Metal Object Detection Circuit with Non-overlapped Coils for Wireless EV Chargers

In the inductive power transfer (IPT) system operation, overheating of metal objects caused by eddy current may cause ignition, resulting in fire or damages to the equipment. Therefore, a metal object detection (MOD) circuit with non-overlapped coils to ensure safe operation of a wireless EV chargers is proposed in this paper. The proposed MOD circuit is composed of a variable resistor, a low pass filter, and a precision rectifier with amplification for accurate data acquisition. Influence of metal object under alternating magnetic field is described with respect to various thickness and types of metal objects. The proposed MOD circuit was experimentally verified using three non-overlapped coils and a 4cm x 4cm metal object, where its output voltage was changed from 200 mV to 1V. The MOD circuit can detect multiple metal objects at the same time and is suitable for high power wireless EV chargers.