Dual-Purpose Nonoverlapping Coil Sets as Metal Object and Vehicle Position Detections for Wireless Stationary EV Chargers

Abstract

For commercialization of wireless stationary electric vehicles (EV) chargers, metal object detection (MOD) on a power supply coil and detection of position (DoP) of EVs are needed. In this paper, dual-purpose nonoverlapping coil sets for both MOD and DoP, which detect a variation of magnetic flux on the power supply coil, are newly proposed, where the proposed MOD and DoP methods make no contribution to any power losses. The existence of metal objects on the power supply coil is determined by an induced voltage difference of the nonoverlapping coil sets, whereas the position of the EV is determined by an induced voltage of the nonoverlapping coil sets. A sensing circuit, which has a variable resistor that is different from the conventional overlapping coil for MOD, can make the induced voltage difference zero even when the magnetic flux distribution is distorted by moving the pick-up coil. The proposed nonoverlapping coil sets with the sensing circuit have been demonstrated by simulations and experiments. When metallic coins and aluminum sheets are located on the power supply coil, the induced voltage difference of the coil sets, which is ideally zero without metal objects, significantly increases to 62.8 and 450 mV, respectively, which is more than ten times the value without metal objects throughout experiments. In addition, when the pick-up coil approaches the power supply coil, induced voltage of each coil set increased roughly 1.6 times at 10 cm air gap.