Wireless power transfer system

• US 10,170,940 B2
• Filed: 05/04/2016
• Issued: 01/01/2019
• Est. Priority Date: 05/04/2016
• Status: Active Grant

• Current Assignee: Imperial College Innovations Ltd. (Imperial College London)
• Original Assignee: Imperial Innovations Limited (Imperial College London)
• Inventors: Mitcheson, Paul, Yates, David, Aldhaher, Samer
• Primary Examiner(s): Skibinski, Thomas
• Application Number:
  US15/146,851
• Publication Number:
  US 20170324277A1
• Time in Patent Office: 972 Days
• Field of Search: 307104, 307 91, 323351
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02M 7/537 using semiconductor devices only, e.g. single switched pulse inverters
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A load-independent Class EF inverter may maintain ZVS operation, and produce a constant output current, rather than a constant output voltage, regardless of the load resistance. A constant output current allows the inverter to operate efficiently for a load range from zero resistance (short circuit) to a certain maximum load resistance, making the inverter more suitable as a coil driver for an IPT system. The resonant frequency of the resonant circuit may be tuned to a non-integer multiple of a switching frequency.

Claims

1. A power inverter for driving a transmitter coil in an inductive power transfer system, wherein the power inverter is suitable for class ‘

EF’

operation, is arranged to drive a load resistance, and comprises;

a switching device arranged between a power source and ground and arranged to switch at a switching frequency; and

a resonant network arranged in parallel with the switching device between the power source and ground, the resonant network having a resonant frequency which is a non-integer multiple of the switching frequency, such that, in operation, a substantially constant current passes through the load resistance.

2. The power inverter of claim 1, wherein a first node of the switching device is coupled to ground, a second node of the switching device is coupled via a first inductor to a DC supply voltage, and a third node of the switching device is used to switch the switching device on and off.

3. The power inverter of claim 1, wherein a first capacitor is coupled in parallel with the switching device between the power source and ground.

4. The power inverter of claim 1, wherein the resonant network comprises a resonant circuit, the resonant circuit comprising a second inductor and a second capacitor.

5. The power inverter of claim 1, wherein the load resistance comprises a resistance of the transmitter coil.

6. The power inverter of claim 1 wherein the load resistance comprises a resistance of at least one receiver coil.

7. The power inverter of claim 1 wherein a value of the load resistance can vary.

8. The power inverter of claim 1, wherein the non-integer multiple is between 1 and 2.

9. The power inverter of claim 1, wherein a third capacitor and a third inductor are coupled in series with the load resistance.

10. The power inverter of claim 1, wherein the power inverter is arranged to maintain zero-voltage-switching operation.

11. A method of fabricating a power inverter for driving a transmitter coil in an inductive power transfer system, wherein the power inverter is suitable for class ‘

EF’

operation, is arranged to drive a load resistance, and the method comprises;

arranging a switching device between a power source and ground;

arranging the switching device to switch at a switching frequency;

arranging a resonant network in parallel with the switching device between the power source and ground;

arranging the resonant network to have a resonant frequency which is a non-integer multiple of the switching frequency, such that, in operation, a substantially constant current passes through the load resistance.

12. The method of claim 11, wherein the inverter is a power inverter comprises:

a switching device arranged between a power source and ground and arranged to switch at a switching frequency; and

a resonant network arranged in parallel with the switching device between the power source and ground, the resonant network having a resonant frequency which is a non-integer multiple of the switching frequency, such that, in operation, a substantially constant current passes through the load resistance.

13. A rectifier for receiving an AC signal from a receiver coil in an inductive power transfer system, wherein the rectifier is suitable for class ‘

EF’

operation, is arranged to drive a load resistance, and comprises;

a switching device arranged between a power source and the load resistance and arranged to switch at a switching frequency; and

a resonant network having a resonant frequency which is a non-integer multiple of the switching frequency and arranged such that, in operation, a substantially constant current passes through the load resistance.

14. The rectifier of claim 13, wherein the non-integer multiple is between 1.5 and 1.65.

15. The rectifier of claim 13, wherein the power source comprises a receiver coil.

16. An inductive power transfer system comprising a transmitter circuit and a receiver circuit, the transmitter circuit comprising a power inverter and the receiver circuit comprising a rectifier;

wherein the power inverter is configured for driving a transmitter coil in the inductive power transfer system, wherein the power inverter is suitable for class ‘

EF’

operation, is arranged to drive a load resistance, and comprises;

a switching device arranged between a power source and ground and arranged to switch at a first switching frequency; and

a resonant network arranged in parallel with the switching device between the power source and ground, the resonant network having a resonant frequency which is a non-integer multiple of the first switching frequency, such that, in operation, a substantially constant current passes through the load resistance; and

wherein the rectifier is configured for receiving an AC signal from a receiver coil in the inductive power transfer system, wherein the rectifier is suitable for class ‘

EF’

operation, is arranged to drive a load resistance, and comprises;

a switching device arranged between a power source and the load resistance and arranged to switch at a second switching frequency; and

a resonant network having a resonant frequency which is a non-integer multiple of the second switching frequency and arranged such that, in operation, a substantially constant current passes through the load resistance.

17. The inductive power transfer system of claim 16, wherein respective non-integer multiples of the first switching frequency and the second switching frequency are equal.

18. The inductive power transfer system of claim 16, wherein the load resistance of the rectifier further comprises a receiver coil spaced from the transmitter coil, the receiver coil being comprised within a receiver circuit arranged to receive power via inductive power transfer from the transmitter circuit.

19. A method of fabricating a rectifier for receiving an AC signal from a receiver coil in an inductive power transfer system, wherein the rectifier is suitable for class ‘

EF’

operation, is arranged to drive a load resistance, the method comprising;

arranging a switching device between a power source and the load resistance;

arranging the switching device to switch at a switching frequency; and

arranging a resonant network having a resonant frequency which is a non-integer multiple of the switching frequency, such that, in operation, a substantially constant current passes through the load resistance.

20. The method of claim 19, wherein the non-integer multiple is equal to 1.5.