Contribution to the Coupling Behavior Analysis of WPT Systems for Electric Vehicles with Flush Ground and Buried Primary Side Mounting

This paper contributes to the coupling behavior analysis of stationary wireless power transfer systems for electric vehicles with flush ground or buried primary side mounting. First, the flux linkage of inductively coupled air coils is derived analytically considering rectangular coil shapes and the air gap. From this, the fundamental correlation between the coupling factor, air gap, and the coil size is examined. Essentially, the flux linkage is defined by the geometrical constraints and, depending on the air gap, can be modified within certain boundaries through the design freedom of the primary side. However, there is a pareto front that limits the maximum coupling. The analytical conclusions are verified by a Finite-Element-Analysis with reference to the SAE J2954 WPT3/Z3 secondary. Finally, a proposal for an optimized active material mass design is discussed.