Method for detecting foreign material, and apparatus and system therefor

A power transmission method for a wireless power transmitter, the power transmission method comprising:

• receiving, from a wireless power receiver, a foreign object detection (FOD) status packet including information on a reference quality factor or a reference peak frequency;
• determining whether a foreign object is present in a charging area of the wireless power transmitter based on the FOD status packet;
• generating a foreign object detection indicator indicating whether the foreign object is present in the charging area of the wireless power transmitter based on a result of the determination and transmitting the generated foreign object detection indicator to the wireless power receiver,
• 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, and
• wherein all bits of the reservation field are recorded as zero;
• and
• performing a wireless charging procedure with a first power when the foreign object detection indicator indicates that the foreign object is not present in the charging area.