Inductive Power Transfer System

• US 20150207334A1
• Filed: 05/31/2013
• Published: 07/23/2015
• Est. Priority Date: 08/24/2012
• Status: Active Grant

• Current Assignee: Drayson Technologies (Europe) Limited
• Original Assignee: Drayson Wireless Limited
• Inventors: Mitcheson, Paul, Lucyszyn, Stepan, Pinuela Rangel, Manuel, Yates, David
• Granted Patent: US 9,899,877 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 31/66 Testing of connections, e.g. of plugs or non-disconnectable joints testing for incorrect line connections G01R31/55
• CPC Class Codes: H01F 38/14 Inductive couplings for wireless supply or distribution of electric power using inductive coupling H02J50/10
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02J 50/90 involving detection or optimisation of position, e.g. alignment
• CPC Class Codes: H02M 7/4815 Resonant converters H02M7/4811 and H02M7/4826 take precedence
• CPC Class Codes: H02M 7/537 using semiconductor devices only, e.g. single switched pulse inverters
• CPC Class Codes: H03F 3/2176 Class E amplifiers
• 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

An inductive power transfer system comprises a transmitter coil TX and a receiver coil RX spaced from the transmitter coil. A transmitter circuit comprises the transmitter coil and is in the form of a Class E amplifier with a first inductor U_choke and a transistor in series between the terminals of a power supply, a first transmitter capacitor C_par in parallel with the transistor between the first inductor and a power supply terminal, a primary tank circuit in parallel with the first transmitter capacitor, the primary tank circuit comprising the transmitter coil and a second transmitter capacitor C_res arranged in parallel with the transmitter coil, and a third transmitter capacitor C_ser in series with the first inductor between the first transmitter capacitor and the primary tank circuit. The transistor is arranged to switch at a first frequency ω_d and the capacitance of the second transmitter capacitor is selected such that the resonant frequency ω_OTX of the primary tank circuit is greater than the first frequency. The receiver circuit comprises a Class E rectifier having a first receiver capacitor C_L arranged in parallel with a load R_L and a secondary tank circuit in parallel with the first receiver capacitor. The secondary tank circuit comprises the receiver coil and a second receiver capacitor C_res arranged in parallel or series with the receiver coil. A first diode D_r2 is provided between the secondary tank circuit and the first receiver capacitor. The capacitance of the second receiver capacitor is selected such that the resonant frequency ω_oRX of the secondary tank circuit differs from the first frequency, so that the secondary tank circuit operates in semi-resonance and maintains some reactive impedance. The transmitter circuit is configured to vary the first frequency, in order to achieve a desired impedance of the primary tank circuit.

Claims

1. An inductive power transfer system comprising:

a transmitter circuit comprising a transmitter coil; and

a receiver circuit comprising the a receiver coil spaced from the transmitter coil,

wherein the transmitter circuit is in the form of a Class E amplifier comprising;

a first inductor and a transistor in series between the terminals of a power supply, the transistor being arranged to switch at a first frequency;

a first transmitter capacitance in parallel with the transistor between the first inductor and a power supply terminal;

a primary tank circuit in parallel with the first transmitter capacitance, the primary tank circuit comprising the transmitter coil and a second transmitter capacitance arranged in parallel or series with the transmitter coil;

a third transmitter capacitance in series with the first inductor between the first transmitter capacitance and the primary tank circuit,

wherein the second transmitter capacitance is selected such that the resonant frequency of the primary tank circuit is not equal to the first frequency.

2. An inductive power transfer system as claimed in claim 1, wherein the second transmitter capacitance is arranged in parallel with the transmitter coil, and wherein the second transmitter capacitance is selected such that the resonant frequency of the primary tank circuit is greater than the first frequency.

3. An inductive power transfer system as claimed in claim 1, wherein the second transmitter capacitance is arranged in series with the transmitter coil, and wherein the the second transmitter capacitance is selected such that the resonant frequency of the primary tank circuit is less than the first frequency.

