Magnetic Shield Design for the Double-D Coil-Based Wireless Charging System

In this study, magnetic field emission (MFE) of the high-power double-D (DD) coil-based wireless charging system is investigated and a shielding technique is proposed. The MFE pattern produced by the DD coils is significantly different from the MFE of the unipolar (e.g., circular, square, or rectangular) coils, and the traditional aluminum shield does not suppress the MFE from the DD coils. This study shows that a conventional aluminum shield increases the MFE, and a magnetic shield effectively suppresses the MFE of the DD coils. Therefore, a magnetic shield consisting of high-permeability magnetic material, such as ferrites, nanocrystalline, etc., is proposed for the DD pads. The shielding effectiveness of the proposed shield is evaluated through finite-element analysis and verified through experiments. An 11-kW DD coil-based wireless charging system was used to test the proposed shielding technique. The experimental results show that a traditional aluminum shield increased the MFE by 29.8%, and the proposed magnetic shield suppressed the MFE by 50.5%.

I. Introduction

Wireless charging system (WCS) is one of the most promising technologies being investigated to enhance the convenience of charging electric vehicles (EVs) [1]–[6] . Improvement in the efficiency and power density of WCSs along with the rapid growth of the EV market—which benefits from fast and convenient charging—have resulted in significant academic and industrial research attention on developing WCSs for high-power EV charging [7], [8]. However, for high-power EV charging, the WCSs are highly prone to produce a significant level of electromagnetic field (EMF) emissions, causing serious health and safety concerns, if the couplers and shields are not designed properly [9]–[14].