Methods and apparatus for tuning and controlling double couple inductive power transfer systems

1. An apparatus for transmitting charging power wirelessly to a vehicle, the apparatus comprising:

a first coupler having a first reactance at an operating frequency and configured to wirelessly receive power from a backbone power source, the first coupler wound on a ferromagnetic core;

a first capacitor having a second reactance at the operating frequency and electrically connected in series with the first coupler, the second reactance having a magnitude equal to a magnitude of the first reactance;

a second capacitor electrically connected in parallel across the first coupler and the first capacitor;

a first base coupler configured to wirelessly transfer power to a vehicle pad, the first base coupler configured to be electrically connected in parallel across the second capacitor via a first switch;

a second coupler wound on the same ferromagnetic core and inductively coupled to the backbone power source, wherein the first and second couplers are coupled via magnetic flux passing through the ferromagnetic core; and

a shunt switch electrically connected to the second coupler and configured to short circuit the second coupler when the shunt switch is closed; and

a plurality of base couplers including the first base coupler and a plurality of switches including the first switch, each of the plurality of base couplers configured to be electrically connected in parallel across the second capacitor via a corresponding switch of the plurality of switches, wherein a switch controller is configured to close the corresponding one of the plurality of switches and open the shunt switch to energize a selected one of the plurality of base couplers.

2. The apparatus of claim 1 , a magnitude of a peak voltage across the second capacitor being proportional to a magnitude of a peak voltage induced in the first coupler at the operating frequency.

3. The apparatus of claim 1 , the first reactance comprising a leakage inductance and the second reactance comprising a capacitance, the capacitance configured to substantially cancel out the leakage inductance at the operating frequency.

4. The apparatus of claim 1 , the second capacitor having a third reactance at the operating frequency and base couplers of the plurality of base couplers that are electrically connected in parallel across the second capacitor having a combined reactance, the third reactance having a magnitude equal to a magnitude of the combined reactance.

5. The apparatus of claim 1 , further comprising a power flow controller comprising the second coupler and the shunt switch, wherein the power flow controller comprises a boost converter.

6. The apparatus of claim 1 , further comprising the switch controller that is configured to

close the shunt switch and open the corresponding one of the plurality of switches to de-energize the selected one of the base couplers.

7. The apparatus of claim 1 , further comprising a shunt capacitor connected in parallel with the shunt switch.

8. The apparatus of claim 7 , wherein the shunt capacitor is configured to provide a voltage to a power supply rail.

9. A method for transmitting charging power wirelessly to a vehicle, the method comprising:

selecting a first reactance of a first coupler to have a magnitude equal to a magnitude of a second reactance of a first capacitor at an operating frequency, the first coupler wound on a ferromagnetic core and electrically connected in series with the first capacitor;

receiving power wirelessly from a backbone power source utilizing the first coupler;

selectively electrically connecting a first base coupler configured to wirelessly transfer power to a vehicle pad in parallel across a second capacitor electrically connected in parallel across the first coupler and the first capacitor utilizing a first switch;

providing the power to the first base coupler;

receiving power wirelessly from the backbone power source inductively coupled to a second coupler wound on the same ferromagnetic core, wherein the first and second couplers are coupled via magnetic flux passing through the ferromagnetic core;

short circuiting the second coupler by closing a shunt switch connected to the second coupler;

selectively electrically connecting at least one of a plurality of base couplers including the first base coupler in parallel across the second capacitor utilizing a corresponding at least one of a plurality of switches including the first switch; and

energizing a selected one of the plurality of base couplers by closing the corresponding one of the plurality of switches and then opening the shunt switch.

10. The method of claim 9 , comprising providing a first voltage across the second capacitor, the first voltage having a peak magnitude proportional to a peak magnitude of a voltage induced in the first coupler at the operating frequency.

11. The method of claim 9 , a capacitance of the second reactance substantially cancelling out a leakage inductance of the first reactance at the operating frequency.

12. The method of claim 9 , comprising selecting a third reactance of the second capacitor to have a magnitude equal to a magnitude of a combined reactance of the connected at least one of the plurality of base couplers.

