Wireless power transfer system

Abstract

To provide a wireless power transfer system that when a coupling coefficient between power transmission / reception coils is varied by a position of a power reception coil being varied, can inhibit transfer efficiency between power transmission and reception from being reduced, by compensating for the coupling coefficient between the power transmission / reception coils.SOLUTION: There is provided a wireless power transfer system comprising a power transmission coil, a power reception coil, a relay coil unit, and a frequency adjustment unit. The wireless power transfer system is configured so that the power transmission coil uses electromagnetic force to perform power transmission to the power reception coil, the relay coil unit relays the power transmission from the power transmission coil to the power reception coil, and the frequency adjustment unit adjusts a resonance frequency of the relay coil unit depending on a distance between the power transmission coil and the power reception coil.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a wireless power transmission system. [Background technology]

[0002] Conventionally, magnetic resonance coupling type wireless power transfer (WPT) has attracted attention as a technology that can transmit power contactlessly, and is expected to be used as a contactless charging method for internal medical devices, home appliances, electric vehicles, etc.

[0003] WPT has a problem in that if the position of the power receiving coil is shifted or moved away from the power transmitting coil, the coupling coefficient between the power transmitting and receiving coils decreases, and the power transmission efficiency between the power transmitting and receiving coils decreases. Non-Patent Document 1 discloses a method for improving the transmission efficiency by inserting a repeater coil having the same resonant frequency as the resonant frequency of the power transmitting and receiving coils between the power transmitting and receiving coils to compensate for the coupling coefficient between the power transmitting and receiving coils when the transmission efficiency decreases due to the increase in the distance between the power transmitting and receiving coils. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] JinWook Kim and 3 others, "Efficiency analysis of magnetic resonance wireless power transfer with intermediate resonant coil", IEEE Antennas and Wireless Propagation Letters, Vol. 10, pp. 389-392, 2011. Summary of the Invention [Problem to be solved by the invention]

[0005] However, since the improvement in transmission efficiency by the repeater coil depends on the positional relationship between the repeater coil and the transmitting and receiving coils, if the position of the receiving coil shifts or moves away from its designated position, as in the past, it is not possible to compensate for the decreased coupling coefficient between the transmitting and receiving coils, and there is a risk that the decrease in transmission efficiency between the transmitting and receiving coils cannot be suppressed.

[0006] The present invention has been made in consideration of the above circumstances, and provides a WPT system that can suppress a decrease in transmission efficiency between transmitting and receiving coils by compensating for the coupling coefficient between the transmitting and receiving coils, even if the position of the receiving coil changes and the coupling coefficient between the transmitting and receiving coils changes. [Means for solving the problem]

[0007] According to the present invention, the following inventions are provided. [1] A wireless power transmission system comprising a power transmitting coil, a power receiving coil, a relay coil unit, and a frequency adjustment unit, wherein the power transmitting coil transmits power to the power receiving coil by using electromagnetic force, the relay coil unit relays power transmitted from the power transmitting coil to the power receiving coil, and the frequency adjustment unit is configured to adjust a resonant frequency of the relay coil unit in accordance with a distance between the power transmitting coil and the power receiving coil. [2] A wireless power transmission system as described in [1], wherein the frequency adjustment unit is configured to adjust the resonant frequency of the relay coil unit by changing the capacitance of a capacitor connected to a relay coil provided in the relay coil unit. [3] A wireless power transmission system as described in [1] or [2], wherein the relay coil unit is arranged horizontally with the power transmission coil and at least partially overlaps with the power transmission coil in the axial direction. [4] A wireless power transmission system according to any one of [1] to [3], wherein the relay coil unit includes a first and a second relay coil arranged on the same plane, the inner diameter of the second relay coil being larger than the outer diameter of the first relay coil and being arranged outside the first relay coil. [5] A wireless power transmission system according to any one of [1] to [4], wherein the relay coil unit includes a relay coil arranged on the same plane as the power transmission coil, an inner diameter of the relay coil being larger than an outer diameter of the power transmission coil, and the relay coil being arranged outside the power transmission coil. [6] The wireless power transmission system according to any one of [1] to [5], wherein the relay coil unit includes a plurality of relay coils, each of which is disposed on the same plane. [7] A wireless power transmission system according to any one of [1] to [6], wherein the relay coil unit is arranged so as to face the direction of a magnetic field generated from the power transmitting coil to the power receiving coil and outside the width of the power transmitting coil. Effect of the Invention

