Systems and methods for identifying an ideal operation frequency for wireless power transfer

1. A method for wirelessly transmitting power to power or charge a wireless power receiver, the method comprising:

during a first time period, transmitting power at a first power level from a wireless power transmitter to the wireless power receiver;

determining a frequency for transmitting power at a second power level based on a ratio of a current level of the wireless power receiver to a current level of a wireless power transmitter at the first power level;

during a second time period, transmitting power at the second power level and at the frequency, the first power level lower than the second power level.

2. The method of claim 1 , wherein determining the frequency comprises:

identifying the ratio of the current level of the wireless power transmitter to the current level of the wireless power receiver;

at a first frequency:

operating the wireless power transmitter at a first current level,

transferring power to the wireless power receiver such that the current level of the wireless power receiver satisfies the ratio, and

obtaining a measurement of a first output current level at the wireless power receiver;

at a second frequency:

operating the wireless power transmitter at the first current level,

transferring power to the wireless power receiver such that the current level of the wireless power receiver satisfies the ratio,

obtaining a measurement of a second output current level at the wireless power receiver;

comparing the first output current level with the second output current level; and

selecting the first or second frequency based on the comparison.

3. The method of claim 1 , wherein determining the frequency comprises:

identifying the ratio of the current level of the wireless power transmitter to the current level of the wireless power receiver;

at a first frequency:

operating the wireless power transmitter at a first current level,

transferring power to the wireless power receiver such that an output current level of the wireless power receiver remains substantially constant,

adjusting the first current level of the wireless power transmitter such that the current level of the wireless power receiver satisfies the ratio,

measuring the first current level of the wireless power transmitter at the ratio;

at a second frequency:

operating the wireless power transmitter at a second current level,

transferring power to the wireless power receiver such that an output current level of the wireless power receiver remains substantially constant,

adjusting the second current level of the wireless power transmitter such that the current level of the wireless power receiver satisfies the ratio,

measuring the second current level of the wireless power transmitter at the ratio;

comparing the first current level with the second current level; and

selecting the first or second frequency based on the comparison.

4. The method of claim 1 , wherein a ratio of a first current level of the wireless power receiver to a first current level of the wireless power transmitter at the first power level is the same as a ratio of a second current level of the wireless power receiver to a second current level of the wireless power transmitter at the second power level.

5. The method of claim 1 , wherein the ratio is based on predefined maximum current levels of the wireless power transmitter and the wireless power receiver.

6. The method of claim 1 , wherein the ratio is based on maximum current levels of the wireless power transmitter and the wireless power receiver communicated between the wireless power transmitter and the wireless power receiver.

7. The method of claim 1 , wherein the first power level is a fraction of the second power level.

8. The method of claim 1 , wherein determining the frequency comprises:

determining a number of frequency adjustments during the first time period;

for each of the number of frequency adjustments:

transferring power to the wireless power receiver based on the ratio, and

obtaining a measurement of a output current level at the wireless power receiver; and

selecting the frequency with the highest measurement of the output current level at the wireless power receiver.

9. The method of claim 1 , wherein determining the frequency comprises:

determining a number of frequency adjustments during the first time period;

for each of the number of frequency adjustments:

transferring power to the wireless power receiver based on the ratio, and

obtaining a measurement of a current level of the wireless power transmitter; and

selecting the frequency with the lowest measurement of the current level of the wireless power transmitter.

10. An apparatus for wirelessly transmitting power to power or charge a wireless power receiver, comprising:

a transmit circuit configured to, during a first time period, transmit power at a first power level to the wireless power receiver; and

a processor circuit configured to determine a frequency for transmitting power at a second power level based on a ratio of a current level of the wireless power receiver to a current level of the transmit circuit at the first power level, wherein the transmit circuit is further configured to, during a second time period, transmit power at a second power level and at the frequency, the first power level lower than the second power level.

