Wireless power transfer control based on required and received power error

1. A transmitter for wireless power transfer comprising:

a power transmitting coil; and

control circuitry coupled to the power transmitting coil configured to:

receive a plurality of messages from a wireless power receiver, the plurality of messages allowing closed loop control of transmitter operation by the receiver;

monitor error indicators from the plurality of messages, the error indicators representing a magnitude of a difference between a power need of the receiver and power provided by the transmitter;

exert closed loop control of a wireless power transfer output level transmitted to the wireless power receiver based on at least some of the error indicators from the plurality of messages;

determine whether the error indicators exceed a non-zero power error threshold for a threshold time, wherein the threshold time is less than a control error packet timeout of the transmitter, the control error packet timeout being selected to prevent shutdown of the transmitter because of lost communication with the receiver; and

in accordance with determining that the error indicators exceed the non-zero power error threshold for the threshold time, perform a corrective action.

2. The transmitter of claim 1 wherein the error indicators are indicative of a difference between a required current at the receiver and a received current at the receiver.

3. The transmitter of claim 1 wherein the error indicators are indicative of a difference between a required voltage at the receiver and a received voltage at the receiver.

4. The transmitter of claim 1 wherein the plurality of messages are control error packets.

5. The transmitter of claim 1 wherein the control error packet timeout is 1.8 seconds.

6. The transmitter of claim 5 wherein the threshold time is between 50 milliseconds and 1000 milliseconds.

7. The transmitter of claim 6 wherein the threshold time is less than 500 milliseconds.

8. The transmitter of claim 6 wherein the threshold time is 250 milliseconds.

9. The transmitter of claim 1 wherein the threshold time is greater than a time constant of a load of the wireless power receiver.

10. The transmitter of claim 1 wherein the corrective action comprises a corrective action selected from the group consisting of: discontinuing transmission of wireless power using the power transmitting coil to the wireless power receiver, placing the transmitter in a standby mode, and placing the transmitter in a low power mode.

11. The transmitter of claim 1 wherein the transmitter is configured to transmit power up to a first maximum and the wireless power receiver is configured to receive power up to a second maximum that is less than the first maximum.

12. The transmitter of claim 1 wherein the threshold time is greater than a time constant of the wireless power receiver.

13. The transmitter of claim 1 wherein the threshold time is greater than an RC time constant of a load circuit in the wireless power receiver.

14. A transmitter for wirelessly transmitting power comprising:

a power transmitting coil; and

control circuitry coupled to the power transmitting coil configured to:

receive a plurality of messages from a wireless power receiver, the plurality of messages allowing closed loop control of transmitter operation by the receiver;

monitor error indicators from the plurality of messages, the error indicators representing a magnitude of a difference between a power need of the receiver and power provided by the transmitter;

exert closed loop control of a wireless power transfer output level transmitted to the wireless power receiver based on at least some of the error indicators from the plurality of messages;

in response to at least some of the error indicators from the plurality of messages indicating an equilibrium state in which the error indicators do not exceed a non-zero power error threshold, set an output threshold; and

in accordance with determining that an output from the transmitter exceeds the output threshold, perform a corrective action.

15. The transmitter of claim 14 wherein the equilibrium state is indicated when a magnitude of at least some of the error indicators from the plurality of messages is 0.

16. The transmitter of claim 14 , wherein the equilibrium state is indicated when an average of a group of at least some of the error indicators from the plurality of messages is within a tolerance range from −2 to +2.

17. The transmitter of claim 14 wherein the corrective action comprises discontinuing transmission of wireless power using the power transmitting coil to the wireless power receiver.

18. The transmitter of claim 14 wherein the transmitter is configured to transmit power up to a first maximum and the wireless power receiver is configured to receive power up to a second maximum that is less than the first maximum.

19. A transmitter for wirelessly transmitting power comprising:

a power transmitting coil; and

control circuitry coupled to the power transmitting coil configured to:

receive a plurality of messages from a wireless power receiver, the plurality of messages allowing closed loop control of transmitter operation by the receiver;

monitor error indicators from the plurality of messages, the error indicators representing a magnitude of a difference between a power need of the receiver and power provided by the transmitter;

exert closed loop control of a wireless power transfer output level transmitted to the wireless power receiver based on at least some of the error indicators from the plurality of messages;

in response to at least some of the error indicators from the plurality of messages indicating an equilibrium state in which the error indicators do not exceed a non-zero power error threshold, set an output slope threshold; and

in accordance with determining that a rate of change of a transmitter output exceeds the output slope threshold, perform a corrective action.

20. A receiver for wireless power transfer comprising:

a power receiving coil; and

control circuitry coupled to the power receiving coil configured to:

send a plurality of messages to a wireless power transmitter, the plurality of messages allowing closed loop control of transmitter operation by the receiver, each message including an error indicator, the error indicator representing a magnitude of a difference between a power need of the receiver and power provided by the transmitter;

receive a wireless power transfer input level transmitted from the wireless power transmitter based on the error indicators;

monitor the error indicators from the plurality of messages;

determine whether the error indicators exceed a non-zero power error threshold for a threshold time, wherein the threshold time is less than a control error packet timeout of the transmitter, the control error packet timeout being selected to prevent shutdown of the transmitter because of lost communication with the receiver; and

in accordance with determining that the error indicators exceed the non-zero power error threshold for the threshold time, perform a corrective action.

21. The receiver of claim 20 , wherein the error indicators are indicative of a difference between a required current at the receiver and a received current at the receiver.

22. The receiver of claim 20 , wherein the error indicators are indicative of a difference between a required voltage at the receiver and a received voltage at the receiver.

23. The receiver of claim 20 , wherein the plurality of messages are control error packets.

24. The receiver of claim 20 , wherein the threshold time is less than 1.8 seconds.

25. The receiver of claim 20 , wherein the corrective action comprises isolating a load of the receiver.