13. The method of claim 9 , further comprising

de-energizing the selected one of the base couplers by closing the shunt switch and then opening the corresponding one of the plurality of switches.

14. The method of claim 9 , comprising storing power diverted to a shunt capacitor connected in parallel with the shunt switch.

15. The method of claim 14 , comprising providing a voltage to a power supply rail utilizing the shunt capacitor.

16. A non-transitory computer-readable medium comprising code that, when executed, causes an apparatus to:

select a first reactance of a first coupler to have a magnitude equal to a magnitude of a second reactance of a first capacitor at the operating frequency, the first coupler wound on a ferromagnetic core and electrically connected in series with the first capacitor;

receive power wirelessly from a backbone power source utilizing the first coupler;

selectively electrically connect a first base coupler configured to wireless transfer power to a vehicle pad in parallel across a second capacitor electrically connected in parallel across the first coupler and the first capacitor utilizing a first switch;

provide the power to the first base coupler;

receive power wirelessly from the backbone power source inductively coupled to a second coupler wound on the same ferromagnetic core, wherein the first and second couplers are coupled via magnetic flux passing through the ferromagnetic core; and

short circuit the second coupler by closing a shunt switch connected to the second coupler;

selectively electrically connect at least one of a plurality of base couplers including the first base coupler in parallel across the second capacitor utilizing a corresponding at least one of a plurality of switches including the first switch; and

close the corresponding one of the plurality of switches and open the shunt switch to energize a selected one of the plurality of base couplers.

17. The non-transitory computer-readable medium of claim 16 , wherein the code, when executed, causes the apparatus to provide a first voltage across the second capacitor, the first voltage having a peak magnitude proportional to a peak magnitude of a voltage induced in the first coupler at the operating frequency.

18. The non-transitory computer-readable medium of claim 16 , wherein a capacitance of the second reactance substantially cancels out a leakage inductance of the first reactance at the operating frequency.

19. The non-transitory computer-readable medium of claim 16 , wherein the code, when executed, causes the apparatus to select a third reactance of the second capacitor to have a magnitude equal to a magnitude of a combined reactance of the connected at least one of the plurality of base couplers.

20. The non-transitory computer-readable medium of claim 16 , wherein the code, when executed, further causes the apparatus to

close the shunt switch and open the corresponding one of the plurality of switches to de-energize the selected one of the base couplers.

21. The non-transitory computer-readable medium of claim 16 , wherein the code, when executed, causes the apparatus to store power diverted to a shunt capacitor connected in parallel with the shunt switch.

22. An apparatus for transmitting charging power wirelessly to a vehicle, the apparatus comprising:

means for directing magnetic flux;

first means for wirelessly receiving power from a backbone power source, the first means for wirelessly receiving power having a first reactance at an operating frequency and wound on the means for directing magnetic flux;

first means for storing electric charge having a second reactance at the operating frequency and electrically connected with the means for wirelessly receiving power, the second reactance having a magnitude equal to a magnitude of the first reactance;

second means for storing electric charge electrically connected with the means for wirelessly receiving power and the first means for storing electric charge;

first means for wirelessly transmitting power to a vehicle pad electrically connected with the second means for storing electric charge via a first switch;

second means for wirelessly receiving power from the backbone power source inductively coupled to the power source, the second means for wirelessly receiving power wound on the same means for directing magnetic flux, wherein the first and second means for wirelessly receiving power are coupled via the magnetic flux passing through the means for directing magnetic flux;

means for short circuiting the second means for wirelessly receiving power, the means for short circuiting connected to the second means for wirelessly receiving power; and

means for selectively electrically connecting at least one of a plurality of means for wirelessly transmitting power, including the first means for wirelessly transmitting power, in parallel across the second capacitor utilizing a corresponding at least one of a plurality of switches including the first switch; and

energizing a selected one of the plurality of means for wirelessly transmitting by closing the corresponding one of the plurality of switches and then opening the means for short circuiting the second means for wirelessly receiving power.

23. The apparatus of claim 22 , comprising a plurality of means for wirelessly transmitting power including the first means for wirelessly transmitting power, each of the plurality of means for wirelessly transmitting power configured to be electrically connected to the second means for storing charge.