Wireless power transmission system

A wireless power transmission system for wirelessly transmitting electric power from a power feeding device to a power receiving device, wherein,

• the power feeding device comprises:
• a power feeding coil which receives an electric power to generate an AC magnetic field;
• an inverter for providing an alternating-current power with a predetermined driving frequency to the power feeding coil;
• a current detection circuit for detecting a peak value of an alternating current flowing in the power feeding coil;
• a controller for controlling the alternating current flowing in the power feeding coil;
• and a wireless receiving module,
• the power receiving device comprises:
• a power receiving coil for receiving electric power wirelessly via the AC magnetic field;
• a power receiving side resonance capacitor which constitutes a power receiving side LC resonance circuit together with the power receiving coil;
• a rectifier for rectifying the electric power received by the power receiving coil;
• a voltage detection circuit which detects the output voltage of the rectifier;
• and a wireless transmission module which transmits the output voltage value detected by the voltage detection circuit to the wireless receiving module,
• the controller adjusts the driving frequency to substantially conform to a resonance frequency of the power receiving side LC resonance circuit;
• controls the alternating current flowing in the power feeding coil to be constant;
• performs a small power feeding using at least two different values of the output voltage values, during which the output voltage value received by the wireless receiving module becomes constant, with a transmission power lower than that of a main power feeding before the main power feeding;
• and controls the alternating current flowing in the power feeding coil based on the correlation between the different output voltage values and the different alternating current peak values corresponding to the different output voltage values, respectively, detected by the current detection circuit.