Inductive wireless power transfer with synchronized power measurement

An inductive wireless power receiver comprising:

• a secondary coil, wherein the secondary coil is arranged to receive the inductive wireless power signal,
• a power modulation and demodulation circuit, wherein the power modulation and demodulation circuit modulates and demodulates the inductive wireless power signal,
• a power measurement circuit, wherein the power measurement circuit determines the amount of inductive wireless power received by the power receiver,
• and a communication and control unit,
• wherein the communication and control circuit controls the power modulation and demodulation unit to communicate with the inductive wireless power transmitter, in an allocated time slot of a plurality of communication time slots present in repeating communication frames,
• wherein the communication time slots are allocated and coordinated by the inductive wireless power transmitter,
• wherein the communication and control circuit receives from the inductive wireless power transmitter an announcement of an allocated power measurement time slot for synchronised power measurements,
• wherein the communication and control circuit activates the power measurement unit to determine an amount of inductive power received from the power transmitter during the power measurement time slot,
• wherein the communication and control circuit sends to the wireless power transmitter a message indicating the amount of inductive power received in the allocated time slot after the power measurement time slot,
• wherein the wireless power transmitter detects foreign objects based on a calculated amount of power lost in the wireless power transfer system based on a cumulative amount of inductive power received from the inductive wireless power receiver and the at least one further inductive wireless power receiver.

A method of detecting foreign objects by determining a power loss in an inductive wireless power transfer system comprising an inductive wireless power transmitter for transmitting an inductive wireless power signal and at least two inductive wireless power receivers for receiving the inductive wireless power signal,

• wherein the power transmitter and the power receivers are arranged to communicate using modulation and demodulation of the inductive wireless power signal,
• where the communication is proportioned in a plurality of time slots and coordinated by the power transmitter,
• the method comprising:
• allocating, by the power transmitter, a different time slot to each of the at least two inductive wireless power receivers for sending messages to the power transmitter,
• allocating, by the power transmitter, a synchronised power measurement time slot and sending a message to the power receivers announcing the synchronised power measurement time slot,
• measuring, by the power transmitter, during the power measurement time slot, the inductive wireless power transmitted by the power transmitter,
• measuring, by each of the power receivers, during the power measurement time slot, an inductive wireless power received by that power receiver,
• sending, by each of the power receivers, in each allocated time slot after the power measurement time slot, a message to the power transmitter indicating the measured power received by that power receiver,
• calculating, by the power transmitter, the power loss from the measured inductive wireless power transmitted by the power transmitter and the measured inductive wireless powers received by each of the power receivers,
• reducing, by the power transmitter, the power of the inductive wireless power signal if the calculated power loss exceeds a threshold value.

A method of detecting foreign objects by determining a power loss in an inductive wireless power transmitter for transmitting an inductive wireless power signal to at least two inductive wireless power receivers for receiving the inductive wireless power signal,

• wherein the power transmitter is arranged to communicate with the power receivers using modulation and demodulation of the inductive wireless power signal,
• wherein the communication is proportioned in time slots and coordinated by the power transmitter,
• the method comprising allocating, by the power transmitter, a different time slot to each of the at least two inductive wireless power receivers for sending messages to the power transmitter,
• allocating, by the power transmitter, a synchronised power measurement time slot and sending a message to the power receivers announcing the synchronised power measurement time slot,
• measuring, by the power transmitter, during the power measurement time slot, the inductive wireless power transmitted by the power transmitter,
• receiving, by the power transmitter, from each of the power receivers, in each allocated time slot after the power measurement time slot, a message indicating the measured power received by that power receiver,
• calculating, by the power transmitter, the power loss from the measured inductive wireless power transmitted by the power transmitter and the measured inductive wireless powers received by each of the power receivers,
• reducing, by the power transmitter, the power of the inductive wireless power signal if the calculated power loss exceeds a threshold value.