Method for detecting foreign material, and apparatus and system therefor

A wireless power transmitter, comprising:

• a power transmission unit including at least one coil configured to transmit a power signal having a predetermined strength;
• and
• a controller configured to:
• measure a quality factor and a peak frequency of the at least one coil using the power signal,
• receive reference values including a reference quality factor and a reference peak frequency of a wireless power receiver,
• determine whether or not a foreign object is present in a charging area of the wireless power transmitter based on a comparison of the reference quality factor with the measured quality factor and a comparison of the reference peak frequency with the measured peak frequency,
• control the power transmission unit to transmit response signals indicating a result of the determination, and
• determine whether to continue or stop a wireless charging procedure based on the response signals.

A wireless power receiver, comprising:

• a wireless communication unit configured to communicate with a wireless power transmitter;
• a memory configured to store reference values including a reference quality factor and a reference peak frequency of the wireless power receiver;
• and
• a controller configured to:
• generate first and second foreign object status packets including mode information indicating whether or not information on the reference quality factor and the reference peak frequency are included in the first and second foreign object status packets,
• transmit the first and second foreign object status packets to the wireless power transmitter, and
• receive foreign object detection indicators indicating whether or not a foreign object is present in a charging area of the wireless power transmitter.