11. The apparatus of claim 10 , wherein the processor circuit is further configured to:

identify the ratio of the current level of the wireless power transmitter to the current level of the wireless power receiver;

at a first frequency:

operate the transmit circuit at a first current level to transfer power to the wireless power receiver such that the current level of the wireless power receiver satisfies the ratio, and

obtain a measurement of a first output current level at the wireless power receiver;

at a second frequency:

operate the transmit circuit at the first current level to transfer power to the wireless power receiver such that the current level of the wireless power receiver satisfies the ratio,

obtain a measurement of a second output current level at the wireless power receiver;

compare the first output current level with the second output current level; and

select the first or second frequency based on the comparison.

12. The apparatus of claim 10 , wherein the processor circuit is further configured to:

identify the ratio of the current level of the transmit circuit to the current level of the wireless power receiver;

at a first frequency:

operate the transmit circuit at a first current level to transfer power to the wireless power receiver such that an output current level of the wireless power receiver remains substantially constant,

adjust the first current level of the wireless power transmitter such that the current level of the wireless power receiver satisfies the ratio,

measure the first current level of the wireless power transmitter at the ratio;

at a second frequency:

operate the transmit circuit at a second current level to transfer power to the wireless power receiver such that an output current level of the wireless power receiver remains substantially constant,

adjust the second current level of the transmit circuit such that the current level of the wireless power receiver satisfies the ratio,

measure the second current level of the transmit circuit at the ratio;

compare the first current level with the second current level; and

select the first or second frequency based on the comparison.

13. The apparatus of claim 10 , wherein a ratio of a first current level of the wireless power receiver to a first current level of the transmit circuit at the first power level is the same as a ratio of a second current level of the wireless power receiver to a second current level of the transmit circuit at the second power level.

14. The apparatus of claim 10 , wherein the ratio is based on predefined maximum current levels of the transmit circuit and the wireless power receiver.

15. The apparatus of claim 10 , wherein the ratio is based on maximum current levels of the transmit circuit and the wireless power receiver communicated between the apparatus and the wireless power receiver.

16. The apparatus of claim 10 , wherein the first power level is a fraction of the second power level.

17. The apparatus of claim 10 , wherein the processor circuit is further configured to:

determine a number of frequency adjustments during the first time period;

for each of the number of frequency adjustments:

operate the transmit circuit to transfer power to the wireless power receiver based on the ratio, and

obtain a measurement of a output current level at the wireless power receiver; and

select the frequency with a highest measurement of the output current level at the wireless power receiver.

18. The apparatus of claim 10 , wherein the processor circuit is further configured to:

determine a number of frequency adjustments during the first time period;

for each of the number of frequency adjustments:

operate the transmit circuit to transfer power to the wireless power receiver based on the ratio, and

obtain a measurement of a current level of the transmit circuit; and

select the frequency with a lowest measurement of the current level of the transmit circuit.

19. An apparatus for wirelessly transmitting power to power or charge a wireless power receiver, comprising:

means for transmitting power at a first power level, during a first time period, to the wireless power receiver;

means for determining a frequency for transmitting power at a second power level based on a ratio of a current level of the wireless power receiver to a current level of the transmitting means at the first power level;

means for transmitting power at the second power level and at the frequency, during a second time period, the first power level lower than the second power level.

20. The apparatus of claim 19 , further comprising:

means for identifying the ratio of the current level of the transmitting means to the current level of the wireless power receiver;

at a first frequency:

means for operating the transmitting means at a first current level,

means for transferring power to the wireless power receiver such that the current level of the wireless power receiver satisfies the ratio, and

means for obtaining a measurement of a first output current level at the wireless power receiver;

at a second frequency:

means for operating the transmitting means at the first current level,

means for transferring power to the wireless power receiver such that the current level of the wireless power receiver satisfies the ratio,

means for obtaining a measurement of a second output current level at the wireless power receiver;

means for comparing the first output current level with the second output current level; and

means for selecting the first or second frequency based on the comparison.

