A Three-Phase Wireless-Power-Transfer System for Online Electric Vehicles With Reduction of Leakage Magnetic Fields

Wireless charging of electric vehicles based on wireless power transfer (WPT) has become increasingly popular in recent years. However, a leakage electromagnetic field (EMF) that affects other electronic devices or the human body is inevitably generated from the coils of a WPT system, and requirements regarding the suppression of the leakage EMF are increasing. In this paper, we propose a novel three-phase power line in a WPT system for the reduction of the leakage EMF. The proposed structure employs six power lines to reduce the leakage magnetic flux. This structure is compared with conventional power line structures with respect to induced voltage and magnetic field distribution. We also present analytical solutions of the EMF for the proposed and conventional power line structures. These solutions are then compared with numerical solutions using 3-D finite-element analysis and good agreement is demonstrated. The results of the numerical analysis indicate that the proposed power line can significantly reduce the leakage magnetic field from a WPT system. For verification, the proposed and conventional power lines are implemented and the EMFs are measured. A strong correlation between the numerical and experimental results is exhibited.