4. An inductive power transfer system as claimed in claim 2, wherein the ratio of the first frequency to the resonant frequency of the primary tank circuit is greater than or equal to 0.5 and less than 1.

5. An inductive power transfer system as claimed in claim 3, wherein the ratio of the first frequency to the resonant frequency of the primary tank circuit is greater than 1 and less than or equal to 1.5.

6. An inductive power transfer system as claimed in claim 1, wherein the receiver circuit has a resonant frequency and the transmitter circuit is configured to vary the first frequency in order to achieve a desired effective impedance of the primary tank circuit.

7. An inductive power transfer system as claimed in claim 1, wherein at least one of the transmitter coil and the receiver coil has an air core.

8. An inductive power transfer system as claimed in claim 1, wherein at least one of the transmitter coil and the receiver coil has a diameter of at least 5 cm.

9. An inductive power transfer system as claimed in claim 1, wherein the spacing between the transmitter coil and the receiver coil, in use, is at least 15 cm.

10. An inductive power transfer system as claimed in claim 1, wherein the transistor is a MOSFET.

11. An inductive power transfer system as claimed in claim 1, wherein the first frequency is at least 80 kHz.

12. An inductive power transfer system as claimed in claim 1, wherein the power transferred between the transmitter coil and the receiver coil is at least 1 watt.

13. An inductive power transfer system as claimed in claim 1, wherein the receiver circuit comprises a Class E rectifier.

14. An inductive power transfer system as claimed in claim 13, wherein:

the receiver circuit comprises a first receiver capacitance and a secondary tank circuit in parallel with the first receiver capacitance;

the receiver circuit is arranged to receive a load in parallel with the first receiver capacitance; and

capacitance arranged in parallel with the receiver coil, and a first diode is provided between the secondary tank circuit and the first receiver capacitance.

15. An inductive power transfer system as claimed in claim 14, wherein the second receiver capacitance is selected such that the resonant frequency of the secondary tank circuit differs from the first frequency, whereby the secondary tank circuit operates in semi-resonance and maintains some reactive impedance.

16. An inductive power transfer system as claimed in claim 15, wherein the ratio of the first frequency to the resonant frequency of the secondary tank circuit is in the range 0.2 to 3.

17. An inductive power transfer system as claimed in claim 13, wherein the only inductor in the receiver circuit is the receiver coil.

18. An inductive power transfer system as claimed in claim 14, wherein the receiver circuit comprises at least a second diode in parallel with the first diode.

19. An inductive power transfer system as claimed in claim 13, wherein the Class E rectifier comprises at least one diode and the only capacitance in parallel with the at least one diode is provided by junction capacitance of the at least one diode(s).

20. An inductive power transfer system as claimed in claim 13, wherein the Class E rectifier comprises at least one diode and the at least one diode is a silicon carbide diode, gallium nitride diode or is formed of another wide band gap material.

46. An inductive power transfer system as claimed in claim 8, wherein at least one of the transmitter coil and the receiver coil has a diameter of at least 10 cm.

47. An inductive power transfer system as claimed in claim 11, wherein the first frequency is at least 1 MHz.

48. An inductive power transfer system as claimed in claim 12, wherein the power transferred between the transmitter coil and the receiver coil is at least 10 watts.

49. An inductive power transfer system as claimed in claim 1, wherein the first transmitter capacitance is formed of the output capacitance of the transistor.

21. (canceled)

22. (canceled)

23. A receiver circuit for use in an inductive power transfer system, the receiver circuit comprising a receiver coil and being in the form of a Class E rectifier comprising a first receiver capacitance arranged in parallel with a load and a secondary tank circuit in parallel with the first receiver capacitance, wherein the secondary tank circuit comprises the receiver coil and a second receiver capacitance arranged in parallel with the receiver coil, and a first diode is provided between the secondary tank circuit and the first receiver capacitance.

