Method for detecting foreign material, and apparatus and system therefor

A wireless power transmitter that transmits power to a wireless powerreceiver, the wireless power transmitter comprising:

• a wireless communication unit configured to communicate with the wireless power receiver;
• and
• a controller,
• wherein the wireless communication unit receives a foreign object detection (FOD) status packet from the wireless power receiver,
• wherein the controller determines whether a foreign object is present in a charging area of the wireless power transmitter on the basis of the FOD status packet,
• wherein the wireless communication unit transmits, to the wireless power receiver, a foreign object detection indicator indicating whether the foreign object is present in the charging area of the wireless power transmitter on the basis of a result of the determination,
• wherein the FOD status packet includes information on a reference quality factor or a reference peak frequency,
• wherein the FOD status packet has a length of two bytes,
• wherein one byte of the FOD status packet includes a six-bit reservation field and a two- bit mode field,
• wherein all bits of the reservation field are recorded as zero, and
• wherein when the foreign object detection indicator indicates that the foreign object is not present in the charging area, the controller is configured to perform a wireless charging procedure with a first power.