Abstract: A system and method to detect the presence of conductive foreign objects for a multi-coil wireless power system is described. A wireless power receiver resonant circuit quality information may be obtained without any costly hardware or termination of power delivery to the power receiver load. The power receiver free-running coil current or voltage may be measured during a very short time window. In this time window, the measurement may be unaffected by transmitter and receiver load due to the transmitter coil disconnection and because the wireless power receiver has sufficient DC-bus capacitance.

Abstract: A power-transmitter-unit comprises a power-transmitting-coil and a resonant-capacitor that define an LC circuit. A controller defines a power-transmission-mode of operation and a foreign-object-detection-mode of operation. In the power-transmission-mode of operation: a power-stage provides a potential-difference across a first-end and a second-end of the LC circuit. In the foreign-object-detection-mode of operation: for a recuperation-time-interval, the power-stage provides a potential-difference across the first-end and the second-end of the LC circuit that has the opposite polarity to the current through the power-transmitting-coil; after expiry of the recuperation-time-interval, the first-end of the LC circuit is connected to the second-end of the LC circuit such that the LC circuit is short-circuited and defines a closed-LC-circuit; and the controller receives measured-signalling that is representative of an operating parameter of the power-transmitter-unit.

Abstract: A system and method to detect the presence of conductive foreign objects for a multi-coil wireless power system is described. A wireless power receiver resonant circuit quality information may be obtained without any costly hardware or termination of power delivery to the power receiver load. The power receiver free-running coil current or voltage may be measured during a very short time window. In this time window, the measurement may be unaffected by transmitter and receiver load due to the transmitter coil disconnection and because the wireless power receiver has sufficient DC-bus capacitance.

Abstract: A power-transmitter-unit comprises a power-transmitting-coil and a resonant-capacitor that define an LC circuit. A controller defines a power-transmission-mode of operation and a foreign-object-detection-mode of operation. In the power-transmission-mode of operation: a power-stage provides a potential-difference across a first-end and a second-end of the LC circuit. In the foreign-object-detection-mode of operation: for a recuperation-time-interval, the power-stage provides a potential-difference across the first-end and the second-end of the LC circuit that has the opposite polarity to the current through the power-transmitting-coil; after expiry of the recuperation-time-interval, the first-end of the LC circuit is connected to the second-end of the LC circuit such that the LC circuit is short-circuited and defines a closed-LC-circuit; and the controller receives measured-signalling that is representative of an operating parameter of the power-transmitter-unit.

Abstract: A power-transmitter-unit includes a power-transmitting-coil for wirelessly providing power to a power-receiver-unit, and a resonant-capacitor connected to the power-transmitting-coil, such that together they define an LC circuit. The LC circuit includes a first-end and a second-end. A controller defines a foreign-object-detection-mode of operation, wherein, in the foreign-object-detection-mode of operation, the first-end of the LC circuit is connected to the second-end of the LC circuit such that the LC circuit is short-circuited and defines a closed-LC-circuit, and the controller is configured to receive a coil-current-signal that is representative of the current through the closed-LC-circuit.