24. A receiver circuit as claimed in claim 23, wherein the receiver circuit is for use with a transmitter circuit comprising a transistor arranged to switch at a first frequency and wherein the second receiver capacitance in the receiver is selected such that the resonant frequency of the secondary tank circuit differs from the first frequency, whereby the secondary tank circuit operates in semi-resonance and maintains some reactive impedance.

25. A receiver circuit as claimed in claim 24, wherein the ratio of the first frequency to the resonant frequency of the secondary tank circuit is in the range 0.2 to 3.

26. A receiver circuit as claimed in claim 23, wherein the only inductor in the receiver circuit is the receiver coil.

27. A receiver circuit as claimed in claim 23, wherein the receiver circuit comprises at least a second diode in parallel with the first diode.

28. A receiver circuit as claimed in claim 23, wherein the Class E rectifier comprises at least one diode and the only capacitance in parallel with the at least one diode is provided by junction capacitance of the at least one diode.

29. A receiver circuit as claimed in claim 23, wherein the Class E rectifier comprises at least one diode and the at least one diode is a silicon carbide diode, gallium nitride diode or is formed of another wide band gap material.

30. A receiver circuit as claimed in claim 23, wherein the receiver coil has an air core.

31. A receiver circuit as claimed in claim 23, wherein the receiver coil has a diameter of at least 5 cm.

32. A receiver circuit as claimed in claim 23, wherein the receiver coil has a diameter of at least 10 cm.

33. A transmitter for use in an inductive power transfer system, the transmitter circuit comprising a transmitter coil and being in the form of a Class E amplifier comprising:

a first inductor and a transistor in series between the terminals of a power supply, the transistor being arranged to switch at a first frequency;

a first transmitter capacitance in parallel with the transistor between the first inductor and a power supply terminal;

a primary tank circuit in parallel with the first transmitter capacitance, the primary tank circuit comprising the transmitter coil and a second transmitter capacitance arranged in parallel or series with the transmitter coil;

a third transmitter capacitance in series with the first inductor between the first transmitter capacitance and the primary tank circuit,

wherein the second transmitter capacitance is selected such that the resonant frequency of the primary tank circuit is not equal to the first frequency.

34. A transmitter circuit as claimed in claim 33, wherein the second transmitter capacitance is arranged in parallel with the transmitter coil, and wherein the second transmitter capacitance is selected such that the resonant frequency of the primary tank circuit is greater than the first frequency.

35. A transmitter circuit as claimed in claim 33, wherein the second transmitter capacitance is arranged in series with the transmitter coil, and wherein the second transmitter capacitance is selected such that the resonant frequency of the primary tank circuit is less than the first frequency.

36. A transmitter circuit as claimed in claim 34, wherein the ratio of the first frequency to the resonant frequency of the primary tank circuit is greater than or equal to 0.5 and less than 1.

37. A transmitter circuit as claimed in claim 35, wherein the ratio of the first frequency to the resonant frequency of the primary tank circuit is greater than 1 and less than or equal to 1.5.

38. A transmitter circuit as claimed in claim 33, wherein the transmitter circuit is for use with a receiver circuit having a resonant frequency and the transmitter circuit is configured to vary the first frequency, in order to achieve a desired effective impedance of the primary tank circuit.

39. A transmitter circuit as claimed in claim 33, wherein the transmitter coil has an air core.

40. A transmitter circuit as claimed in claim 33, wherein the transmitter coil has a diameter of at least 5 cm.

41. A transmitter circuit as claimed in claim 40, wherein the transmitter coil has a diameter of at least 10 cm.

42. A transmitter circuit as claimed in claim 33, wherein the transistor is a MOSFET.

43. A transmitter circuit as claimed in claim 33, wherein the first frequency is at least 80 kHz.

44. A transmitter circuit as claimed in claim 43, wherein the first frequency is at least 1 MHz.

45. A transmitter circuit as claimed in claim 33, wherein the first transmitter capacitance is formed of the output capacitance of the transistor.