[0008] In the WPT system of the present invention, the resonant frequency of the relay coil unit is configured to be adjustable according to the distance between the transmitting coil and the receiving coil. Therefore, even if the position of the receiving coil changes and the coupling coefficient between the transmitting and receiving coils changes, the coupling coefficient between the transmitting and receiving coils can be compensated for to suppress a decrease in the transmission efficiency between the transmitting and receiving coils. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic block diagram showing a configuration of a WPT system 100 according to a first embodiment of the present invention. [Diagram 2] 1 is a schematic perspective view of a WPT system 100 according to a first embodiment of the present invention. [Diagram 3]1 is a schematic perspective view of a WPT system 100 according to a first embodiment of the present invention. [Figure 4] 13 is a diagram showing the magnetic field distribution of the WPT system 100 when the resonant frequency f2 of the relay coil is higher than the resonant frequency f1 of the power transmission coil 11a. FIG. [Diagram 5] 13 is a diagram showing the magnetic field distribution of the WPT system 100 when the resonant frequency f2 of the relay coil is lower than the resonant frequency f1 of the power transmission coil 11a. FIG. [Figure 6] FIG. 11 is a schematic perspective view of a WPT system 100 according to a second embodiment of the present invention. [Figure 7] FIG. 11 is a schematic perspective view of a WPT system 100 according to a third embodiment of the present invention. [Figure 8] FIG. 11 is a schematic perspective view of a WPT system 100 according to a fourth embodiment of the present invention. [Figure 9] FIG. 11 is a schematic top view of a WPT system 100 according to a fifth embodiment of the present invention. [Figure 10] FIG. 11 is a schematic top view of a WPT system 100 according to a fifth embodiment of the present invention. [Figure 11] FIG. 13 is a measurement diagram for the horizontal arrangement. [Figure 12] FIG. 13 is a measurement diagram for the vertical arrangement. [Figure 13] 13 is a graph showing the transmission efficiency when the resonant frequency f2 of the relay coil in a horizontal arrangement is changed. [Figure 14] 13 is a graph showing the coupling coefficient when the resonant frequency f2 of the relay coil in a horizontal arrangement is changed. [Figure 15] 13 is a graph showing the transmission efficiency when the resonant frequency f2 of the relay coil in a vertical arrangement is changed. [Figure 16] 13 is a graph showing the coupling coefficient when the resonant frequency f2 of the relay coil in a vertical arrangement is changed. [Figure 17] 13 is a graph showing the transmission efficiency when the distance D1 between the power transmitting and receiving coils in a horizontal arrangement is changed. [Figure 18]13 is a graph showing the transmission efficiency when the distance D1 between the power transmitting and receiving coils in a vertical arrangement is changed. [Figure 19] 13 is a graph showing the transmission efficiency when the distance D2 between the relay coils in a vertical arrangement is changed. [Figure 20] FIG. 13 is a schematic top view of an experiment on the change in transmission efficiency due to a misalignment X of the receiving coil. [Figure 21] 13 is a graph showing the transmission efficiency when the displacement X of the receiving coil is changed. [Figure 22] 13 is a graph showing a coupling coefficient when a displacement X of the receiving coil is changed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described. Various features shown in the following embodiments can be combined with each other. Also, each feature can be an invention independently.

[0011] 1. First embodiment

[0012] The WPT system according to one embodiment of the present invention includes a power transmitting coil 11a, a power receiving coil 21, a relay coil unit 12, and a frequency adjuster 14b.

[0013] In this embodiment, a system including a power transmitting device 10, a power receiving device 20, and a sensor device 30 will be described as an example of a WPT system 100 (FIG. 1). The power transmitting device 10 includes a power transmitting coil 11a, a relay coil unit 12, and a frequency adjustment unit 14b, and the power receiving device 20 includes a power receiving coil 21.

[0014] In the following description, up, down, left, right, front and rear directions are defined as shown in Figs. 2 and 9, and the left and right linear directions are defined as axial directions.

[0015] 1.1 Power transmission device 10 The power transmitting device 10 includes a power transmitting section 11, a relay coil unit 12, a communication section 13, and a control section 14. The power transmitting device 10 transmits power to a power receiving coil 21 of a power receiving device 20 by utilizing electromagnetic force. The power transmitting device 10 can be installed on the ground or the like to transmit power to, for example, an electric vehicle which is the power receiving device 20.

[0016] 1.1.1 Power transmission section 11 The power transmission unit 11 includes a power transmission coil 11a, a power supply loop coil 11b, and a power source 11c. The power transmission coil 11a is a coil for transmitting power to a power receiving coil 21 of the power receiving device 20 by utilizing electromagnetic force. The power transmission coil 11a is supplied with power from a power supply loop coil 11b connected to the power source 11c. The power transmission coil 11a can be a spiral coil or a solenoid coil. The resonant frequency of the power transmission coil 11a is the same as the resonant frequency of the power receiving coil 21. The power source 11c is an AC power source that outputs high frequency waves.

[0017] 1.1.2 Relay coil unit 12 The relay coil unit 12 relays power transmission from the power transmitting coil 11a to the power receiving coil 21 of the power receiving device 20. The relay coil unit 12 can include one or more relay coils, but includes one relay coil 12a in the example shown in Fig. 2. The relay coil 12a can be a spiral coil or a solenoid coil. A variable capacitor (not shown) is connected to the relay coil 12a, and the resonant frequency f2 of the relay coil 12a is adjusted by changing the capacitance of the variable capacitor.

