Abstract
The objective of this paper is to study a 22 kW high-power wireless power transfer (WPT) system for battery charging in electric vehicles (EVs). The proposed WPT system consists of a three-phase half-bridge LC–LC (i.e., primary LC/secondary LC) resonant power converter and a three-phase sandwich wound coil set (transmitter, Tx; receiver, Rx). To transfer power effectively with a 250 mm air gap, the WPT system uses three-phase, sandwich-wound Tx/Rx coils to minimize the magnetic flux leakage effect and increase the power transfer efficiency (PTE). Furthermore, the relationship of the coupling coefficient between the Tx/Rx coils is complicated, as the coupling coefficient is not only dominated by the coupling strength of the primary and secondary sides but also relates to the primary or secondary three-phase magnetic coupling effects. In order to analyze the proposed three-phase WPT system, a detailed equivalent circuit model is derived for a better understanding. To give a design reference, a novel coil design method that can achieve high conversion efficiency for a high-power WPT system was developed based on a simulation-assisted design procedure. A pair of magnetically coupled Tx and Rx coils and the circuit parameters of the three-phase half-bridge LC–LC resonant converter for a 22 kW WPT system are adjusted through PSIM and CST STUDIO SUITE™ simulation to execute the derivation of the design formulas. Finally, the system achieved a PTE of 93.47% at an 85 kHz operating frequency with a 170 mm air gap between the coils. The results verify the feasibility of a simulation-assisted design in which the developed coils can comply with a high-power and high-efficiency WPT system in addition to a size reduction.