A Study of Leakage Magnetic Field Reduction by Active Shielding for Receiver Coil Moving in DWPT Using Air-Core Coils

Leakage magnetic field reduction is one of the challenges for the practical application of DWPTs. It must be reduced because of concerns about its adverse effects on the human body and electronic equipment. In DWPT, the position of the receiver coil changes as the vehicle runs, so a reduction method corresponding to this is necessary. In this paper, the transfer coil installed next to the coil transmitting power to the EV is used as a cancel coil, and the leakage magnetic field is reduced by adjusting the magnitude and phase of the input voltage to the cancel coil according to the position of the receiver coil. The input voltage to the transfer coil is set to the value at which the received power becomes 25 kW. Using SS, LCC-S and Double-LCC as the resonance method, the leakage magnetic field could be reduced to less than the regulated value of 13.8 mA/m in the range from -770 to 800 mm with the center of the transfer coil as the origin. It was also confirmed that the transfer efficiency including the canceling coil can be over 90% for SS and LCC-S, and about 90% for Double-LCC. These were shown using theoretical equations and electromagnetic field analysis using the moment method.

I. Introduction

DWPT (Dynamic Wireless Power Transfer) has attracted attention as a technology to facilitate the transition from internal combustion engine vehicles to electric vehicles, which is one method to solve global environmental problems [1]–[3]. Reasons for the lack of progress in the transition include the shorter range of electric vehicles compared to internal combustion engine vehicles and the time required for recharging, which can be solved by DWPT. There are various challenges to the practical application ofDWPT, the leakage magnetic field problem being one of them. This refers to the magnetic field that leaks into the surroundings during wireless power transfer. It is concerned that leakage magnetic fields may have adverse effects on the human body and electronic equipment, and regulated values have been established by CISPR and ICNIRP. This is an essential technology because DWPT requires nearly 10 times more power transfer than SWPT (Static Wireless Power Transfer).