Kenichirou Ogawa

EMI reduction technology in 85 kHz band 44 kW wireless power transfer system for rapid contactless charging of electric bus

A 44 kW wireless power transfer (WPT) system is being developed for rapid contactless charging in an electric bus in the 85 kHz band, the candidate frequency for a wireless charging system for light-duty vehicles that is currently undergoing standardization. For field operation of this WPT system using the 85 kHz band in Japan, permission for use as industrial facilities emitting radio waves is required under the Radio Act. A two-channel WPT system with currents of opposite phase in the two transmit pads of the channels is introduced to reduce radiated emissions to within the Radio Act limits of electromagnetic radiation disturbance by cancelling the emission from each channel. Then, the diagonal placement of the transmit pads for the two channels is proposed to avoid the interference between the two channels where the interference couplings become null. Finally, the measured emission of the 44 kW WPT system in a 10 m anechoic chamber is shown.

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.

Design method for low radiated emission of 85 kHz band 44 kW rapid charger for electric bus

Wireless charging technology for heavy-duty vehicles, such as electric buses, has been actively investigated with a view to accelerating deployment of an important form of eco-friendly transportation. We have been developing a wireless power transfer (WPT) system for rapid charging of electric buses. Most of the performance targets were achieved: the maximum electric power received was 44 kW or more, the maximum misalignment tolerance of the transmit and the receive charging pads was +/−10 cm or more, and the radiated emission was reduced to within the limits in accordance with the Radio Act. This paper presents a design method for low radiated emission, and the evaluation of the WPT system.