Optimization of Thickness and Shape of Core Block in Resonator for 7 kW-Class Wireless Power Transfer System for PHEV/EV Charging

Transmitting and receiving resonators for 7 kW-class wireless power transfer/transmission (WPT) systems operating at 85 kHz have been developed for contactless Electric Vehicle (EV) / Plugin Hybrid EV (PHEV) charging. The light weight and small volume of the on-board receiving resonator to be mounted on the vehicle are required attributes. A thickness and a shape of the core in the resonance coil are optimized considering a coil weight, a core loss and a coupling coefficient between the resonators. The coupling coefficient and a coil loss included the core loss of the on-board prototype resonator with the core weight of 4.3 kg and a size of 600 mm by 400 mm are measured for 7 kW-class WPT system. Coil-to-coil power efficiency at the rated transfer power can be estimated with high accuracy by evaluating the core loss. The coil-to-coil efficiency of 93.8% at 160-mm air gap is achieved for the prototype resonator to be mounted on the vehicle.