Minimizing Material Usage for Efficient and Compact Coil in Wireless Charging System of Electric Vehicles

For the wireless charging system (WCS), excessive material usage in coils is a major barrier toward their commercialization. In this article, a sequential design method is proposed to minimize material efforts. First, Pareto-based optimization is executed to determine the size of coil, ferrite usage, and litz wire's gauge, which govern the rough geometry. Then strand number, winding geometry, and ferrite placement are studied, respectively, to further reduce the amount of copper while achieving compromise between losses and shielding effect. The proposed concept provides detailed optimization procedure for material reduction and cost evaluation. It can be principally extended to varied coil geometries and power levels. Two types of coils are compared and verified on a scale-down 6.6-kW WCS prototype, where the dc-dc efficiency reaches nearly 95.6% across the air gap of 150 mm under aligned position, with a coil diameter of 450 mm and a weight of 2.63 kg. The total copper and ferrite usage shows noticeable reduction compared with previous ones. The results demonstrate how the proposed concept can improve material utilization without degrading major metrics.