Wireless power transmission system, power transmitting device, power receiving device, and mobile object

Abstract

To provide a wireless power transmission system, a power transmission device, a power reception device, and a mobile body, capable of performing stable power transmission using electric field coupling.SOLUTION: A wireless power transmission system 1 comprises a power transmission device 10 and a power reception device 20 and transmits power wirelessly using electric field coupling. The power transmission device 10 comprises a pair of power transmission electrode units 12 that have power transmission side feeding points 12a at one ends and outputs power supplied from the power transmission side feeding points 12a, the power generated by a high frequency generation unit 11. The power reception device 20 comprises a pair of power reception electrode units 21 that have power reception side feeding points 21a at one ends on the other sides of the power transmission electrode units 12 when facing the transmission electrode units 12, receives power output from the power transmission electrode units 12 using electric field coupling, and feeds power to a battery 31 from the power reception side feeding points 21a. Each of the power transmission electrode units 12 and the power reception electrode units 21 has a length (L1+L2+L3) of a transmission line that is 1 / 4 of a wavelength of power to be transmitted, in the case of performing equivalent conversion of the electrode unit to the transmission line.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a wireless power transmission system that transmits power wirelessly by electric field coupling, a power transmitting device and a power receiving device used in the wireless power transmission system, and a mobile object equipped with the power receiving device. [Background technology]

[0002] In recent years, electric vehicles and unmanned, autonomous electric vehicles have attracted attention, and various research and development efforts have been conducted. To popularize these electric vehicles and electric vehicles, issues such as the cost and weight of the batteries they are equipped with, the length of their power supply time, the difficulty of recycling, and increased labor costs have become problems. Unmanned, contactless power supply technology is being considered as one method for solving these issues.

[0003] Such contactless power supply methods include, for example, electric field coupling and magnetic coupling. The electric field coupling method transmits power contactlessly by transmitting power through space as electric field energy using a capacitor formed between the power transmitting electrode and the power receiving electrode (for example, Patent Document 1 and Non-Patent Document 1). This electric field coupling method does not require the installation of expensive coils as in the magnetic coupling method, so it can be implemented at low cost and is suitable for contactless power supply that requires power transmission equipment over a wide area. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-184824 [Non-patent literature]

[0005] [Non-Patent Document 1] Y. Naka, M. Tamura, “Representation of an equivalent circuit for capacitive wireless power transfer using a distributed-constant circuit,” IEICE Communication Express, Institute of Electronics, Information and Communication Engineers, October 2020, Vol. 9, No. 10, pp. 457-463 Summary of the Invention [Problem to be solved by the invention]

[0006] In the electric field coupling method, the coupling coefficient in the electric field coupling varies due to variations in the transmission distance and relative position between the power transmitting electrode and the power receiving electrode. Furthermore, when the transmitted power is charged to a battery, the load resistance of the battery varies depending on the charging state. These variations cause fluctuations in the input impedance or admittance seen from the high-frequency inverter, resulting in impedance mismatch, increased reflected power, and reduced power transmission efficiency. Furthermore, variations in the imaginary part of the input impedance seen from the high-frequency inverter prevent the high-frequency inverter from performing ideal operations such as ZVS (Zero Volt Switching), potentially resulting in thermal damage to switching elements and other elements. Patent Document 1 discloses a wireless power supply device that can reduce the decrease in efficiency due to variations in load resistance, but does not address the above-mentioned problem of variations in the coupling coefficient.

[0007] The present invention has been made to solve the above problems, and aims to provide a wireless power transmission system, a power transmitting device, a power receiving device, and a mobile object that are capable of stable power transmission through electric field coupling. [Means for solving the problem]

[0008] To achieve this object, a wireless power transmission system according to claim 1 includes a power transmitting device and a power receiving device provided on a mobile body that can move relative to the power transmitting device, and transmits power wirelessly from the power transmitting device to the power receiving device by electric field coupling. The power transmitting device includes a high frequency generating unit that generates high frequency power, and a flat-plate-shaped power transmitting device having a power transmitting side feeding point at one end and an open end at the other end. And rectangular and a pair of power transmission electrode units configured with a conductor of the same type as the power receiving electrode unit, and outputting power generated by the high frequency generating unit and fed from the power transmission side feeding point, wherein the power receiving device is a flat plate-like device provided in a position that allows it to face the power transmission electrode units, has a power receiving side feeding point at one end that is located on the other end side of the power transmission electrode unit when it faces the power transmission electrode unit, and has the other end in an open state. And rectangular and a power receiving electrode unit configured with a conductor of a power transmitting electrode unit, which receives the power output from the power transmitting electrode unit by electric field coupling and supplies the power received from the power receiving side feed point to a load provided on the mobile body, wherein when the power transmitting electrode unit and the power receiving electrode unit are equivalently converted into transmission lines, the lengths of the transmission lines are ¼ of the wavelength of the power to be transmitted. Here, the length of the transmission line only needs to be substantially ¼ of the wavelength of the power to be transmitted, and only needs to be a length that generates a phase difference of substantially π / 2 in the transmission line.

