received by the International Bureau on 15 March 2019 (15.03.2019)

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, monitor error indicators from the plurality of messages, control 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 if the error indicators exceed a power error threshold for a threshold time, and

perform a corrective action if the error indicators exceed the power error threshold for the threshold time.

2. The transmitter according to claim 1 wherein the error indicators are indicative of a difference between a required current or voltage at the receiver, and a received current or voltage at the receiver. 3. The transmitter according to claim 1 wherein the plurality of messages are control error packets.

4. The transmitter according to claim 1 wherein the threshold time is less than

approximately 1.8 seconds.

5. The transmitter according to claim 4 wherein the threshold time is in a range of between 50 to 1000 milliseconds.

6. The transmitter according to claim 5 wherein the threshold time is less than 500 milliseconds or the threshold time is approximately 250 milliseconds.

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

8. The transmitter according to claim 1 wherein the corrective action is one or more of: discontinuing transmission of wireless power using the power transmitting coil to the wireless power receiver, placing the transmitter in a standby mode or placing the transmitter in a low power mode.

9. The transmitter according to claim 1 wherein the transmitter is configured to transmit power up to a first maximum and the receiver is configured to receive power up to a second maximum, less than the first maximum.

10. 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, monitor error indicators from the plurality of messages, control 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,

set an output threshold when at least some of the error indicators from the plurality of messages indicate an equilibrium state, and

perform a corrective action if an output from the transmitter exceeds the output threshold.

11. The transmitter according to claim 10 wherein the equilibrium state is indicated when a magnitude of at least some of the error indicators from the plurality of messages is 0, or when an average of a group of at least some of the error indicators from the plurality of messages is 0 or within a tolerance range from -2 to +2.

12. The transmitter according to claim 10 wherein the corrective action is

discontinuing transmission of wireless power using the power transmitting coil to the wireless power receiver.

13. The transmitter according to claim 10 wherein the transmitter is configured to transmit power up to a first maximum and the receiver is configured to receive power up to a second maximum, less than the first maximum.

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, monitor error indicators from the plurality of messages,

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control 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,

set an output slope threshold when at least some of the error indicators from the plurality of messages indicate an equilibrium state, and perform a corrective action if a rate of change of a transmitter output exceeds the output slope threshold.

15. A method for wireless power transfer comprising :

receiving a plurality of messages from a wireless power receiver,

monitoring error indicators from the plurality of messages,

controlling a wireless power transfer output level transmitted from a wireless power transmitter to the wireless power receiver based on at least some of the error indicators from the plurality of messages,

determine if the error indicators exceed a power error threshold for a threshold time, and

perform a corrective action if the error indicators exceed a power error threshold for a threshold time.