Efficiency non-self tuning wireless power transfer systems

1. A wireless power transfer primary resonant network including:

a primary winding capable of being energised to provide a magnetic field; and

at least one reactive tuning component selected to constrain a reactive loading on a power supply which energises the primary resonant network, the reactive tuning component being selected dependent on a given variation in inductance or capacitance of the primary resonant network and a given variation in inductance or capacitance of a secondary resonant network to be coupled to the primary resonant network, and wherein an input impedance to the primary resonant network is inductive.

2. The wireless power transfer primary resonant network as claimed in claim 1 wherein the reactive tuning component is selected dependent on a given variation in coupling between the primary and secondary resonant networks.

3. The wireless power transfer primary resonant network as claimed in claim 2 wherein the given variation in coupling is caused by relative movement of a pick-up winding of the secondary resonant network relative to the primary winding.

4. The wireless power transfer primary resonant network as claimed in claim 1 wherein the reactive tuning component is selected to constrain a variation in reactive loading on the power supply.

5. The wireless power transfer primary resonant network as claimed in claim 1 wherein the reactive tuning component is selected to constrain power factor.

6. The wireless power transfer primary resonant network as claimed in claim 1 wherein the reactive tuning component comprises the primary winding.

7. The wireless power transfer primary resonant network as claimed in claim 1 wherein the given variation in inductance or capacitance is caused by relative movement or displacement of a pick-up winding of the secondary resonant network relative to the primary winding.

8. A wireless power transfer secondary resonant network including:

a pick-up winding capable of receiving energy from a varying magnetic field produced by a primary resonant network; and

at least one reactive tuning component selected to constrain a reactive loading on a power supply which energises the primary resonant network, the reactive tuning component being selected dependent on a given variation in inductance or capacitance of the secondary resonant network and a given variation in inductance or capacitance of the primary resonant network to which the secondary resonant network is to be coupled, and wherein an input impedance to the primary resonant network is inductive.

9. The wireless power transfer secondary resonant network as claimed in claim 8 wherein the reactive tuning component is selected dependent on a given variation in coupling between the primary and secondary resonant networks.

10. The wireless power transfer secondary resonant network as claimed in claim 8 wherein the reactive tuning component is selected to constrain a variation in reactive loading on the power supply.

11. The wireless power transfer secondary resonant network as claimed in claim 8 wherein the reactive tuning component is selected to constrain power factor.

12. The wireless power transfer secondary resonant network as claimed in claim 8 wherein the reactive tuning component comprises the pick-up winding.

13. The wireless power transfer secondary resonant network as claimed in claim 8 wherein the given variation in inductance or capacitance is caused by relative movement or displacement of the pick-up winding relative to a primary winding of the primary resonant network.

14. The wireless power transfer secondary resonant network as claimed in claim 8 wherein the given variation in coupling is caused by relative movement of the pick-up winding relative to a primary winding of the primary resonant network.

15. An apparatus for wireless power transfer including:

a primary resonant network, and

a secondary resonant network coupled to the primary resonant network,

wherein the apparatus has a system operating frequency and one or both of the primary resonant network and the secondary resonant network have a natural resonant frequency that is different from the system operating frequency, and

wherein the natural resonant frequency of the primary resonant network is selected dependent on a given variation in inductance or capacitance of the primary resonant network and a given variation in inductance or capacitance of the secondary resonant network, and wherein the input impedance to the primary resonant network is inductive.

16. The apparatus as claimed in claim 15 wherein the natural resonant frequency of the primary resonant network is selected dependent on a given variation in coupling between the primary and secondary resonant networks.

17. The apparatus as claimed in claim 15 wherein the natural resonant operating frequency of the primary resonant network is selected to constrain a variation in the operating frequency of the primary resonant network.

18. The apparatus as claimed in claim 15 comprising a wireless power transfer charger.

19. A method of designing a wireless power transfer primary resonant network having a primary winding capable of being energised to provide a magnetic field, the method comprising:

selecting at least one reactive tuning component selected to constrain the reactive loading on a power supply which energises the primary resonant network, the reactive tuning component being selected dependent on a given variation in inductance or capacitance of the primary resonant network and a given variation in inductance or capacitance of a secondary resonant network to be coupled to the primary resonant network,

wherein the input impedance to the primary resonant network is inductive.