Wireless inductive power transfer

A power transmitter for a wireless power transfer system including a power receiver arranged to receive power from the power transmitter via a wireless inductive power transfer signal generated by the power transmitter, and to transmit a standby mode exit request by changing a loading of a communication inductor;

• the power transmitter comprising:
• the communication inductor for communicating with the power receiver;
• a mode controller for controlling the power transmitter to operate in a standby mode wherein a presence of the power receiver is detected but no power transfer signal is generated;
• a detector for detecting an impedance change of the communication inductor;
• and wherein the mode controller is arranged to initiate a transition from the standby mode to a power transfer mode in response to the detector detecting the impedance change;
• wherein the communication inductor is part of a resonance circuit and the detector is arranged to apply an excitation signal comprising at least one excitation causing oscillations to the resonance circuit exceeding a duration of the excitation of the excitation signal, and to detect the impedance change from a measurement of at least one of a communication inductor voltage and a communication inductor current, wherein the measurement is performed with a time offset relative to a time of the excitation.

A method of operation for a wireless power transfer system including a power transmitter arranged to provide a power transfer to a power receiver via a wireless inductive power transfer signal generated by the power transmitter,

• the method comprising:
• the power transmitter operating in a standby mode wherein a presence of the power receiver is detected but no power transfer signal is generated;
• the power receiver transmitting a standby mode exit request to the power transmitter by changing a loading of a communication inductor of the power transmitter;
• the power transmitter detecting an impedance change of the communication inductor;
• and
• the power transmitter initiating a transition from the standby mode to a power transfer mode in response to the detection of the impedance change;
• wherein the communication inductor is part of a resonance circuit, the method further comprises the power transmitter applying an excitation signal comprising at least one excitation causing oscillations to the resonance circuit exceeding a duration of the excitation of the excitation signal, and the detection of the impedance change is from a measurement of at least one of a communication inductor voltage and a communication inductor current, wherein the measurement is performed with a time offset relative to a time of the excitation.

A method of operation for a power transmitter for a wireless power transfer system including a power receiver arranged to receive power from the power transmitter via a wireless inductive power transfer signal generated by the power transmitter, and to transmit a standby mode exit request by changing a loading of a communication inductor;

• the method comprising:
• controlling the power transmitter to operate in a standby mode wherein a presence of the power receiver is detected but no power transfer signal is generated;
• detecting an impedance change of the communication inductor;
• and
• initiating a transition from the standby mode to a power transfer mode in response to the detection of the impedance change;
• wherein the communication inductor is part of a resonance circuit, the method further comprises the power transmitter applying an excitation signal comprising at least one excitation causing oscillations to the resonance circuit exceeding a duration of the excitation of the excitation signal, and the detection of the impedance change is from a measurement of at least one of a communication inductor voltage and a communication inductor current, wherein the measurement is performed with a time offset relative to a time of the excitation.