Active rectification in wireless power systems

1. An active rectifier for a wireless power receiver, the active rectifier comprising:

a first diode coupled between a first input of the active rectifier and an output of the active rectifier;

a first transistor coupled between the first input and ground;

a first capacitive snubber coupled in parallel to at least one of: (i) the first diode or (ii) the first transistor;

a second diode coupled between a second input of the active rectifier and the output of the active rectifier;

a second transistor coupled between the second input and ground; and

a second capacitive snubber coupled in parallel to at least one of: (i) the second diode or (ii) the second transistor,

wherein the first and second capacitive snubbers are configured to compensate for a shift in a reactive impedance of the active rectifier, and wherein the shift is based on an input current to the active rectifier.

2. The active rectifier of claim 1 wherein the first and second capacitive snubbers are configured to reduce a reactive current in the wireless power receiver.

3. The active rectifier of claim 1 wherein the first and second capacitive snubbers are configured to reduce a switching loss of the respective first and second transistors.

4. The active rectifier of claim 1 wherein each of the first capacitive snubber and the second capacitive snubber comprises a resistive component.

5. The active rectifier of claim 1 wherein each of the first capacitive snubber and the second capacitive snubber comprises a plurality of capacitors.

6. The active rectifier of claim 1 wherein the wireless power receiver is configured to deliver power of approximately 11 kW to a load coupled to the output of the active rectifier, and

wherein each capacitive snubber has a capacitance value between 1-30 nanoFarads.

7. The active rectifier of claim 1 wherein the active rectifier is configured to operate at a frequency of 85 kHz+/−10 kHz.

8. The active rectifier of claim 1 wherein the wireless power receiver comprises a receiver resonator coil configured to couple via an electromagnetic field to a wireless power transmitter, and

wherein, when the active rectifier is operating, an impedance presented by the active rectifier to the receiver resonator coil is resistive.

9. The active rectifier of claim 1 wherein the active rectifier is configured to provide current for charging a battery coupled to the output of the active rectifier.

10. The active rectifier of claim 1 wherein the active rectifier is configured to provide current to a resistor coupled to the output of the active rectifier.

11. The active rectifier of claim 1 wherein the shift in the reactive impedance of the active rectifier is based on frequency content of the input current.

12. The active rectifier of claim 1 wherein the input current is received at the first and second inputs of the active rectifier.

13. A wireless power receiver comprising:

a receiver resonator coil configured to couple via an electromagnetic field to a wireless power transmitter; and

an active rectifier coupled to an output of the receiver resonator coil, the active rectifier comprising:

a first diode coupled between a first input of the active rectifier and an output of the active rectifier;

a first transistor coupled between the first input and ground;

a first capacitive snubber coupled in parallel to at least one of: (i) the first diode or (ii) the first transistor;

a second diode coupled between a second input of the active rectifier and the output of the active rectifier;

a second transistor coupled between the second input and ground; and

a second capacitive snubber coupled in parallel to at least one of: (i) the second diode or (ii) the second transistor,

wherein the first and second capacitive snubbers are configured to compensate for a shift in a reactive impedance of the active rectifier, and wherein the shift is based on an input current to the active rectifier.

14. The wireless power receiver of claim 13 wherein the first and second capacitive snubbers are configured to reduce a reactive current in the wireless power receiver.

15. The wireless power receiver of claim 13 wherein the first and second capacitive snubbers are configured to reduce a switching loss of the respective first and second transistors.

16. The wireless power receiver of claim 13 wherein each of the first capacitive snubber and the second capacitive snubber comprises a resistive component.

17. The wireless power receiver of claim 13 wherein each of the first capacitive snubber and the second capacitive snubber comprises a plurality of capacitors.

18. The wireless power receiver of claim 13 wherein the wireless power receiver is configured to deliver power of approximately 11 kW to a load coupled to the output of the active rectifier, and

wherein each capacitive snubber has a capacitance value between 1-30 nanoFarads.

19. The wireless power receiver of claim 13 wherein the active rectifier is configured to operate at a frequency of 85 kHz+/−10 kHz.

20. The wireless power receiver of claim 13 wherein, when the active rectifier is operating, an impedance presented by the active rectifier to the receiver resonator coil is resistive.

21. The wireless power receiver of claim 13 wherein the active rectifier is configured to provide current for charging a battery coupled to the output of the active rectifier.

22. The wireless power receiver of claim 13 wherein the active rectifier is configured to provide current to a resistor coupled to the output of the active rectifier.

23. The wireless power receiver of claim 13 wherein the shift in the reactive impedance of the active rectifier is based on frequency content of the input current.

24. The wireless power receiver of claim 13 wherein the input current is received at the first and second inputs of the active rectifier.