Wireless power transmission system and power transmission device

• US 9,595,834 B2
• Filed: 05/14/2015
• Issued: 03/14/2017
• Est. Priority Date: 05/27/2014
• 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: Yamamoto, Hiroshi, Asanuma, Kenichi, Sakata, Tsutomu, Kanno, Hiroshi
• Primary Examiner(s): Tran, Thienvu
• Assistant Examiner(s): Stables, David M
• Application Number:
  US14/711,788
• Publication Number:
  US 20150349541A1
• Time in Patent Office: 670 Days
• Field of Search: 307/104, 320/108, 320/137, 320/162
• US Class Current: 1/1
• CPC Class Codes: G01V 3/10 using induction coils
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02J 50/402 the two or more transmitting or the two or more receiving devices being integrated in the same unit, e.g. power mats with several coils or antennas with several sub-antennas
• CPC Class Codes: H02J 50/60 responsive to the presence of foreign objects, e.g. detection of living beings
• CPC Class Codes: H02J 50/70 involving the reduction of electric, magnetic or electromagnetic leakage fields

Abstract

In a first power transmission period, a power transmission device holds, in a memory, a value indicating a frequency f0 corresponding to an actual voltage value that matches a requested voltage value, then causes first AC power to be transmitted by using the frequency f0, and uses a foreign substance detector to determine whether or not a foreign substance is present. When it is determined that no foreign substance is present, in a second power transmission period, the power transmission device causes the power transmission of the first AC power to be resumed by using the value indicating the frequency f0, the value being held in the memory.

Claims

1. A power transmission device that transmits first AC power in a noncontact manner to a first resonator of a power receiving device including a power receiving circuit, the first resonator receiving the first AC power, the power receiving circuit converting the first AC power received by the first resonator to first DC power and supplying the first DC power to a load, the power transmission device comprising:

a memory that stores a requested voltage value of the first DC power supplied to the load;

a receiving circuit that receives, from the power receiving device, an actual voltage value of the first DC power supplied to the load;

an inverter that generates and transmits the first AC power to the first resonator via a second resonator;

an oscillator that generates second AC power smaller than the first AC power and transmits the second AC power to the first resonator via a third resonator;

a foreign substance detector that determines whether or not a foreign substance is present between the first resonator and the third resonator based on a physical quantity in the third resonator that changes according to the second AC power; and

power transmission control circuitry operative to;

set a foreign substance detection period in which foreign substance is detected by the foreign substance detector, between i) a first power transmission period in which the first AC power is transmitted from the second resonator to the first resonator and ii) a second power transmission period subsequent to the first power transmission period;

set sequentially to the inverter, in the first power transmission period, frequencies i) from a frequency f1 of a power transmission voltage in an initial state ii) to a frequency f2 of the requested voltage value;

cause the inverter to transmit the first AC power at each of the set frequencies;

compare the requested voltage value with the actual voltage value of each of the frequencies, received by the receiving circuit;

store a value indicating a frequency f0 of the actual voltage value in the memory if the actual voltage value equals to the requested voltage value;

cause the inverter to transmit the first AC power at the frequency f0 if the actual voltage value equals to the requested voltage value;

cause the inverter to stop the first AC power temporarily after the elapse of a predetermined period of time;

cause the foreign substance detector to determine whether or not the foreign substance is present in the foreign substance detection period; and

cause the inverter to resume a transmission of the first AC power in the second power transmission period by the value indicating the frequency f0 in the memory if it is determined that the foreign substance is not present within a predetermined period that starts from the stopping of the first AC power and that is regulated to cause the inverter to resume a transmission of the first AC power from the frequency f1.

2. The power transmission device according to claim 1,

wherein the frequency f1 is higher than the frequency f2.

3. The power transmission device according to claim 1,

wherein the frequency f1 is lower than the frequency f2.

4. The power transmission device according to claim 1,

wherein, when it is determined that the foreign substance is not present after the predetermined period, the power transmission control circuitry resumes the transmission of the first AC power at the frequency f1 in the second power transmission period.

5. The power transmission device according to claim 1,

wherein the predetermined period is 350 milliseconds specified in a Qi standard of a wireless power consortium (WPC).

6. The power transmission device according to claim 1,

wherein the power transmission control circuitry is operative to:

store, in the first power transmission period i) a value indicating a duty ratio of a voltage output from the inverter circuit and ii) the value indicating the frequency f0 in the memory;

cause the first AC power to be transmitted at the frequency f0; and

cause in the second power transmission period, the transmission of the first AC power to be resumed by using i) the value indicating the frequency f0, and ii) the value indicating the duty ratio in the memory.

7. The power transmission device according to claim 1,

wherein the foreign substance detector measures the physical quantity in the third resonator that changes according to the second AC power, and determines that a foreign substance is present between the first resonator and the third resonator when a difference between the physical quantity after having changed and a prescribed reference value is greater than a preset threshold value.

