Electrically-powered vehicles such as electric vehicles and hybrid vehicles are of great interest as they are environmentally-friendly vehicles. These vehicles are each mounted with an electric motor generating driving force for the vehicle to travel as well as a rechargeable power storage device storing electric power to be supplied to the electric motor. The hybrid vehicles refer to those including a vehicle mounted with an internal combustion engine as a source of motive power in addition to the electric motor, and a vehicle mounted with a fuel cell as a source of DC (direct current) electric power for driving the vehicle in addition to the power storage device.
It is known that some hybrid vehicles have a power storage device mounted on the vehicle and chargeable from a power supply external to the vehicle, like the electric vehicles. For example, a so-called “plug-in hybrid vehicle” is known that has a power storage device chargeable from a power supply of an ordinary household by connecting a power supply outlet provided at the house and a charging inlet provided at the vehicle by means of a charging cable.
As for the way to transmit electric power, wireless power transmission without using power supply cord and power transmission cable has been of interest in recent years. Three techniques are known as predominant wireless power transmission techniques. These techniques are power transmission by means of electromagnetic induction, power transmission by means of electromagnetic wave, and power transmission by means of a resonance method.
Among them, the resonance method is a noncontact power transmission technique, with which a pair of resonators (a pair of self-resonant coils for example) is caused to resonate in an electromagnetic field (near field) and electric power is transmitted through the electromagnetic field. With the resonance method, a large amount of electric power of a few kW can be transmitted over a relatively long distance (a few meters for example) (see Non-Patent Document 1).    Patent Document 1: Japanese Patent Laying-Open No, 10-257681    Patent Document 2: Japanese Patent Laying-Open No. 2006-320079    Patent Document 3: International Patent Publication No. 2007/008646    Non-Patent Document 1: Andre Kurs et al., “Wireless Power Transfer via Strongly Coupled Magnetic Resonances” (online), Jul. 6, 2007, Science, Vol. 317, pp. 83-86 (searched Sep. 12, 2007), on the Internet    <URL:http://www.sciencemag.org/cgi/reprint/317/5834/83.pdf>
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