[0018] The relay coil unit 12 according to this embodiment is disposed horizontally with the power transmission coil 11a and at least partially overlaps with the power transmission coil 11a in the axial direction (FIG. 2). The power transmission coil 11a and the relay coil unit 12 are fixed in position.

[0019] 3 shows an example of a case where the relay coil unit 12 includes multiple relay coils 12a, 12b, and 12c. It is preferable that the relay coil 12a adjacent to the power transmitting coil 11a at least partially overlaps with the power transmitting coil 11a in the axial direction, and each of the relay coils 12a, 12b, and 12c is arranged horizontally with the power transmitting coil 11a so as to at least partially overlap with the adjacent relay coil in the axial direction. With this configuration, the transmission distance from the power transmitting coil 11a to the power receiving coil 21 can be extended.

[0020] 1.1.3 Communication section 13 The communication unit 13 is configured to be able to communicate various information required for power transmission with the sensor device 30. For example, the communication unit 13 can receive distance information between the power transmitting coil 11a and the receiving coil from a communication unit 32 of the sensor device 30, which will be described later. Note that in the present invention, distance includes not only the distance in the left-right direction (axial direction) but also the distance in the front-rear and up-down directions. The communication unit 13 can output the information received from the sensor device 30 to the control unit 14. The communication unit 13 may be configured to be able to communicate with the power receiving device 20.

[0021] 1.1.4 Control section 14 The control unit 14 may include a processor such as a central processing unit (CPU), a digital signal processor, a microprocessor, a microcontroller, an application specific integrated circuit (ASIC), a programmable logic device (PLD), or the like.

[0022] The control unit 14 includes a power transmission control unit 14a and a frequency adjustment unit 14b as functional components. The power transmission control unit 14a can control the power transmission unit 11 based on information received from the communication unit 13. For example, the power transmission control unit 14a can be configured to be controllable to start or stop power transmission based on distance information between the power transmission coil 11a and the receiving coil.

[0023] The frequency adjuster 14b can be configured to adjust the resonant frequency f2 of the relay coil unit 12 based on the information received from the communication unit 13. Specifically, the frequency adjuster 14b can be configured to be able to adjust a variable capacitor connected to the relay coil 12a included in the relay coil unit 12 based on the distance information.

[0024] 1.2 Power receiving device 20 The power receiving device 20 includes a power receiving coil 21, a power storage loop coil 22, a rectifier circuit 23, and a storage battery 24. The power receiving coil 21 can receive power transmitted from the power transmitting coil 11a using electromagnetic force such as magnetic resonance. The power received by the power receiving coil 21 is taken out from the power storage loop coil 22 via the rectifier circuit 23 and stored in the storage battery 24.

[0025] The power receiving device 20 may be any device capable of being charged contactlessly via the power receiving coil 21, such as an electric vehicle, an in-body medical device, or a home appliance.

[0026] Furthermore, the power receiving device 20 is movable with respect to the power transmitting device 10. For example, every time a user parks an electric vehicle (power receiving device 20) with respect to a charging station where the power transmitting device 10 is installed, the positional relationship between the power transmitting coil 11a and the power receiving coil 21 changes. Therefore, the positional relationship between the power receiving coil 21 and the power transmitting coil 11a can change.

[0027] 1.3 Sensor device 30 The sensor device 30 includes a sensor unit 31 and a communication unit 32. The sensor unit 31 can be any sensor as long as it can measure the position of the power receiving coil 21 relative to the power transmitting coil 11a (hereinafter, position information) and the distance between the power transmitting coil 11a and the power receiving coil 21 (hereinafter, distance information). The communication unit 32 is configured to be able to communicate the position information and distance information measured by the sensor unit 31 with the communication unit 13 of the power transmitting device 10.

[0028] 1.5. Characteristics of relay coil 12a Here, the characteristics of the relay coil 12a will be described using a configuration in which the power transmitting coil 11a, the relay coil unit 12 including one relay coil 12a, and the power receiving coil 21 are arranged coaxially in this order (FIG. 2). More specific characteristics of the relay coil 12a will be described in an embodiment described later, but the relay coil 12a arranged between the power transmitting coil 11a and the power receiving coil 21 has a property that the direction of the magnetic field changes with a change in the resonant frequency f2 of the relay coil 12a, with the resonant frequency f1 of the power transmitting and receiving coils as a boundary.

[0029] 4 and 5 are examples showing the magnetic field distribution generated around each coil in the WPT system 100 by simulation, and the arrows indicate the direction of the magnetic field. In Fig. 4 and Fig. 5, the resonant frequency f1 of the power transmitting and receiving coils is 13.56 MHz, and the resonant frequency f2 of the relay coil 12a is 15 MHz in Fig. 4 and 12 MHz in Fig. 5.

[0030] As shown in Fig. 4, when the resonant frequency f2 of the relay coil 12a shifts to the higher frequency side from the resonant frequency f1 of the power transmitting and receiving coils, the relay coil 12a has the characteristic of acting as a relay without changing the direction of the magnetic field generated between the power transmitting and receiving coils. On the other hand, as shown in Fig. 5, when the resonant frequency f2 of the relay coil 12a shifts to the lower frequency side, the direction of the magnetic field is reversed, and the relay coil 12a has the characteristic of acting as an obstruction.

