Optimum Geometries for Wireless Power Transfer Between an Oblong Coil and a Rectangular Coil

The geometry of the coils in a magnetic link and their relative position are crucial for increasing their mutual inductance, which is important for obtaining a higher induced voltage, transferred power, and electrical efficiency. General design guidelines found in the literature point to an increase in mutual inductance by making the coils similar in shape, positioning them as close as possible, and using high-permeability soft-cores to concentrate the flux between them. But these recommendations are often difficult to follow in dynamic inductive wireless power transfer (DIWPT) configurations for vehicular applications. This is mostly due to the necessity of a mechanical clearance between the lane and the vehicle assembly, which creates an “air gap”. Also, unless tracks are used, the lateral movement of a vehicle over a primary coil potentially causes a variation in the induced voltage, which is not adequate to energize the powertrain. Considering these intrinsic problems of DIWPT applications, we developed a few theorems that might facilitate some optimum designs, in the case where rectangular secondary coils are used over oblong primary coils, for two different design targets: (i) maximum induced voltage on the secondary coil and (ii) better insensitivity to the vehicle lateral misalignment on the inductive lane.