Inductive power transfer system

1. An inductive power transfer (IPT system) comprising:

a primary conductive path adapted to provide a magnetic field for reception by a pick-up device; and

an AC-AC full-bridge converter provided between the primary conductive path and an alternating current power supply to provide a controlled current to the primary conductive path for provision of the magnetic field,

wherein the primary conductive path has a frequency which is greater than a frequency of the alternating current power supply when power is being transferred to the pick-up device.

2. An IPT system as claimed in claim 1 , further comprising a controller for controlling the pick-up device to shape an input current drawn from the alternating Current power supply.

3. An IPT system as claimed in claim 2 wherein the controller modulates the pick-up device to shape the input current drawn from the alternating current power supply.

4. An IPT system as claimed in claim 2 wherein the pick-up includes a full-bridge converter having two pairs of complementary switches, and the controller controls the pick-up device by controlling a phase angle between the pairs of complementary switches.

5. An IPT system as claimed in claim 1 wherein the alternating current power supply comprises a mains utility power supply.

6. An IPT system as claimed in claim 1 wherein the IPT system comprises a bi-directional IPT system.

7. An IPT system as claimed in claim 1 , wherein the AC-AC full-bridge converter connects the primary conductive path to the alternating current power supply to provide a current to the alternating current power supply having a frequency which is less than a frequency of the current in the primary conductive path when power is being transferred to the alternating current power supply.

8. A primary circuit for an IPT system, the primary circuit comprising:

a primary conductive path adapted to provide a magnetic field for reception by a pick-up device; and

an AC-AC converter provided between the primary conductive path and an alternating current power supply,

wherein the primary conductive path has a frequency which is greater than a frequency of the alternating current power supply when is being transferred to the pick-up device.

9. A primary circuit for an IPT system as claimed in claim 8 wherein the alternating current power supply comprises a mains utility power supply.

10. A primary circuit for an IPT system as claimed in claim 8 wherein the primary circuit comprises part of a bi-directional IPT system.

11. A primary circuit for an IPT system as claimed in claim 8 wherein the AC-AC converter connects the alternating current power supply to the primary conductive path to provide a current in the primary conductive path having a frequency which is greater than a frequency of the alternating current power supply when power is being transferred to an IPT pick-up device.

12. A primary circuit for an IPT system as claimed in claim 8 wherein the AC-AC converter connects the primary conductive path to the alternating current power supply to provide a current to the alternating current power supply having a frequency which is less than a frequency of a current in the primary conductive path when power is being transferred from an IPT pick-up device to the alternating current power supply.

13. A method for controlling an inductive power transfer (IPT) system having an AC-AC full-bridge converter provided between an AC power supply and a primary conductive path, the method comprising:

controlling a pick-up device of the IPT system to shape an input current drawn from an alternating current power supply,

wherein the primary conductive path has a frequency which is greater than a frequency of the alternating current power supply when power is being transferred to the pick-up device.

14. A method as claimed in claim 13 , further comprising modulating operation of the pick-up device to shape an input current drawn from the alternating current power supply.

15. A method as claimed in claim 13 wherein the pick-up device includes a full-bridge converter having two pairs of complementary switches, and the method comprises controlling the pick-up device by controlling a phase angle between the pairs of complementary switches.

16. A method as claimed in claim 13 wherein the alternating current power supply comprises a mains utility power supply.

17. A method as claimed in claim 13 wherein the IPT system comprises a hi-directional IPT system.

18. A method as claimed in claim 13 , further comprising controlling the AC-AC full-bridge converter to connect the alternating current power supply to the primary conductive path to provide a current in the primary conductive path having a frequency which is greater than a frequency of the alternating current power supply when power is being transferred to the pick-up device.

19. A method as claimed in claim 13 , further comprising controlling the AC-AC full-bridge converter to connect the primary conductive path to the alternating current power supply to provide a current to the alternating current power supply having a frequency which is less than a frequency of a current in the primary conductive path when power is being transferred to the alternating current power supply.