[0031] Furthermore, the greater the difference between the resonant frequency f2 of the relay coil 12a and the resonant frequency f1 of the power transmitting and receiving coils, the less the effect that the relay coil 12a has on the magnetic field generated between the power transmitting and receiving coils.

[0032] That is, the coupling coefficient between the power transmitting coil 11a and the power receiving coil 21 changes depending on the resonant frequency f2 of the relay coil 12a. Therefore, by adjusting the resonant frequency f2 of the relay coil 12a, it is possible to adjust the coupling coefficient between the power transmitting coil 11a and the power receiving coil 21. The WPT system 100 is configured to be able to keep the coupling coefficient between the power transmitting coil 11a and the power receiving coil 21 constant regardless of the distance between the power transmitting coil 11a and the power receiving coil 21 by utilizing the characteristics due to the resonant frequency f2 of the relay coil 12a.

[0033] The resonance frequency f2 of the relay coil 12a can be calculated by the following formula.

number

[0034] 1.5.2 Frequency Regulation As described above, the frequency adjuster 14b adjusts the capacitance of the capacitor of the relay coil 12a of the relay coil unit 12, and adjusts the resonant frequency f2, based on various information from the sensor device 30. Here, adjustment of the resonant frequency f2 of the relay coil 12a will be described for the case where the position of the power receiving coil 21 is shifted in the radial direction of the coil from the arrangement in which the position of the power receiving coil 21 is coaxial with the power transmitting coil 11a, that is, from the case where the deviation X between the central positions of the power transmitting coil 11a and the power receiving coil 21 is 0 cm.

[0035] The relay coil unit 12 according to this embodiment is disposed horizontally with the power transmitting coil 11a and between the power transmitting coil 11a and the power receiving coil 21, so that the resonant frequency f2 of the relay coil 12a is adjusted to a range higher than the resonant frequency f1 of the power transmitting and receiving coils so as to relay the magnetic field generated around the power transmitting coil 11a as is. Also, in order to prevent the power transmitting coil 11a and the power receiving coil 21 from coupling with the relay coil 12a, the resonant frequency f2 of the relay coil 12a is different from the resonant frequency f1 of the power transmitting and receiving coils.

[0036] When the offset X between the power transmitting coil 11a and the power receiving coil 21 is 0 cm, the distance between the power transmitting coil 11a and the power receiving coil 21 is relatively close compared to other positional relationships, and the coupling coefficient between the power transmitting and receiving coils is approximately maximum. Therefore, in this arrangement, power can be transferred relatively efficiently, and the resonant frequency f2 of the relay coil 12a is adjusted by the frequency adjustment unit 14b to a value significantly different from the resonant frequency f1 of the power transmitting and receiving coils so as not to affect the magnetic field between the power transmitting coil 11a and the power receiving coil 21.

[0037] For example, when the resonant frequency f1 of the power transmitting and receiving coils is 13.56 MHz, the resonant frequency f2 of the relay coil 12a can be adjusted to be 20 MHz or higher.

[0038] As the difference X increases, the coupling coefficient between the power transmitting coil 11a and the power receiving coil 21 decreases. The frequency adjusting unit 14b adjusts the resonance frequency f2 to decrease from the resonance frequency f2 of the relay coil 12a at 0 cm to approach the resonance frequency f1 of the power transmitting and receiving coils as the difference X increases. As described above, the closer the resonance frequency f2 of the relay coil 12a is to the resonance frequency f1 of the power transmitting coil 11a, the greater the effect it has on the magnetic field. Therefore, by adjusting the resonance frequency f2 of the relay coil 12a to approach the resonance frequency f1 of the power transmitting coil 11a as the difference X increases, it is possible to compensate for the decrease in the coupling coefficient due to the difference X.

[0039] In the WPT system 100, the power receiving device 20 can compensate for the decrease in coupling coefficient and maintain transmission efficiency if the power receiving coil 21 provided in the power receiving device 20 is shifted by X to a position where it at least partially overlaps with the power transmitting coil 11a or the relay coil 12a in the axial direction.

[0040] In addition, in conventional WPT using a repeater coil, it was necessary to design the resonant frequency of the power transmitting and receiving coils to be the same as that of the repeater coil, so all coils had to be designed as a single unit, which made the design complicated. In the WPT system 100, the resonant frequency f2 of the relay coil 12a has a different value from the resonant frequency f1 of the power transmitting and receiving coils, so it is only necessary to consider the coupling coefficient between the power transmitting and receiving coils, making the design easy.

[0041] 2. Second embodiment The WPT system 100 according to this embodiment differs from the first embodiment in that the relay coil unit 12 includes a first relay coil 12a and a second relay coil 12b. The following description will focus on the differences from the first embodiment.

