The present disclosure relates to a foreign object detector, a method of detecting a foreign object, and a non-contact charging system.
In recent years, wireless power transmission systems (i.e., non-contact charging systems) have been, and are being, developed to charge, for example, electric vehicles via a non-contact method. In each wireless power transmission system, a transmitting coil and an RF oscillation source are provided for a charger, and a receiving coil is provided for an electric vehicle. Some wireless power transmission systems using an electromagnetic induction method enable high-efficiency non-contact power transmission.
Such a wireless power transmission system using the electromagnetic induction method is designed to transmit a large quantity of electric power. Therefore, if a metallic foreign object enters the gap between its transmitting and receiving coils and/or its environment, there is a risk that the system would generate heat. In view of this consideration, it is thus important, for safety reasons, to detect such a metallic foreign object before or during charging.
As a conventional method of detecting a foreign object in a wireless power transmission system, there is a method of detecting a change in the inductance of a detection coil to be caused by electromagnetic induction between the metal and the detection coil (see, e.g., Japanese Unexamined Patent Publication No. 2012-16125).