Mode Conversion and Structure Optimization of Quadrature Coils for Electric Vehicles Wireless Power Transfer

With the rapid growth of the electric vehicles (EVs) market all over the world, wireless power transfer (WPT), as an emerging way of charging batteries, has drawn the attention of researchers, manufactures, and customers recently. Various magnetic coupler configurations, which are essential in WPT systems, have been proposed and analyzed. However, the misalignment tolerances of the existing magnetic couplers are pretty small, which results in a remarkable decrease in the transmission power and efficiency when there is misalignment between two coupling coils. In order to solve this problem, novel quadrature coils and a converting circuit are proposed, which could adjust the coupler structure according to the relative position of the coils on both sides so that the transmission power and efficiency are optimal. The structure of quadrature coils is first optimized with a three-dimensional finite element analysis (3-D FEA) tool ANSYS MAXWELL. On the basis of the optimized parameters, a 3.5 kW WPT experiment platform is constructed. When the horizontal misalignment reaches 150 mm, the input and output power is 2.256 kW and 2.126 kW respectively, thus an efficiency of 94.22% is achieved. The experimental results verify the correctness of the theoretical analysis.