[0042] 6 is a schematic diagram showing a WPT system 100 according to this embodiment. The relay coil unit 12 included in the power transmission device 10 according to this embodiment includes a first relay coil 12a and a second relay coil 12b on the same plane. The inner diameter of the second relay coil 12b is larger than the outer diameter of the first relay coil 12a, and the second relay coil 12b is concentrically arranged outside the first relay coil 12a.

[0043] The larger the diameter of the relay coil, the larger the coupling coefficient between the transmitting and receiving coils. However, as shown in the above formula, the resonant frequency f2 depends on the inductance and capacitance of the coil, so in order to maintain the resonant frequency f2 within a certain range, the inductance cannot be made larger than necessary. In other words, there is a limit to increasing the number of turns and the diameter of the coil.

[0044] In this embodiment, by arranging the first relay coil 12a and the second relay coil 12b in a double configuration, it is possible to configure a relay coil unit 12 having a large diameter by combining the first and second relay coils 12b while maintaining a predetermined range of resonant frequency. Therefore, it is possible to further strengthen the coupling coefficient between the power transmitting and receiving coils. The resonant frequency f2 of the first relay coil 12a and the second relay coil 12b is configured to be adjustable by the frequency adjustment unit 14b.

[0045] Furthermore, the relay coil unit 12 may include a plurality of relay coils arranged concentrically with the third relay coil, the fourth relay coil, etc., outside the second relay coil 12b. The relay coil unit 12 may include a plurality of relay coils arranged concentrically, similar to an arrangement shown in Fig. 3, so that they at least partially overlap in the axial direction and are arranged horizontally with the power transmission coil 11a.

[0046] 3. Third embodiment The WPT system 100 according to this embodiment differs from the first embodiment in that the relay coil unit 12 includes a relay coil 12a arranged on the same plane as the power transmission coil 11a. The following description will focus on the differences from the first embodiment.

[0047] 7 is a schematic diagram showing a WPT system 100 according to this embodiment. The relay coil unit 12 according to this embodiment includes a relay coil 12a on the same plane as the power transmitting coil 11a. The inner diameter of the relay coil 12a is larger than the outer diameter of the power transmitting coil 11a, and the relay coil 12a is concentrically arranged outside the power transmitting coil 11a. Similar to this arrangement, a relay coil 12b may be further arranged outside the power receiving coil 21. Furthermore, a plurality of relay coils may be further arranged concentrically outside the relay coil 12a arranged outside the power transmitting coil 11a and / or the power receiving coil 21.

[0048] By arranging the relay coils 12a and 12b concentrically with the power transmitting coil 11a and / or the power receiving coil 21, the diameters of the power transmitting coil 11a and the power receiving coil 21 can be increased in an artificial manner by the combination of the power transmitting coil 11a and the relay coil 12a and the combination of the power receiving coil 21 and the relay coil 12b. Therefore, the coupling coefficient between the power transmitting coil 11a and the power receiving coil 21 can be further strengthened.

[0049] The relay coil unit 12 of this embodiment may further include a relay coil arranged between the transmitting coil 11a and the receiving coil 21, as shown in the first or second embodiment, in addition to the relay coils 12a, 12b arranged outside the transmitting coil 11a and / or the receiving coil 21.

[0050] 4. Fourth embodiment The WPT system 100 according to this embodiment differs from the first embodiment in that the relay coil unit 12 includes a plurality of relay coils on the same plane. The following description will focus on the differences from the first embodiment.

[0051] Fig. 8 is a schematic diagram showing a WPT system 100 according to this embodiment. Fig. 8 shows, as an example, a configuration including a relay coil unit 12 including eight relay coils 12a to 12h. In the relay coil unit 12 according to this embodiment, the center positions between the relay coils 12a to 12h are arranged coaxially with the center position of the power transmission coil 11a. Moreover, each of the relay coils 12a to 12h is preferably arranged horizontally with the power transmission coil 11a so as to overlap at least a portion of the relay coil 12a to 12h in the axial direction.

[0052] In the relay coil unit 12 according to this embodiment, a plurality of relay coils are arranged on the same plane, so that the range in which the transmission efficiency can be kept constant with respect to the positional deviation X of the power receiving coil 21 is widened.

[0053] The resonant frequency f2 of the relay coil unit 12 is configured to be adjustable for each relay coil included in the relay coil unit 12. For example, based on position information measured by the sensor device 30, the frequency adjuster 14b can adjust only the resonant frequency f2 of the relay coil that is closest to the position where the power receiving coil 21 is located.

[0054] 5. Fifth embodiment The WPT system 100 according to this embodiment differs from the first embodiment in that the relay coil unit 12 is arranged so as to face the direction of the magnetic field generated from the power transmitting coil to the power receiving coil with respect to the power transmitting coil 11a and outside the width of the power transmitting coil 11a. Note that the following mainly describes the differences from the first embodiment.

