Fourier Analysis and Design of a Shielded 120 kW Inductive Wireless System

High-power inductive wireless power transfer (WPT) systems for electric vehicles are designed to meet specifications, such as stray field, power level, efficiency, misalignment tolerance, and ground clearance. These metrics are all heavily influenced by the coil geometry. This article proposes a coil design method based on the Fourier analysis method (FAM), which is an analytical method for directly designing coil geometries to meet stray field and power level requirements through an optimization of Fourier basis function coefficients. In this work, two 120 kW WPT proof-of-concept demonstrators with low stray field and high efficiency are built from FAM optimization results to validate the models and show the impact of the FAM design process. Experimental validation of the Generation 2 demonstrator at 120 kW output power resulted in a measured dc/dc efficiency of 97.2% at alignment with a 125 mm airgap. At the 120 kW test point, the stray fields 80 cm away from the center of the airgap between the coil assemblies were 3.4 μT(rms) on the X-axis and 3.5 μT(rms) on the Y-axis, much lower than the 27 μT(rms) ICNIRP limit.