[0009] The wireless power transmission system according to claim 2 includes a power transmitting device and a power receiving device provided on a mobile body movable relative to the power transmitting device, and transmits power wirelessly from the power transmitting device to the power receiving device by electric field coupling, wherein the power transmitting device includes a high-frequency generating unit that generates high-frequency power, a pair of power transmitting electrodes configured by a flat conductor having a power transmitting side feeding point at one end and an open end at the other end, and outputting the power generated by the high-frequency generating unit fed from the power transmitting side feeding point, and a power transmitting side inductor connected in series between the high-frequency generating unit and the power transmitting electrode units, and the power receiving device is provided in a pair at positions that can face the power transmitting electrode units, a power receiving electrode unit configured of a flat conductor having a power receiving-side feed point at one end that is located on the other end side of the power transmitting electrode unit when facing the power transmitting electrode unit, and the other end being in an open state, receiving power output from the power transmitting electrode unit by electric field coupling and feeding the power received from the power receiving-side feed point to a load provided on the mobile body; and a power receiving-side inductor connected in series between the power receiving electrode unit and the load, wherein the inductances of the power transmitting-side inductor and the power receiving-side inductor are adjusted so that a reflection coefficient of power seen from the high-frequency generation unit changes on the real axis of a Smith chart with respect to a variation in a coupling coefficient of the electric field coupling formed by the power transmitting electrode unit and the power receiving electrode unit. The power transmitting inductor and the power receiving inductor are designed in advance and have the designed inductance. Here, the change in the power reflection coefficient seen from the high frequency generating unit on the real axis of the Smith chart in response to a change in the coupling coefficient of the electric field coupling formed by the power transmitting electrode unit and the power receiving electrode unit means that the change in the power reflection coefficient seen from the high frequency generating unit on the real axis of the Smith chart is sufficient as long as it can be said that the change is substantially on the real axis of the Smith chart, and it is not necessary that the change is absolutely on the real axis of the Smith chart. design In these cases, it is not necessary to use a Smith chart. design As a result, it is sufficient that the reflection coefficient varies on the real axis of the Smith chart in response to the variation of the coupling coefficient.

[0010] The wireless power transmission system according to claim 3 includes a power transmitting device and a power receiving device provided on a mobile body movable relative to the power transmitting device, and transmits power wirelessly from the power transmitting device to the power receiving device by electric field coupling, wherein the power transmitting device includes a high-frequency generating unit that generates high-frequency power, a pair of power transmitting electrodes configured by a flat conductor having a power transmitting-side feeding point at one end and an open end at the other end, and outputting the power generated by the high-frequency generating unit that is fed from the power transmitting-side feeding point, and a power transmitting-side inductor connected in series between the high-frequency generating unit and the power transmitting electrode units, and the power receiving device is provided in a pair at a position that can face the power transmitting electrode units, and when facing the power transmitting electrode units, a power receiving electrode unit configured by a flat conductor having a power receiving-side feed point at one end thereof on the other end side of the power transmitting electrode unit and the other end in an open state, the power receiving electrode unit receiving power output from the power transmitting electrode unit by electric field coupling and feeding the power received from the power receiving-side feed point to a load provided on the mobile body; and a power receiving-side inductor connected in series between the power receiving electrode unit and the load, wherein the inductances of the power transmitting-side inductor and the power receiving-side inductor and the length of the transmission line between the high frequency generating unit and the power transmitting electrode unit are adjusted so that a reflection coefficient of power as seen from the high frequency generating unit changes on the real axis of a Smith chart with respect to a variation in a coupling coefficient of the electric field coupling formed by the power transmitting electrode unit and the power receiving electrode unit. The power transmitting side inductor and the power receiving side inductor are designed in advance and have the designed inductances, and a transmission line is provided between the high frequency generating unit and the power transmitting electrode unit so as to have the designed transmission line length. Here, the change in the power reflection coefficient seen from the high frequency generating unit on the real axis of the Smith chart in response to a change in the coupling coefficient of the electric field coupling formed by the power transmitting electrode unit and the power receiving electrode unit means that the change in the power reflection coefficient seen from the high frequency generating unit is sufficient to be considered to be substantially on the real axis of the Smith chart, and does not necessarily have to be on the real axis of the Smith chart. design In these cases, it is not necessary to use a Smith chart. design As a result, it is sufficient that the reflection coefficient varies on the real axis of the Smith chart in response to the variation of the coupling coefficient.

