Power transmitter unit
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. The controller further processes the measured-signalling in order to provide an indication of whether or not a foreign object has been detected.
1. A power-transmitter-unit comprising:
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, wherein the LC circuit comprises a first-end and a second-end;
a power-stage for selectively providing power to the LC circuit;
a controller configured to define a power-transmission-mode of operation and a foreign-object-detection-mode of operation, wherein:
in the power-transmission-mode of operation:
the power-stage is configured to provide a potential-difference across the first-end and the second-end of the LC circuit;
in the foreign-object-detection-mode of operation:
for a recuperation-time-interval, the power-stage is configured to provide 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 is configured to receive measured-signalling that is representative of an operating parameter of the power-transmitter-unit;
wherein the controller is further configured to:
process the measured-signalling in order to provide an indication of whether or not a foreign object has been detected.
2. The power-transmitter-unit of claim 1 , wherein, in the power-transmission-mode of operation:
the power-stage is configured to alternately provide a first-potential-difference and a second-potential-difference across the first-end and the second-end of the LC circuit in order to generate current through the power-transmitting-coil.
3. The power-transmitter-unit of claim 2 , wherein, in the foreign-object-detection-mode of operation:
for the recuperation-time-interval, the power-stage is configured to provide the opposite one of the first-potential-difference and the second-potential-difference across the first-end and the second-end of the power-transmitting-coil to the potential-difference that would cause resonance of the current through the power-transmitting-coil.
4. The power-transmitter-unit of claim 1 , wherein the controller is configured to set the recuperation-time-interval based on operational-signalling that is representative of an operating parameter of the power-transmitter-unit obtained during a preceding power-transmission-mode of operation.
5. The power-transmitter-unit of claim 1 , wherein the measured-signalling is representative of an operating parameter of the power-transmitter-unit after expiry of the recuperation-time-interval.
6. The power-transmitter-unit of claim 1 , wherein the measured-signalling is representative of an operating parameter of the closed-LC-circuit.
7. The power-transmitter-unit of claim 1 , wherein:
the measured-signalling comprises a coil-current-signal that is representative of the current through the closed-LC-circuit; and
the controller is configured to:
process the coil-current-signal that was received during the foreign-object-detection-mode of operation, in order to determine the resistance of the closed-LC-circuit; and
provide an indication that a foreign object has been detected if the determined resistance of the closed-LC-circuit is greater than a resistance-threshold value.
8. The power-transmitter-unit of claim 1 , further comprising an ADC configured to provide the measured-signalling as a sequence of digital samples that are representative of an operating parameter of the closed-LC-circuit.
9. The power-transmitter-unit of claim 1 , wherein the controller is configured to apply an auto-regressive modelling algorithm to the measured-signalling in order to provide an indication of whether or not a foreign object has been detected.
10. The power-transmitter-unit of claim 1 , wherein the controller is configured to apply a least squares method to the measured-signalling in order to provide an indication of whether or not a foreign object has been detected.
11. The power-transmitter-unit of claim 1 , wherein the controller is configured to disable the power-transmission-mode of operation if the controller provides an indication that a foreign object has been detected.
12. The power-transmitter-unit of claim 1 , wherein:
the power-transmitter-unit comprises a plurality of power-transmitting-coils for wirelessly providing power to a power-receiver-unit, wherein each power-transmitting-coil is connected to a resonant-capacitor to define an LC circuit, and wherein each LC circuit comprises a first-end and a second-end; and
in the power-transmission-mode of operation:
the power-stage is configured to provide a potential difference across the respective first-ends and second-end of the plurality of LC circuits;
in the foreign-object-detection-mode of operation, for each of the plurality of LC circuits in turn:
for a recuperation-time-interval, the power-stage is configured to provide 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 is configured to receive measured-signalling that is representative of an operating parameter of the power-transmitter-unit;
wherein the controller is further configured to:
process the measured-signalling in order to provide an indication of whether or not a foreign object has been detected.
13. An electronic device comprising the power-transmitter-unit of claim 1 .
14. A method of detecting a foreign object, the method comprising:
in a power-transmission-mode of operation:
providing a potential-difference across a first-end and a second-end of an LC circuit, wherein the LC circuit comprises a resonant-capacitor connected to a power-transmitting-coil;
in a foreign-object-detection-mode of operation:
for a recuperation-time-interval, providing 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, connecting the first-end of the LC circuit to the second-end of the LC circuit such that the LC circuit is short-circuited and defines a closed-LC-circuit; and
receiving measured-signalling that is representative of an operating parameter of the power-transmitter-unit;
processing the measured-signalling in order to provide an indication of whether or not a foreign object has been detected.