[0055] Fig. 9 is a schematic diagram showing the WPT system 100 according to this embodiment as viewed from above. Fig. 9 shows a configuration including a relay coil unit 12 having relay coils 12a and 12b arranged perpendicular to the power transmission coil 11a and outside the width of the power transmission coil 11a, one each in the front-rear direction, but the relay coils may be arranged only in one direction in the front-rear direction, or three or more may be arranged.

[0056] Furthermore, the orientation of the relay coils 12a and 12b does not need to be perpendicular to the power transmission coil 11a, and can be arbitrarily arranged as long as leakage of the magnetic field can be suppressed by adjusting the resonant frequency of the relay coil unit 12 described below.

[0057] Furthermore, the relay coil unit 12 according to this embodiment differs from the first to fourth embodiments in the adjustable range of the resonant frequency of the relay coil unit 12.

[0058] As described above, the relay coil has a property of changing the direction of the magnetic field at the boundary of the resonant frequency f1 of the power transmitting and receiving coils in accordance with the resonant frequency f2. The relay coil unit 12 according to this embodiment is adjusted by the frequency adjustment unit 14b to a value smaller than the resonant frequency f1 of the power transmitting and receiving coils. Due to this adjustment range, the magnetic field that was previously a leakage magnetic field and faces outward is changed to the opposite direction by the relay coil unit 12 with a low resonant frequency arranged outside the power transmitting coil 11a, thereby relaying the transmitted power to the power receiving coil 21.

[0059] That is, the relay coil unit 12 according to this embodiment can suppress leakage of the magnetic field by utilizing the property of reversing the direction of the magnetic field when the frequency shifts to the lower frequency side than the resonant frequency f1 of the power transmitting and receiving coils.

[0060] The relay coil unit 12 according to this embodiment may further include the relay coil arrangement described in the first to fourth embodiments. In the example of Fig. 10, the transmission distance can be extended by a plurality of relay coils arranged horizontally with the power transmitting coil 11a, and the leakage of the magnetic field can be suppressed by a coil arranged perpendicular to the power transmitting coil 11a.

[0061] 6. Other embodiments 6.1 WPT System 100 In the above-described WPT system 100, the sensor device 30 is configured separately from the power transmitting device 10. However, the power transmitting device 10 may be configured to have the function of the sensor device 30.

[0062] 6.2 Transmitting and receiving coil arrangement In the WPT system 100, the power transmitting coil 11a and the power receiving coil 21 may be concentrically arranged on the same plane. In this case, it is preferable that the relay coil unit 12 is arranged between the power transmitting coil 11a and the power receiving coil 21 on the same plane.

[0063] 6.3 Relay coil unit configuration In the WPT system 100, the relay coil unit 12 can include a relay coil 12a on the same plane as the power transmitting coil 11a. In this embodiment, the inner diameter of the power transmitting coil 11a is larger than the outer diameter of the relay coil 12a, and the power transmitting coil 11a may be arranged concentrically outside the relay coil 12a. In this case, a relay coil 12b may be further arranged inside the power receiving coil 21 in the same manner as the above arrangement.

[0064] 7. Working Example The effect that the relay coil unit 12 of the WPT system 100 has on the coupling coefficient or transmission efficiency will be described below with specific experimental results.

[0065] 7.1 Characteristics of relay coil 12a due to resonant frequency 7.1.1 Experimental overview The changes in the transmission efficiency and coupling coefficient when the resonant frequency f2 of the relay coil 12a is changed were clarified by simulation and measurement for two layout configurations. The usefulness of the relay coil 12a was demonstrated by comparing the transmission efficiency with that when the relay coil 12a is not used.

[0066] 7.1.2 Coil used Three coils were used: a power transmission coil 11a, a power receiving coil 21, and a relay coil 12a. Each coil was made of copper wire with a wire width of 12 mm and a thickness of 0.1 mm, and the support material was polystyrene foam, which has low dielectric loss and allows the wire to be embedded. The size of the support material was 30 cm wide x 33 cm long x 3 cm thick.

[0067] The resonant frequency f1 of the power transmitting coil 11a was set to 13.56 MHz. The number of turns of the relay coil 12a was reduced compared to the power transmitting and receiving coils, and the resonant frequency was set higher in advance. A socket was attached to the universal board to connect a variable capacitor to the relay coil 12a.

[0068] 7.1.3 Arrangement of relay coil 12a This experiment was performed with two measurement arrangements. Fig. 11 is a diagram showing the first measurement arrangement, in which relay coil 12a is arranged horizontally with power transmitting coil 11a and power receiving coil 21 (hereinafter referred to as horizontal arrangement). Fig. 12 is a diagram showing the second measurement arrangement, in which relay coils 12a and 12b are arranged vertically with power transmitting coil 11a and power receiving coil 21 (hereinafter referred to as vertical arrangement). In the vertical arrangement, the distance D2 from the center to relay coils 12a and 12b was set to 15 cm, and the resonant frequencies f2 of the two relay coils 12a and 12b were adjusted to be the same.

