Patent attributes
A power transmission apparatus includes a primary coil connected to an AC source; a primary resonance coil configured to receive power from the primary coil; a secondary resonance coil configured to receive power from the primary resonance coil by magnetic field resonance occurred between the primary resonance coil and the secondary resonance coil; a secondary coil configured to receive power from the secondary resonance coil; a phase difference detector detect a phase difference between a phase of voltage supplied to the primary resonance coil and a phase of current flowing through the primary resonance coil; a variable capacitor provided on the primary resonance coil; and a determination part determining a coupling degree between the primary resonance coil and the secondary resonance coil based on a change degree of the phase difference relative to a change amount of capacitance when the capacitance of the variable capacitor changes.
