC-link also have an effect on the electromagnetic compatibility (EMC) of the system and on the power losses of the capacitor. Both are affected by the impedance of the overall drive system. This paper shows the influences of the drive system's parasitic impedances on the required DC-link capacitance through a variation of single key parameters. The overall impedance characteristics are analysed and the resonance frequencies are calculated. The effect of the change of impedance on the DC-link voltage ripple and capacitor current ripple is illustrated using a building block system for different car models. Furthermore a calculation method of the voltage ripple based on impedance characteristics is introduced. This underlines the importance of the impedance analysis which allows an accurate dimensioning of the DC-link to save costs, design space and weight.