[0069] 7.1.2 Experimental method The simulation was performed using a three-dimensional electromagnetic field simulator CST MW Studio. First, a simulation of WPT without a relay coil was performed with the distance D1 between the transmitting and receiving coils set to 40 cm, and the coupling coefficient and transmission efficiency were derived. Then, simulations were performed with horizontal and vertical arrangements. The distance D1 between the transmitting and receiving coils was set to 40 cm, the same as when the relay coil 12a (12b) was not used, and in the horizontal arrangement, the relay coil 12a was placed at the middle position between the transmitting coil 11a and the receiving coil 21 so that the center of the relay coil 12a was located coaxially with the center of the transmitting and receiving coils. The transmission efficiency and coupling coefficient were calculated when the resonant frequency f2 of the relay coil 12a (12b) was changed in increments of 0.5 MHz from 10 to 17 MHz. Measurements were also performed using actual coils under the same conditions as the simulation.

[0070] 7.1.3 Results (1)Horizontal arrangement The transmission efficiency when the resonant frequency f2 of the relay coil 12a is changed is shown in Fig. 13, and the coupling coefficient is shown in Fig. 14. In the horizontal arrangement, by using a relay coil 12a with a lower frequency than the resonant frequency f1 of the power transmitting and receiving coils, the transmission efficiency decreased compared to when the relay coil 12a was not used, and by using a high-frequency relay coil 12a, the transmission efficiency improved. It was found that the closer the resonant frequency f2 of the relay coil 12a is to the resonant frequency f1 of the power transmitting and receiving coils, the greater the effect on the WPT, and the further away it is, the smaller the effect becomes, approaching the transmission efficiency of WPT without using the relay coil 12a.

[0071] It was also found that the coupling coefficient between the power transmitting and receiving coils changes when the resonant frequency f2 of the relay coil 12a changes. Therefore, it was found that by setting the resonant frequency f2 of the relay coil 12a to a high frequency, the coupling coefficient between the power transmitting and receiving coils increases, and the transmission efficiency improves accordingly.

[0072] (2)Vertical arrangement The transmission efficiency when the resonant frequency f2 of the relay coils 12a and 12b is changed is shown in Fig. 15, and the coupling coefficient is shown in Fig. 16. In the vertical arrangement, by using relay coils 12a and 12b with a lower frequency than the resonant frequency f1 of the power transmitting and receiving coils, the transmission efficiency was improved compared to the case where the relay coils 12a and 12b were not used. On the other hand, when high-frequency relay coils 12a and 12b were used, the transmission efficiency decreased. This is the opposite result to the horizontal arrangement, and it became clear that it is necessary to use different resonant frequencies f2 of the relay coils 12a and 12b depending on the location where the relay coils 12a and 12b are arranged.

[0073] Furthermore, even in this arrangement, it was found that the closer the resonant frequency f2 of the relay coils 12a and 12b is to the resonant frequency f1 of the transmitting and receiving relay coil, the greater the effect on the WPT, and the farther away it is, the smaller the effect becomes, approaching the transmission efficiency of the WPT that does not use the relay coils 12a and 12b.

[0074] 7.2 Change in transmission efficiency depending on the axial distance between the transmitting and receiving coils 7.2.1 Experimental overview When the distance D1 between the transmitting and receiving coils increases, the coupling coefficient decreases, and the transmission efficiency decreases. Therefore, by using two measurement arrangements, we clarified to what extent the transmission efficiency can be improved by the relay coil 12a (12b) when the distance D1 between the transmitting and receiving coils is increased.

[0075] 7.2.2 Experimental method The coil parameters, simulator, etc. were the same as those in the above experiment. In this experiment, the distance D1 between the transmitting and receiving coils was changed from 40 cm to 5 cm each time, and simulations and measurements were performed without and with the relay coil 12a (12b), and the transmission efficiency was calculated. The resonance frequency f2 of the relay coil 12a (12b) was fixed at 15 MHz in the horizontal arrangement and 12 MHz in the vertical arrangement, and the relay coil 12a (12b) was arranged so that it was located in the middle each time depending on the coil distance D1 between the transmitting and receiving coils.

[0076] Furthermore, in the vertical arrangement, the distance D2 from the center to the relay coils 12a and 12b was set to 2 cm, and simulations and measurements were performed with and without the relay coils 12a and 12b, and the transmission efficiency was calculated.

[0077] 7.2.3 Results (1)Horizontal arrangement Fig. 17 shows the transmission efficiency when the distance D1 between the transmitting and receiving coils is changed. As the distance D1 between the transmitting and receiving coils increases, the transmission efficiency decreases significantly, but by providing the relay coil 12a, the transmission efficiency is improved compared to when the relay coil 12a is not used.

[0078] (2)Vertical arrangement Fig. 18 shows the transmission efficiency when the distance D1 between the transmitting and receiving coils is changed. When relay coils 12a and 12b are not used, the transmission efficiency decreases significantly as the distance D1 between the transmitting and receiving coils increases, but by providing relay coils 12a and 12b, the transmission efficiency is improved compared to when relay coils 12a and 12b are not used.

