Electromagnetically-coupled state detection circuit, power transmission apparatus, contactless power transmission system, and electromagnetically-coupled state detection method

A power transmission apparatus comprising:

• a power transmission circuit including a primary side coil;
• and
• detection circuitry,
• wherein, the detection circuitry includes circuitry to
• measure a primary side Q value of the power transmission circuit including the primary side coil,
• generate a first power transmission efficiency value for the power transmission circuit,
• generate a corrected power transmission efficiency value based on the primary side Q value of the primary side coil, and
• determine a state of electromagnetic coupling with the secondary side coil with a conductor based on the corrected power transmission efficiency value by comparing the corrected power transmission efficiency with a predetermined threshold power transmission efficiency value.

A contactless power transmission system comprising:

• a power transmission apparatus that wirelessly transmits power;
• and
• a power receiving apparatus that receives the power from the power transmission apparatus,
• wherein the power receiving apparatus includes
• a secondary side coil electromagnetically coupled with a primary side coil of the power transmission apparatus, and
• a secondary side communication unit that communicates with the power transmission apparatus, and
• wherein the power transmission apparatus includes
• the primary side coil electromagnetically coupled with the secondary side coil of the power receiving apparatus,
• a primary side communication unit that communicates with the power receiving apparatus,
• a detection unit that measures a primary side Q value of a circuit containing the primary side coil and power transmission efficiency to the secondary side coil based on information about the power receiving apparatus received by the primary side communication unit, corrects the power transmission efficiency based on the Q value of the primary side coil, and detects a state of electromagnetic coupling with the secondary side coil based on an obtained corrected value of the power transmission efficiency, and
• determines the state of electromagnetic coupling with the secondary side coil by comparing the corrected value calculated by the corrected value operation unit with a threshold set based on a corrected value measured in advance when no conductor is present near the primary side coil.