Conventionally, as one example of a system for charging a battery of an electric vehicle or a plug-in hybrid car, there has been developing a method that transfers power to the vehicle in contactless manner by using electromagnetic induction, as illustrated in FIG. 8. In particular, the method transfers power from a primary transformer (power transmitting transformer) 31 provided on the ground to a secondary transformer (power receiving transformer) 33 of a power transfer transformer 30 of a contactless power transfer system installed on a floor of the vehicle.
The plug-in hybrid car to be charged includes: an engine 54 and a motor 53 as a driving source; a secondary battery 51 that is a power source for the motor; and an inverter 52 that converts a direct current of the secondary battery 51 to an alternative current, and supplies the alternative current to the motor.
The contactless power transfer system includes, on the ground side: a variable voltage rectifier 10 that converts an alternative current of the commercial power source to a direct current, and changes the voltage thereof; an inverter 20 that generates a high-frequency alternative current from the direct current; a power transmitting transformer 31 that is one of the contactless power transfer transformer 30; and a primary series capacitor 32 that is connected to the power transmission transformer 31 in series.
On the other hand, the contactless power transfer transformer 30 includes, on the vehicle side: a power receiving transformer 33 that is other one of the contactless power transfer transformer 30; a rectifier 35 that converts the alternative current to the direct current for the secondary battery; and a secondary parallel resonance capacitor 34 that is connected between the power receiving transformer 33 and the rectifier 35 in parallel.
FIG. 9 illustrates one example of a circuit diagram of the contactless power transfer system.
For such a system, the power transfer efficiency is desired not to be largely decreased even in the case when a stop position of the vehicle is misaligned and thereby the power transmitting transformer 31 and the power receiving transformer 33 do not oppose each other or in the case when a gap (spacing) between the power transmitting transformer 31 and the power receiving transformer 33 is changed.
Patent Literature 1 described below discloses a contactless power transfer transformer that allows large position deviation or large change in the gap and that can be configured in a small size. As illustrated in FIG. 10A to 10F, the contactless power transfer transformer is configured by an H-shaped ferrite core 40. Portions of the ferrite core 40 parallel to each other at the both sides of the H-shape is provided as magnetic pole portions 41, 42. A portion corresponding to the horizontal pole of the H-shape, i.e., a winding wire core member 43 (a portion connecting between the magnetic pole portions) is wound around by an electric wire 50. FIG. 10A is a state in which the electric wire 50 is wound around the ferrite core 40, and FIG. 10D is a state in which the electric wire 50 is not wound around the ferrite core 40. Further, FIG. 10B is a cross-sectional view taken along a line A-A of FIG. 10A, and FIG. 10C is a cross-sectional diagram taken along line B-B of FIG. 10A. Similarly, FIG. 10E is a cross-sectional view taken along a line A-A of FIG. 10D, and FIG. 10F is a cross-sectional view taken along line B-B of FIG. 10D.
According to the contactless power transfer transformer that uses the H-shape core, the following properties which satisfies utility can be obtained when the power transfer of 3 kW is performed by the power transmitting transformer and the power receiving transformer opposing each other with a standard gap length of 70 mm. That is, the efficiency of the transformer is 95%, the allowable position deviation in the left and right direction (y direction in FIG. 10A) is ±150 mm, the allowable position deviation in the front and back direction is ±60 mm, and the efficiency at which the standard gap length is increased to 100 mm is 92%.
Furthermore, as the contactless power transfer transformer that uses the H-shape core, there exists a prototype that can perform fast charging at large capacity of greater than or equal to 10 kW.