Power source, wireless power transfer system, and positional information calculation method of power receiver

A wireless power transfer system which wirelessly transfers power from a power source to a power receiver using one of magnetic field resonance and electric field resonance, wherein

• the power source comprising:
• a power receiver detection unit, which is provided near a power supply zone used by at least two power source coils, and configured to detect the power receiver which is brought into proximity thereto or contact therewith;
• a power transfer control unit configured to control the power source coil;
• and
• a first communication circuit unit configured to perform out-band communication, using a frequency different from that of transferring power from the power source to the power receive, with the power receiver, and
• the power receiver comprising:
• a reference position detection unit configured to detect a position where the power receiver is in proximity to or contact with the power receiver detection unit as a reference position;
• a first sensor configured to calculate a distance across which the power receiver moves from the reference position;
• a power reception control unit configured to calculate first positional information from the reference position, based on output of the first sensor;
• and
• a second communication circuit unit configured to perform out-band communication with the power source, wherein
• the power transfer control unit is configured to
• control the power source coil based on the first positional information, at start of power transfer from the power source to the power receiver, and
• control the power source coil based on second positional information of the power receiver calculated from an efficiency obtained via the first communication circuit unit and the second communication circuit unit, after the start of power transfer from the power source to the power receiver.