Analyzing and reducing common mode noise in high power inductive power transfer systems for electric vehicles using precise balance technique

In inductive power transfer (IPT) charging systems for electric vehicles (EVs), shielding metals are commonly used to reduce electromagnetic field (EMF) radiation emitted by the coils. Nevertheless, these components also introduce additional common mode (CM) noise to the system and affect the electromagnetic compatibility (EMC) performance. To mitigate the impact of the CM noise, this paper investigates the asymmetric character of CM impedance of the IPT coils and proposes a distributed circuit model to reflect the stray capacitances of the IPT coils. A comprehensive analysis is conducted to determine the CM impedance and a complete CM noise model is subsequently derived for the IPT system. Based on the novel CM noise model, a balance technique is built on a symmetric compensation circuit topology, without the need for additional hardware. The balance technique is provided to ensure compliance with the CISPR 22 standard for CM noise. An 11 kW IPT prototype with the LCC (Inductor-Capacitor-Capacitor) compensation network has been implemented and experiments have been conducted. At low frequency (150 kHz to 5 MHz), the conductive CM noise is reduced by 5 dB; at high frequency (5 MHz to 30 MHz), is reduced by 13 dB, which validates the effectiveness of the proposed balance technique.