Impedance adjustment in wireless power transmission systems and methods

1. A power transmitting apparatus configured to wirelessly transmit power to a power receiving apparatus connected to an electrical load, the power transmitting apparatus comprising:

a circuit comprising an inductive element formed by at least one loop of conductive material, wherein the inductive element forms a resonator with at least a portion of the circuit; and

a controller configured to:

receive information about a phase difference between a voltage waveform and a current waveform associated with impedance matching circuitry of a power source of the power transmitting apparatus;

determine whether the phase difference is within an allowable range of phase differences;

adjust an impedance of the circuit if the phase difference is outside the allowable range of phase differences; and

adjust at least one of a phase, a duty cycle, and a bus voltage of an amplifier of the power source if the phase difference is within the allowable range of phase differences to drive the power transmitting apparatus toward a target output power.

2. The apparatus of claim 1 , wherein the controller is further configured to receive information about a phase difference between a voltage waveform and a current waveform associated with an amplifier of the power source of the power transmitting apparatus.

3. The apparatus of claim 1 , wherein the voltage and current waveforms correspond to one member selected from the group consisting of voltage and current waveforms within the impedance matching circuitry, voltage and current waveforms at an output of the impedance matching circuitry, and voltage and current waveforms at an input of the impedance matching circuitry.

4. The apparatus of claim 1 , wherein the controller is configured to adjust the impedance of the circuit to reduce the phase difference.

5. The apparatus of claim 4 , further comprising:

a detector coupled to the power source and to the controller, and comprising:

a first input terminal configured to receive a first waveform corresponding to the voltage waveform;

a second input terminal configured to receive a second waveform corresponding to the current waveform; and

at least one logic unit, wherein the at least one logic unit is configured to generate an output waveform that corresponds to the phase difference between the first and second waveforms; and

wherein the controller is configured to receive the output waveform from the detector.

6. The apparatus of claim 5 , wherein the at least one logic unit comprises:

a first logic unit connected to the first and second input terminals and configured to produce a third waveform based on the first and second waveforms; and

a second logic unit configured to receive the third waveform and configured to produce the output waveform based on the third waveform.

7. The apparatus of claim 5 , wherein the output waveform comprises a pulse having a width that corresponds to a temporal offset between the first and second electrical signals.

8. The apparatus of claim 7 , wherein the first logic unit is configured to perform an AND logical operation, and the second logic unit is configured to perform an XOR logical operation.

9. The apparatus of claim 4 , wherein the controller is configured to reduce the impedance of the circuit to reduce the phase difference.

10. The apparatus of claim 4 , wherein the controller is configured to increase the impedance of the circuit to increase the phase difference.

11. The apparatus of claim 1 , wherein the controller is configured to adjust a frequency of the power source based on the target output power of the power transmitting apparatus.

12. The apparatus of claim 1 , wherein the power transmitting apparatus is configured to transmit power to the power receiving apparatus when the power receiving apparatus is mounted to an electric vehicle.

13. The apparatus of claim 1 , wherein the power transmitting apparatus is configured to transmit power to the power receiving apparatus when the electrical load comprises one or more batteries of an electric vehicle.

14. A method comprising:

wirelessly transferring power from a power transmitting apparatus to a power receiving apparatus connected to an electrical load;

receiving a first electrical signal comprising information about a voltage waveform associated with impedance matching circuitry of a power source of the power transmitting apparatus;

receiving a second electrical signal comprising information about a current waveform associated with the impedance matching circuitry of the power source;

determining a phase difference between the first and second electrical signals;

determining whether the phase difference is within an allowable range of phase differences;

adjusting an impedance of a circuit of the power transmitting apparatus if the phase difference is outside the allowable range of phase differences; and

adjusting at least one of a phase, a duty cycle, and a bus voltage of an amplifier of the power source if the phase difference is within the allowable range of phase differences to drive the power transmitting apparatus toward a target output power.

15. The method of claim 14 , further comprising adjusting a frequency of a component of the power source based on the target output power of the power transmitting apparatus.

16. The method of claim 14 , further comprising adjusting at least one of an inductor and a capacitor of the circuit based on the phase difference to adjust the impedance of the circuit.

17. The method of claim 14 , comprising adjusting the impedance of the circuit to minimize the phase difference.