Non-uniform Spacing of Ferrite Bars for Optimizing a Solenoid-based Wireless Electric Vehicle Charger with Automatic Self-Alignment

This paper presents the design of a dual-coil charging pad for Wireless Power Transfer (WPT) in Electric Vehicles (EV). An electro-magnetic coil, denoted as the DC coil, generates a magnetic force that horizontally aligns a linear-slider-mounted transmitter pad to the receiver pad. A solenoid-based coil, denoted as the ac coil, is capable of 5kW WPT, which is performed only after the self-alignment of the pads. Two areas of optimization for the solenoid-based wireless charger are presented: optimum ferrite bar spacing and shield design. By using copper shields composed of a continuous sheet instead of multiple pieces connected with tape, the simulated eddy current loss is reduced by 29% while minimizing leakage flux from the ac coil. The optimum ferrite bar spacing is verified on a prototype of the dual-coil charging pad and allows the power capability to increase from 3.7 kW to 5 kW, without additional ferrite bars while achieving a peak DC-dc efficiency of 90.1%. The prototype of the DC coil generates a peak magnetic force of 3.51 N while also achieving a wide horizontal misalignment correction range of up to 240 mm.