Power flow controller synchronization

1. An apparatus for receiving power in a wireless power transfer system, comprising:

a power receiving element;

a tuning and current doubler circuit operably coupled to the power receiving element, wherein the tuning and current doubler circuit includes a first diode, a second diode, and a single inductor, wherein the single inductor is only one inductor of the tuning and current doubler circuit, wherein:

a cathode end of the first diode is electrically coupled to the single inductor, a first terminal of a capacitor, and the power receiving element; an anode end of the first diode is electrically coupled to an anode end of the second diode and to a ground; and

a cathode end of the second diode is electrically coupled to a second terminal of the capacitor and the power receiving element;

a power flow controller circuit including a transistor device operably coupled to the tuning and current doubler circuit; and

a controller operably coupled to the power receiving element and the power flow controller circuit and configured to detect a signal in the power receiving element and to synchronize the power flow controller circuit based on the signal.

2. The apparatus of claim 1 wherein the controller is configured to synchronize the power flow controller circuit based on a negative zero crossover point in the signal.

3. The apparatus of claim 1 wherein the controller is configured to synchronize the power flow controller circuit based on a positive zero crossover point in the signal.

4. The apparatus of claim 1 further comprising a power output operably coupled to the power flow controller circuit.

5. The apparatus of claim 4 wherein the power output includes a battery.

6. The apparatus of claim 1 wherein the signal in the power receiving element is a voltage signal in the power receiving element.

7. The apparatus of claim 6 wherein a frequency of the voltage signal is in a range of 80 to 90 kHz.

8. The apparatus of claim 1 wherein the controller is configured to determine a duty cycle of the power flow controller circuit.

9. The apparatus of claim 8 wherein the duty cycle is based on an inductor current value in the tuning and current doubler circuit.

10. The apparatus of claim 1 wherein the signal is a current signal in the power receiving element.

11. The apparatus of claim 1 wherein the power receiving element receives power via an inductive coupling with a transmitter.

12. A method of controlling a receiver in a wireless power transfer system, comprising:

detecting a signal in a power receiving element, wherein the signal is at an operating frequency; determining a synchronization point in the signal;

activating a transistor device in a power flow controller based on the synchronization point and the operating frequency; and

wherein a tuning and current doubler circuit is operably coupled to the power receiving element and includes a first diode, a second diode, and a single inductor, wherein the single inductor is only one inductor of the tuning and current doubler circuit, wherein:

a cathode end of the first diode is electrically coupled to the single inductor, a first terminal of a capacitor, and the power receiving element:

an anode end of the first diode is electrically coupled to an anode end of the second diode and to a ground; and

a cathode end of the second diode is electrically coupled to a second terminal of the capacitor and the power receiving element.

13. The method of claim 12 wherein the determining the synchronization point includes determining a negative zero voltage crossing point in the signal.

14. The method of claim 12 wherein the determining the synchronization point includes determining a positive zero voltage crossing point in the signal.

15. The method of claim 12 further comprising:

determining a power receiving element inductance value;

determining a power flow controller duty cycle based on the power receiving element inductance value; and

activating the transistor device in the power flow controller based at least in part on the power flow controller duty cycle.

16. The method of claim 12 wherein the activating the transistor device in the power flow controller includes controlling a drain to source voltage in the transistor device based on the synchronization point and the operating frequency.

17. The method of claim 12 wherein the signal is a voltage signal in the power receiving element.

18. The method of claim 12 further comprising:

determining an electrical current output to a battery, wherein the battery is operably coupled to the power flow controller via an output filter;

determining a power flow controller duty cycle based on the electrical current output; and

activating the transistor device in the power flow controller based at least in part on the power flow controller duty cycle.

19. The method of claim 18 wherein the power flow controller duty cycle is between 0% and 50%.

20. A non-transitory processor-readable storage medium comprising instructions for controlling a receiver in a wireless power transfer, comprising:

code for detecting a signal in a power receiving element, wherein the signal is at an operating frequency;

code for determining a synchronization point in the signal; and

code for activating a transistor device in a power flow controller based on the synchronization point and the operating frequency, wherein a tuning and current doubler circuit is operably coupled to the power receiving element and includes a first diode, a second diode, and a single inductor, wherein the single inductor is only one inductor of the tuning and current doubler circuit, wherein:

a cathode end of the first diode is electrically coupled to the single inductor, a first terminal of a capacitor, and the power receiving element:

an anode end of the first diode is electrically coupled to an anode end of the second diode and to a ground, and

a cathode end of the second diode is electrically coupled to a second terminal of the capacitor and the power receiving element.