Off-resonance frequency operation for power transfer in a loosely coupled air core transformer

• US 8,310,202 B2
• Filed: 08/17/2010
• Issued: 11/13/2012
• Est. Priority Date: 08/17/2010
• Status: Active Grant

• Current Assignee: UT-Battelle LLC
• Original Assignee: UT-Battelle LLC
• Inventors: Scudiere, Matthew B.
• Primary Examiner(s): Fantu, Yalkew
• Application Number:
  US12/858,070
• Publication Number:
  US 20120043930A1
• Time in Patent Office: 819 Days
• Field of Search: 320/108
• US Class Current: 320/108
• 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 7/00712 the cycle being controlled or terminated in response to electric parameters
• CPC Class Codes: H02M 3/3376 with automatic control of output voltage or current

Abstract

A power transmission system includes a loosely coupled air core transformer having a resonance frequency determined by a product of inductance and capacitance of a primary circuit including a primary coil. A secondary circuit is configured to have a substantially same product of inductance and capacitance. A back EMF generating device (e.g., a battery), which generates a back EMF with power transfer, is attached to the secondary circuit. Once the load power of the back EMF generating device exceeds a certain threshold level, which depends on the system parameters, the power transfer can be achieved at higher transfer efficiency if performed at an operating frequency less than the resonance frequency, which can be from 50% to 95% of the resonance frequency.

Claims

1. An apparatus for inductively transmitting power to a back EMF generating device, said apparatus comprising:

a loosely coupled air core transformer including a primary coil in a primary circuit and a secondary coil in a secondary circuit, wherein said primary coil has a first resonance frequency determined by a product of a primary inductance and a primary capacitance in said primary circuit;

an alternating current (AC) voltage supply that supplies alternating voltage at an operating frequency less than said first resonance frequency; and

the back EMF generating device electrically coupled to said secondary coil.

2. The apparatus of claim 1, wherein said back EMF generating device is a chargeable battery.

3. The apparatus of claim 1, wherein said back EMF generating device is physically connected to said secondary circuit.

4. The apparatus of claim 3, wherein said back EMF generating device is connected to said secondary coil in a parallel connection with a capacitor.

5. The apparatus of claim 4, wherein said back EMF generating device is connected to said secondary coil in a series connection with a diode configured to allow a unidirectional flow of current into said back EMF generating device.

6. The apparatus of claim 1, wherein said secondary coil has a second resonance frequency determined by a product of a secondary inductance and a secondary capacitance in said secondary circuit, wherein said secondary inductance is matched to said primary inductance.

7. The apparatus of claim 1, wherein said operating frequency is between 60% and 90% of said first resonance frequency.

8. The apparatus of claim 7, wherein said operating frequency is between 65% and 85% of said first resonance frequency.

9. The apparatus of claim 1, wherein said alternating current voltage supply comprises an H-bridge circuit including four insulated gate bipolar transistors.

10. The apparatus of claim 1, wherein said first resonance frequency is from 1 kHz to 1 MHz.

11. The apparatus of claim 1, wherein said back EMF generating device has a maximum load power in a range from 10 W to 100 kW.

12. The apparatus of claim 1, wherein said primary circuit and said secondary circuit are located in two separate structures, of which at least one is movable.

13. The apparatus of claim 12, wherein a first structure including said primary circuit is stationary, and a second structure including said secondary circuit is movable.

14. The apparatus of claim 12, wherein a first structure including said primary circuit is movable, and a second structure including said secondary circuit is movable.

15. The apparatus of claim 12, wherein said second structure is a vehicle configured to move on a road, in off-road terrain on land, on water, in water, or in air.

16. The apparatus of claim 1, wherein said primary circuit is configured to generate alternating voltage at a frequency greater than 1 kHz from an alternating current power supply that operates at a frequency from 50 Hz to 60 Hz and at a voltage from 110 V to 220V.

17. The apparatus of claim 1, wherein said loosely coupled air core transformer is designed to operate with a spacing between said primary coil and a secondary coil that is in a range from 1 mm to 36 inches.

35. The apparatus of claim 1, wherein said operating frequency is between 50% and 95% of said first resonance frequency.

18. A method of inductively transmitting power to a back EMF generating device comprising:

providing an apparatus including a loosely coupled air core transformer including a primary coil in a primary circuit and a secondary coil in a secondary circuit, wherein said primary coil has a first resonance frequency determined by a product of a primary inductance and a primary capacitance in said primary circuit; and

applying alternating voltage at an operating frequency less than said first resonance frequency to said primary coil, wherein electrical power is transmitted to a back EMF generating device electrically coupled to said secondary coil through said loosely coupled air core transformer.

19. The method of claim 18, wherein said back EMF generating device is a chargeable battery.

20. The method of claim 18, wherein said back EMF generating device is physically connected to said secondary circuit.

21. The method of claim 20, wherein said back EMF generating device is connected to said secondary coil in a parallel connection with a capacitor.

22. The method of claim 21, wherein said back EMF generating device is connected to said secondary coil in a series connection with a diode configured to allow a unidirectional flow of current into said back EMF generating device.

23. The method of claim 18, wherein said secondary coil has a second resonance frequency determined by a product of a secondary inductance and a secondary capacitance in said secondary circuit, wherein said secondary inductance is matched to said primary inductance.

24. The method of claim 18, wherein said operating frequency is between 60% and 90% of said first resonance frequency.

25. The method of claim 24, wherein said operating frequency is between 65% and 85% of said first resonance frequency.

26. The method of claim 18, wherein said alternating current voltage supply comprises an H-bridge circuit including four insulated gate bipolar transistors.

27. The method of claim 18, wherein said first resonance frequency is from 1 kHz to 1 MHz.

28. The method of claim 18, wherein said back EMF generating device has a maximum load power in a range from 10 W to 100 kW.

29. The method of claim 18, wherein said primary circuit and said secondary circuit are located in two separate structures, of which at least one is movable.

30. The method of claim 29, wherein a first structure including said primary circuit is stationary, and a second structure including said secondary circuit is movable, and said method includes placing said second structure in proximity to said first structure without causing a physical contact between said primary coil and said secondary coil.

31. The method of claim 29, wherein a first structure including said primary circuit is movable, and a second structure including said secondary circuit is movable, and said method includes moving said first structure and said second structure in proximity to each other without causing a physical contact between said primary coil and said secondary coil.

32. The method of claim 29, wherein said second structure is a vehicle configured to move on a road, in off-road terrain on land, on water, in water, or in air.

33. The method of claim 18, further comprising electrically connecting said primary circuit to an alternating current power supply that operates at a frequency from 50 Hz to 60 Hz and at a voltage from 110 V to 220V.

34. The method of claim 18, further comprising positioning said primary coil and said secondary coil such that a spacing between said primary coil and a secondary coil that is in a range from 1 mm to 36 inches.

36. The method of claim 18, wherein said operating frequency is between 50% and 95% of said first resonance frequency.