8. The power transmission device according to claim 1,

wherein the foreign substance detector measures the physical quantity in the third resonator, and determines whether or not a foreign substance is present based on a value calculated from the measured physical quantity.

9. The power transmission device according to claim 8,

wherein the physical quantity in the third resonator is i) a voltage that is applied to the third resonator, ii) a current that flows in the third resonator, iii) a frequency that is applied to the third resonator, iv) an input impedance value of the third resonator, or v) an input inductance value of the third resonator.

10. The power transmission device according to claim 1,

wherein the first resonator has a parallel resonant circuit including a coil and a capacitor, and

if the physical quantity in the third resonator is an input inductance of the third resonator,

the foreign substance detector is operative to:

measure i) an input inductance value Lin(f10) of the third resonator that is produced when the oscillator is oscillating at the frequency f10, and ii) an input inductance value Lin(f20) of the third resonator that is produced when the oscillator is oscillating at the frequency f20;

calculate a coupling coefficient k according to an expression k²=1−

Lin(f20)/Lin(f10); and

determine whether or not the foreign substance is present based on the calculated coupling coefficient k.

11. The power transmission device according to claim 1,

wherein the first resonator has a parallel resonant circuit including a coil and a capacitor, and

if the physical quantity in the third resonator is an input inductance value of the third resonator,

the foreign substance detector is operative to:

measure i) an input inductance value Lin(f10) of the third resonator that is produced when the oscillator is oscillating at the frequency f10, and ii) an input inductance value Lin(f20) of the third resonator that is produced when the oscillator is oscillating at the frequency f20;

calculate a ratio between the Lin(f10) and the Lin(f20); and

determine whether or not the foreign substance is present based on the calculated ratio.

12. The power transmission device according to claim 1,

wherein the first resonator has a parallel resonance circuit including a coil and a capacitor,

the square of an oscillation frequency of the oscillator is inversely proportional to the input inductance value of the third resonator, when the oscillator is a self-exciting oscillator and when the physical quantity in the third resonator is an input inductance value of the third resonator, and

the foreign substance detector is operative to:

measure the frequency f10 and the frequency f20 at which the oscillator is oscillating;

calculate a coupling coefficient k according to an expression k²=1−

f10²/f20²; and

determine whether or not a foreign substance is present based on the calculated coupling coefficient k.

13. The power transmission device according to claim 1,

wherein the first resonator and the third resonator are the same resonator, and

the power transmission device further comprises a switch that switches between i) a first electrical connection between the inverter and the same resonator, and ii) a second electrical connection between the oscillator and the same resonator, by the power transmission control circuitry,

wherein the power transmission control circuitry is operative to:

control the switch to switch from the first electrical connection to the second electrical connection when changing from the first power transmission period to the foreign substance detection period; and

control the switch to switch from the second electrical connection to the first electrical connection when changing from the foreign substance detection period to the second power transmission period.

14. A wireless power transmission system comprises:

a power receiving device having a first resonator and a power receiving circuit, the first resonator receiving a first AC power, the power receiving circuit converting the first AC power received by the first resonator to first DC power and supplying the first DC power to a load; and

a power transmission device that transmits first AC power in a noncontact manner to the power receiving device and that includes

a memory that stores a requested voltage value of the first DC power supplied to the load,

a receiving circuit that receives, from the power receiving device, an actual voltage value of the first DC power supplied to the load,

an inverter that generates the first AC power and transmits the first AC power to the first resonator via a second resonator,

an oscillator that generates second AC power smaller than the first AC power and transmits the second AC power to the first resonator via a third resonator,

a foreign substance detector that determines whether or not a foreign substance is present between the first resonator and the third resonator based on a physical quantity in the third resonator that changes according to the second AC power, and

a power transmission control circuitry operative to;

set a foreign substance detection period in which foreign substance is detected by the foreign substance detector, between i) a first power transmission period in which the first AC power is transmitted from the second resonator to the first resonator and ii) a second power transmission period subsequent to the first power transmission period;

set sequentially to the inverter, in the first power transmission period, frequencies (i) from a frequency f1 of a power transmission voltage in an initial state (ii) to a frequency f2 of the requested voltage value;

cause the inverter to transmit the first AC power at each of the set frequencies;

compare the requested voltage value with the actual voltage value of each of the frequencies, received by the receiving circuit;

store a value indicating a frequency f0 of the actual voltage value in the memory if the actual voltage value equals to the requested voltage value;

cause the inverter to transmit the first AC power at the frequency f0 if the actual voltage value equals to the requested voltage value;

cause the inverter to stop the first AC power temporarily after the elapse of a predetermined period of time;

cause the foreign substance detector to determine whether or not the foreign substance is present in the foreign substance detection period; and

cause the inverter to resume a transmission of the first AC power in the second power transmission period by the value indicating the frequency f0 in the memory if it is determined that the foreign substance is not present within a predetermined period that starts from the stopping of the first AC power and that is regulated to cause the inverter to resume a transmission of the first AC power from the frequency f1.