Controlling wireless power transfer systems

1. A wireless energy transfer system comprising:

an energy transmitter comprising a transmitter-impedance matching network (IMN), the transmitter configured to perform operations comprising:

performing a first comparison between a characteristic of a power of the transmitter and a target power; and

adjusting, based on the first comparison, a reactance of the transmitter-IMN to adjust the power of the transmitter; and

an energy receiver comprising a receiver-IMN, the receiver configured to perform operations comprising; determining an efficiency of the wireless energy transfer system at a second time based on power data from the transmitter;

performing a second comparison between the efficiency at the second time and an efficiency of the wireless energy transfer system at a first time, the first time being prior to the second time; and

adjusting, based on the second comparison, a reactance of the receiver-IMN.

2. The system of claim 1 , wherein adjusting the reactance of the receiver-IMN comprises adjusting the reactance of the receiver-IMN by a variable reactance adjustment value.

3. The system of claim 1 , wherein the first comparison and adjustment to the reactance of the transmitter-IMN occur iteratively until the characteristic of the power is within a threshold value of the target power.

4. The system of claim 1 , wherein adjusting the reactance of the receiver-IMN comprises in response to the efficiency at the second time being less than the efficiency at the first time, negating a reactance adjustment value, and wherein adjusting the reactance of the receiver-IMN comprises adjusting the reactance of the receiver-IMN by the negated reactance adjustment value.

5. The system of claim 1 , wherein adjusting the reactance of the transmitter-IMN comprises in response to the power being less than the target power, adjusting the reactance of the transmitter-IMN by a first reactance adjustment value and in response to the power being greater than the target power, adjusting the reactance of the transmitter-IMN by a second, different reactance adjustment value.

6. The system of claim 1 , wherein the transmitter is an electric vehicle charger and wherein the receiver is a coupled to a power system of an electric vehicle.

7. The system of claim 1 , wherein the first comparison is between a power factor of the power of the transmitter and a target power factor, and wherein the operations of the transmitter further comprise:

a third comparison between a magnitude of the power and a target power magnitude, wherein the third comparison follows the first comparison; and

adjusting, based on the third comparison, a bus voltage of the transmitter to adjust the power of the transmitter.

8. The system of claim 7 , wherein the power factor is represented by a phase relationship between a transmitter voltage and a transmitter current.

9. The system of claim 7 , wherein the first comparison and adjustment of the reactance of the transmitter-IMN based on the first comparison occur iteratively until the power factor of the power is within a threshold value of the target power factor.

10. The system of claim 7 , wherein the steps of performing the first comparison and adjusting the reactance of the transmitter-IMN are iterated at a faster rate than the steps of performing the third comparison and adjusting the bus voltage.

11. The system of claim 1 , wherein the operations of the transmitter further comprise shutting down the wireless energy transfer system by reducing the target power to zero.

12. The system of claim 1 , wherein the operations of the transmitter further comprise starting up the transmitter by adjusting the reactance of the transmitter-IMN to a maximum value.

13. The system of claim 1 , wherein the operations of the transmitter further comprise starting up the transmitter by adjusting a frequency of an inverter to a target frequency.

14. The system of claim 1 , wherein the operations of the receiver further comprise starting up the receiver by adjusting the reactance of the receiver-IMN to a minimum value.

15. The system of claim 1 , wherein the transmitter-IMN comprises a tunable reactive element electrically connected between an inverter and at least one fixed reactive element, and wherein adjusting the reactance of the transmitter-IMN comprises adjusting the tunable reactive element.

16. The system of claim 1 , wherein the receiver-IMN comprises a tunable reactive element electrically connected between a rectifier and at least one fixed reactive element, and wherein adjusting the reactance of the receiver-IMN comprises adjusting the tunable reactive element.

17. The system of claim 1 , wherein the steps of performing the first comparison and adjusting the reactance of the transmitter-IMN are iterated at a faster rate than the steps of performing the second comparison and adjusting the reactance of the receiver-IMN.

18. The system of claim 1 , wherein determining the efficiency of the wireless energy transfer system comprises:

receiving power data from the transmitter;

determining an output power of the receiver; and

calculating the efficiency of the wireless energy transfer system based on the power data from the transmitter and the output power of the receiver.