Understanding conducted emissions from an automotive inverter using a common-mode model

This contribution presents results from an investigation into conducted emissions of an automotive inverter in a component level EMC test setup with unshielded cables. The primary goal of the investigation is to develop a profound understanding of the shape of the disturbance voltage´s frequency spectrum at the line impedance stabilization network. Complying with that objective, common-mode currents are identified as the dominating noise currents, especially at the operating point of the inverter representing the worst case scenario regarding EMC performance. To support this conclusion, an AC simulation of a single-phase common-mode equivalent circuit of the system is presented. The resonances occurring in the noise spectrum and its overall shape are explained by the simulation within the frequency range of 100 kHz to 110 MHz. In addition, CY capacitors are used as common-mode filter elements. Based on the validated simulation model, the influence of the filter capacitors and their parasitic inductances are investigated.