Metal Object Detection by Monitoring Fifth-Order Harmonic Current of IPT System With Dual Frequency Tuning

A key challenge for safe operation of inductive power transfer (IPT) systems is to detect the presence of metal objects (MOs), particularly when a power receiver (Rx) is misaligned from a power transmitter (Tx) during online charging. This letter proposes a metal object detection (MOD) method by monitoring the fifth-order harmonic current of a dual-frequency IPT system driven by a voltage-fed inverter with square-wave output. While power transfer is maintained by tuning at the fundamental frequency, the Tx circuit is tuned simultaneously at the fifth-order frequency to ease the detection of the fifth-order harmonic current for MOD. The Rx circuit is also fully tuned at the fifth-order frequency, but the fifth order current is completely blocked. With the proposed dual-frequency tuning configuration, the presence of MO causes a significant drop in the fifth-order harmonic current at the Tx side, whereas the Rx behaves as an open circuit with no effect on power transfer. Circuit and magnetic field simulation results show the fifth-order harmonic current presents a unique response to the existence of MO, which is in good agreement with practical measurements. Experimental results demonstrate that at a constant 10 W power output, both nonferrous and ferrous MOs within the Tx charging area can be 100% detected, even when the Rx is misaligned by 50% of the Tx coil radius.