Foreign object detection method and apparatus, and wireless charging system

A wireless charging system, comprising:

• a power transmitting apparatus, and
• a foreign object detection apparatus comprising:
• a coil array comprising at least one coil group, each coil group comprises four detection coils separately wound into a rectangle shape, the detection coils in the coil array are arranged in a matrix with even quantities of rows and columns, four detection coils in the coil array whose locations are symmetrical to each other are located in one coil group, and each detection coil is electrically connected to a foreign object detection circuit, wherein the coil array is divided into four quadrants based on a row center line and a column center line of the coil array, wherein detection coils in a same quadrant have a same wiring structure wound clockwise or counterclockwise, and wiring structures of the detection coils in adjacent quadrants are symmetrical to each other relative to a center line between the adjacent quadrants, and
• the foreign object detection circuit comprising a signal obtaining unit and a signal processing unit, and the signal processing unit is electrically connected to the signal obtaining unit, wherein
• the signal obtaining unit is configured to obtain, under control by the signal processing unit, an induction signal generated by each detection coil in each coil group, and wherein
• the signal processing unit is configured to:
• determine an abnormal-value threshold of each coil group based on induction signals of each coil group obtained in a first time period, and
• detect, based on the abnormal-value threshold and the induction signals of each coil group, whether there is a foreign object in a detection region corresponding to the coil array, wherein the first time period is a preset time period after the induction signals start to be obtained.