Power transmission apparatus for detecting relative position of resonators based on a coupling coefficient

• US 9,941,753 B2
• Filed: 12/10/2014
• Issued: 04/10/2018
• Est. Priority Date: 12/19/2013
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Management Co., Ltd. (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Intellectual Property Management Co., Ltd. (Panasonic Holdings Corporation)
• Inventors: Asanuma, Kenichi, Yamamoto, Hiroshi
• Primary Examiner(s): Amrany, Adi
• Application Number:
  US14/565,895
• Publication Number:
  US 20150180286A1
• Time in Patent Office: 1,217 Days
• Field of Search: 307104
• CPC Class Codes: G01B 2210/58 Wireless transmission of information between a sensor or probe and a control or evaluation unit
• CPC Class Codes: G01B 7/003 for measuring position, not involving coordinate determination coordinate measuring G01B7/004
• CPC Class Codes: G01R 27/2611 Measuring inductance
• 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: H02J 7/00304 Overcurrent protection

Abstract

A power transmission apparatus oscillates alternating current power at a first frequency (f1) which is lower than a resonant frequency (fr) of the second resonator and at a second frequency (f2) which is higher than the resonant frequency (fr). The power transmission apparatus measures an inductance value Lin (f1) and an inductance value Lin (f2). The inductance value Lin (f1) is measured when the oscillation circuit oscillates alternating current power at the first frequency (f1), and the inductance value Lin (f2) is measured when the oscillation circuit oscillates alternating current power at the second frequency (f2). The power transmission apparatus calculates a coupling coefficient k by using an expression represented by k²=1−Lin(f2)/Lin(f1), to detect relative position of the second resonator to the first resonator on the basis of the coupling coefficient k.

Claims

1. A power transmission apparatus having a first resonator and detecting a position of a power reception apparatus that includes a load and a second resonator, the first resonator including a first coil, the second resonator including a parallel resonance circuit having a second coil and a capacitor, the power transmission apparatus comprising:

an oscillation circuit that oscillates alternating current power at a first frequency (f1) which is lower than a resonant frequency (fr) of the second resonator and oscillates alternating current power at a second frequency (f2) which is higher than the resonant frequency (fr); and

a measuring circuit, which in operation;

measures inductance values of the first resonator when the first resonator is electromagnetically coupled to the second resonator;

measures an inductance value Lin (f1) when the oscillation circuit oscillates alternating current power at the first frequency (f1), an inductance value Lin (f2) when the oscillation circuit oscillates alternating current power at the second frequency (f2);

calculates a coupling coefficient k by using an expression represented by k²=1−

Lin(f2)/Lin(f1); and

detects a relative position of the second resonator to the first resonator using the coupling coefficient k.

2. The power transmission apparatus according to claim 1, further comprises a control circuit, which in operation:

causes the power transmission apparatus to wirelessly transmit power to the power reception apparatus by using a power transmission frequency; and

causes the measuring circuit to detect the relative position of the second resonator to the first resonator by using the first frequency (f1) and the second frequency (f2).

3. The power transmission apparatus according to claim 2, further comprising a third resonator that includes a third coil used for wirelessly transmitting power from the power transmission apparatus to the power reception apparatus, the third coil being distinct from the first coil,

wherein the control circuit controls the oscillation circuit to switch from the first frequency (f1) or the second frequency (f2) oscillated by the oscillation circuit to the power transmission frequency oscillated by the power transmission circuit, and wirelessly transmit the power from the power transmission apparatus to the power reception apparatus through the power transmission circuit.

4. The power transmission apparatus according to claim 3, wherein, after the control circuit stops the oscillation by the oscillation circuit of the alternating current power and controls the first resonator to release energy stored in the first resonator to a ground, the control circuit causing the measuring circuit to detect the relative position of the second resonator to the first resonator.

5. The power transmission apparatus according to claim 2, wherein, upon detecting that the relative position of the second resonator to the first resonator is a position at which the power transmission apparatus is able to wirelessly transmit power to the power reception apparatus, the control circuit controls the oscillation circuit switch the first frequency (f1) or the second frequency (f2) to the power transmission frequency and causes the power transmission apparatus to wirelessly transmit power to the power reception apparatus.

6. The power transmission apparatus according to claim 2, further comprising:

a power transmission circuit that supplies the power to the first coil,

wherein the control circuit controls the power transmission circuit and the oscillation circuit in accordance with the inductance value Lin (f1) and the inductance value Lin (f2) measured by the measuring circuit to determine the power transmission frequency and a power transmission voltage of the wirelessly transmitting power.

7. The power transmission apparatus according to claim 2, further comprising:

a display element,

wherein the control circuit causes the display element to perform a display regarding when the coupling coefficient k exceeds a predetermined value.

8. The power transmission apparatus according to claim 2, wherein:

the power reception apparatus further includes a display unit; and

when the coupling coefficient k exceeds a predetermined value, the control circuit sends a control command to the power reception apparatus, the control command causing the display unit to display information indicating that the power reception apparatus is located in an area where the power reception apparatus is able to receive the power from the power transmission apparatus.

9. The power transmission apparatus according to claim 1, wherein, when the second coil short-circuits, the inductance value Lin (f1) corresponding to the first frequency (f1) substantially coincides with the inductance value Lin (f2) corresponding to the second frequency (f2).

10. The power transmission apparatus according to claim 1, wherein, after the oscillation circuit switches the first frequency (f1) to the second frequency (f2) or switches the second frequency (f2) to the first frequency (f1), the measuring circuit starts monitoring an amplitude of a voltage or an amplitude of a current of the oscillated alternating current power, and

when the amplitude of the voltage to the amplitude of the current converges to a fixed width, the measuring circuit measures the inductance values Lin (f1) and the inductance values Lin (f2).

11. The power transmission apparatus according to claim 1, further comprising:

a power transmission circuit that wirelessly transmits power from the power transmission apparatus to the power reception apparatus by using a power transmission frequency and a control circuit that controls the power transmission circuit to wirelessly transmit power from the power transmission apparatus to the power reception apparatus or that causes the measuring circuit to detect the relative position of the second resonator to the first resonator by using the first frequency (f1) and the second frequency (f2).

12. The power transmission apparatus according to claim 11, wherein:

the first coil is used for wirelessly transmitting power; and

the power transmission apparatus further comprises a switch for switching electrical connection between the oscillation circuit and the first coil, the switch disconnecting the electrical connection between the oscillation circuit and the first coil when the power is wirelessly transmitted.

13. A wireless power transfer system comprising:

the power transmission apparatus according to claim 1; and

the power reception apparatus.