Wireless power feeding for electric vehicles and plug-in hybrid vehicles is expected to be put into practical use around 2015. Every company and organization involved in the development is undergoing a fierce competition, and the development of wireless power feeding accelerates lately.
Researchers from Saitama University and Technova developed a technology to the interactive electric transmission between coils on a vehicle and those on a house. In the experiment, they transmitted electricity of 3 kW at 50 kHz frequency for a distance of 16 cm between vehicle and house and achieved about 93% efficiency in both ways. Interactive electricity transmission allows transmitting electricity stored in a vehicle back to a house and makes it usable as a power source in a disaster.
Yoichi Hori of the University of Tokyo is studying a technology to bury multiple transmission coils in the ground to relay electricity for power feeding of vehicles traveling between the transmission coils. Electromagnetic waves are liable to change when multiple coils exist between the transmitter and receiver, and it is hard to feed power exactly to the destination. His research team successfully developed a method to calculate the optimal current to be transmitted to the transmission coil using data from vehicles like voltage and current. With this method, it is possible to distribute power as needed. Showa Aircraft and Nissan are conducting the experiment to drive a carriage on the road in which coils are buried. They plan to achieve transmission efficiency of more than 80% in an interval of more than 20 cm between coils. Charging your vehicle while you are driving it naturally decreases the frequency to visit a station for charging.
Broadband Wireless Forum participated by wireless carriers will publish a new guideline on wireless power feeding on May 31. The guideline will discuss the influence of wireless power feeding on human body, though equipment with an output of several kilowatts for power feeding to EVs is not subject to the guideline at the present stage. Influence on human body is very important in addition to deregulation because electromagnetic wave at a frequency higher than 10 kHz is subject to the Radio Wave Law.
A demonstration of wireless power feeding