21. The apparatus of claim 19 , further comprising:

means for identifying the ratio of the current level of the transmitting means to the current level of the wireless power receiver;

at a first frequency:

means for operating the transmitting means at a first current level,

means for transferring power to the wireless power receiver such that an output current level of the wireless power receiver remains substantially constant,

means for adjusting the first current level of the transmitting means such that the current level of the wireless power receiver satisfies the ratio,

means for measuring the first current level of the transmitting means at the ratio;

at a second frequency:

means for operating the transmitting means at a second current level,

means for transferring power to the wireless power receiver such that an output current f the wireless power receiver remains substantially constant,

means for adjusting the second current level of the transmitting means such that the current, level of the wireless power receiver satisfies the ratio,

means for measuring the second current level of the transmitting means at the ratio;

means for comparing the first current level with the second current level; and

means for selecting the first or second frequency based on the comparison.

22. The apparatus of claim 19 , wherein a ratio of a first current level of the wireless power receiver to a first current level of the transmitting means at the first power level is the same as a ratio of a second current level of the wireless power receiver to a second current level of the transmitting means at the second power level.

23. The apparatus of claim 19 , wherein the ratio is based on predefined maximum current levels of the transmitting means and the wireless power receiver.

24. The method of claim 1 , wherein the ratio is based on maximum current levels of the transmitting means and the wireless power receiver communicated between the transmitting means and the wireless power receiver.

25. The apparatus of claim 19 , wherein the first power level is a fraction of the second power level.

26. A non-transitory computer readable storage medium comprising instructions that when executed cause an apparatus to perform a method for wirelessly transmitting power to a wireless power receiver, comprising:

during a first time period, transmitting power at a first power level from a wireless power transmitter to the wireless power receiver;

determining a frequency for transmitting power at a second power level based on a ratio of a current level of the wireless power receiver to a current level of a wireless power transmitter at the first power level;

during a second time period, transmitting power at the second power level and at the frequency, the first power level lower than the second power level.

27. The medium of claim 26 , wherein determining the frequency comprises:

identifying the ratio of the current level of the wireless power transmitter to the current level of the wireless power receiver;

at a first frequency:

operating the wireless power transmitter at a first current level,

transferring power to the wireless power receiver such that the current level of the wireless power receiver satisfies the ratio, and

obtaining a measurement of a first output current level at the wireless power receiver;

at a second frequency:

operating the wireless power transmitter at the first current level,

transferring power to the wireless power receiver such that the current level of the wireless power receiver satisfies the ratio,

obtaining a measurement of a second output current level at the wireless power receiver;

comparing the first output current level with the second output current level; and

selecting the first or second frequency based on the comparison.

28. The medium of claim 26 , wherein determining the frequency comprises:

identifying the ratio of the current level of the wireless power transmitter to the current level of the wireless power receiver;

at a first frequency:

operating the wireless power transmitter at a first current level,

transferring power to the wireless power receiver such that an output current level of the wireless power receiver remains substantially constant,

adjusting the first current level of the wireless power transmitter such that the current level of the wireless power receiver satisfies the ratio,

measuring the first current level of the wireless power transmitter at the ratio;

at a second frequency:

operating the wireless power transmitter at a second current level,

transferring power to the wireless power receiver such that an output current level of the wireless power receiver remains substantially constant,

adjusting the second current level of the wireless power transmitter such that the current level of the wireless power receiver satisfies the ratio,

measuring the second current level of the wireless power transmitter at the ratio;

comparing the first current level with the second current level; and

selecting the first or second frequency based on the comparison.

29. The medium of claim 26 , wherein a ratio of a first current level of the wireless power receiver to a first current level of the wireless power transmitter at the first power level is the same as a ratio of a second current level of the wireless power receiver to a second current level of the wireless power transmitter at the second power level.

30. The medium of claim 26 , wherein the ratio is based on predefined maximum current levels of the wireless power transmitter and the wireless power receiver.