[0079] Moreover, Fig. 19 shows the transmission efficiency when the relay coil distance D2 is changed. The transmission efficiency hardly changes even when the relay coil distance D2 is increased. Therefore, even if the positions of the relay coils 12a and 12b are slightly misaligned, the coupling coefficient between the transmitting and receiving coils hardly changes, so it is not necessary to design the transmitting and receiving coils and the repeater coil as one unit as in the conventional technology, and it was found that the WPT can be easily designed.

[0080] 7.3 Change in transmission efficiency due to misalignment of the transmitting and receiving coils 7.3.1 Experiment overview When the radial position of the transmitting and receiving coils is misaligned, the coupling coefficient decreases, resulting in a decrease in transmission efficiency. Therefore, we clarified whether the transmission efficiency can be kept constant by adjusting the resonance frequency f2 of the relay coil 12a even when the misalignment X of the transmitting and receiving coils is increased.

[0081] 7.3.2 Experimental method A schematic diagram of this experiment is shown in Fig. 20. The coil parameters, simulator, etc. used were the same as those used in the above experiment. In this experiment, the offset X of the center position of the power transmitting and receiving coils was shifted from 0 cm to 10 cm at a time, and simulations were performed with and without the relay coil 12a, and the transmission efficiency and coupling coefficient were calculated. The resonant frequency of the relay coil 12a was adjusted between 14 and 19 MHz, and the position of the relay coil 12a was fixed.

[0082] 7.3.3 Results FIG. 21 shows the transmission efficiency when the positions of the transmitting and receiving coils are shifted, and FIG. 22 shows the coupling coefficient. As shown in FIG. 21, when the relay coil 12a is not used, when the position of the receiving coil 21 is shifted, the transmission efficiency significantly decreases as the shift X increases. This is because the coupling coefficient between the transmitting and receiving coils decreases as shown in FIG. 22. Therefore, if the resonant frequency f2 of the relay coil is investigated so that the coupling coefficient between the transmitting and receiving coils for each shift X approaches the coupling coefficient (0.018) when the shift X is 0 cm when the relay coil 12a is inserted, the coupling coefficient between the transmitting and receiving coils can be kept constant for any shift X simply by adjusting the resonant frequency f2 of the relay coil (FIG. 22), and the transmission efficiency between the transmitting and receiving coils can be kept at the transmission efficiency when it is 0 cm (FIG. 21). In this case, by fabricating a capacitor bank and configuring it so that a desired capacitance can be obtained by switching, the transmission efficiency can be instantly kept constant for any X by switch control. [Explanation of symbols]

[0083] 10: Power transmission equipment 11: Power transmission section 11a: Transmitting coil 11b: Power supply loop coil 11c: Power supply 12: Relay coil unit 12a~12h: Relay coil 13: Communications Department 14: Control section 14a: Power transmission control unit 14b: Frequency adjustment section 20: Power receiving device 21: Receiving coil 22: Loop coil for storing electricity 23: Rectifier circuit 24: Battery 30: Sensor device 31: Sensor section 32: Communications Department 100: WPT system D1: Distance between the transmitting and receiving coils D2: Distance between relay coils

Claims

1. A wireless power transmission system, The power transmission device includes a power receiving coil, a relay coil unit, and a frequency adjusting unit. The power transmitting coil transmits power to the power receiving coil by using electromagnetic force, the relay coil unit relays power transmission from the power transmitting coil to the power receiving coil, The frequency adjustment unit is configured to adjust a resonant frequency of the relay coil unit in accordance with a distance between the power transmitting coil and the power receiving coil.

2. 2. The wireless power transmission system according to claim 1, A wireless power transmission system, wherein the frequency adjustment unit is configured to adjust a resonant frequency of the relay coil unit by changing a capacitance of a capacitor connected to a relay coil provided in the relay coil unit.

3. 2. The wireless power transmission system according to claim 1, The relay coil unit is arranged horizontally with respect to the power transmission coil and at least partially overlaps with the power transmission coil in the axial direction.

4. 2. The wireless power transmission system according to claim 1, the relay coil unit includes first and second relay coils arranged on the same plane; A wireless power transmission system, wherein the inner diameter of the second relay coil is larger than the outer diameter of the first relay coil and is disposed outside the first relay coil.

5. 2. The wireless power transmission system according to claim 1, the relay coil unit includes a relay coil that is disposed on the same plane as the power transmission coil, A wireless power transmission system, wherein an inner diameter of the relay coil is larger than an outer diameter of the power transmission coil and the relay coil is disposed outside the power transmission coil.

6. 2. The wireless power transmission system according to claim 1, A wireless power transmission system, wherein the relay coil unit includes a plurality of relay coils, each of which is arranged on the same plane.

7. 2. The wireless power transmission system according to claim 1, A wireless power transmission system, wherein the relay coil unit is arranged so as to face the direction of a magnetic field generated from the power transmitting coil to the power receiving coil and outside the width of the power transmitting coil.

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