Common Mode Noise Analysis for Inductive Power Transfer System Based on Distributed Stray Capacitance Model

Abstract

This article reveals the significant stray capacitances in inductive power transfer (IPT) coil, and offers two methods for modeling the stray capacitance effect: concentrated model and distributed model. Both analytic formulas and FEM simulation are introduced to estimate the value of parasitic capacitances, and experimental measurements on an 11 kW IPT coil prototype are conducted to verify the correctness of both methods. The common-mode noise propagation circuit of the IPT system is derived and simulated based on these two models. The results show that parasitic capacitance between Litz wire winding and shielding metal on the transmitter side plays a dominant role in CM noise propagation and the distributed model has higher fidelity because of its asymmetric structure. Besides, to mitigate conductive CM noise, an EMI filter, and HF isolation transformer are introduced. Finally, the conductive EMI tests are performed in an 11kW IPT prototype. The experimental results validate the accuracy of the proposed CM noise model with stray capacitances of the IPT coil. And the combination of EMI filter and HF isolation transformer can suppress CM noise greatly and render the CM noise spectrum below the CISPR 32 Class-B limit.