Blind-Zone-Free Metal Object Detection System for Wireless EV Charging System Employing Strip Multipolar Detection Coils

A common and urgent problem in electric vehicle (EV) wireless charging technology is the accidental entry of metal objects (MOs) into the charging area where there is no direct physical contact. Eddy currents can be induced in the MOs, generating a large amount of heat and potentially leading to serious consequences such as fire. The current commercially applied MO detection (MOD) technology has the problems of low detection sensitivity, affecting the power transmission magnetic field, and the existence of blind zones. In view of these shortcomings, a MOD system for wireless charging of EVs is proposed in this article. Long strip detection coils are designed and placed above the transmitter coil. Each strip detection coil is composed of 16 unipolar coils having alternating polarities, which can realize decoupling between the detection coil and the transmitter coil and eliminate the interference to the magnetic field of the wireless power transmission system. A third-order Sallen-Key high pass filter and a proportional amplifier circuit are used to improve the sensitivity and accuracy of MOD. Finally, an experimental platform of MOD for EV wireless charging is built, and the proposed system can detect the existence of MOs sensitively and accurately at the location where they may exist.