[0011] The power transmitting device according to claim 4 is used in the wireless power transmission system according to any one of claims 1 to 3.

[0012] A power receiving device according to a fifth aspect of the present invention is used in the wireless power transmission system according to any one of the first to third aspects of the present invention.

[0013] A moving object according to a sixth aspect of the present invention includes the power receiving device according to the fifth aspect of the present invention. [Effects of the Invention]

[0014] According to the wireless power transmission system of claim 1, in the power transmitting device, high-frequency power generated by a high-frequency generating unit is output from a pair of power transmitting electrodes. The power output from the power transmitting electrodes is received wirelessly by the power receiving electrodes through electric field coupling when a pair of power receiving electrodes of a power receiving device provided on a mobile object are positioned opposite the power transmitting electrodes. The received power is supplied to a load provided on the mobile object. Here, the power transmitting side power supply point, where the power generated by the high-frequency generating unit is supplied to the power transmitting electrodes, is a flat-plate-shaped And rectangular The power receiving electrode is provided at one end of the power transmitting electrode section, which is made of a conductor, and the other end is open. And rectangular The receiving-side feed point of the power receiving electrode, which is composed of a conductor, is located at one end that is opposite the power transmitting electrode when facing the power transmitting electrode, and the other end is open. In addition, when the power transmitting electrode and the power receiving electrode are each converted into an equivalent transmission line, the length of the transmission line is 1 / 4 of the wavelength of the transmitted power. As a result, the electric field coupler formed by the power transmitting electrode and the power receiving electrode becomes a λ / 4 inverted coupler and can be converted into an equivalent gyrator. Therefore, even if the actual resistance of the load connected to the power receiving electrode fluctuates or the coupling coefficient fluctuates due to changes in the spacing or relative positions between the power transmitting electrode and the power receiving electrode, the λ / 4 inverted coupler functions as a gyrator, thereby enabling stable power transmission by electric field coupling without using a matching circuit for impedance matching.

[0015] According to the wireless power transmission system of claim 2, in a power transmitting device, high-frequency power generated by a high-frequency generating unit is output from a pair of power transmitting electrodes. The power output from the power transmitting electrodes is wirelessly received by the power receiving electrodes through electric field coupling when a pair of power receiving electrodes of a power receiving device provided in a mobile object are positioned opposite the power transmitting electrodes. The received power is supplied to a load provided in the mobile object. Here, a power transmitting-side feeding point through which the power generated by the high-frequency generating unit is supplied to the power transmitting electrodes is provided at one end of the power transmitting electrodes formed by a flat conductor, and the other end is open. Meanwhile, a power receiving-side feeding point of the power receiving electrode formed by a flat conductor, which supplies the received power to the load, is provided at one end on the other side of the power transmitting electrodes when facing the power transmitting electrodes, and the other end is open. In addition, the inductance of the power transmitting side inductor connected in series between the high frequency generating unit and the power transmitting electrode unit, and the inductance of the power receiving side inductor connected in series between the power receiving electrode unit and the load are set so that the reflection coefficient of the power seen from the high frequency generating unit changes on the real axis of the Smith chart in response to the fluctuation of the coupling coefficient of the electric field coupling formed by the power transmitting electrode unit and the power receiving electrode unit. Pre-designed . Then, a power transmitting inductor and a power receiving inductor having the designed inductance are used. This has the effect of enabling stable power transmission by electric field coupling while miniaturizing the electric field coupler formed by the power transmitting electrode unit and the power receiving electrode unit, even if the coupling coefficient fluctuates due to changes in the spacing or relative positions between the power transmitting electrode unit and the power receiving electrode unit.

[0016] According to a wireless power transmission system of claim 3, in a power transmitting device, high-frequency power generated by a high-frequency generating unit is output from a pair of power transmitting electrodes. The power output from the power transmitting electrodes is wirelessly received by the power receiving electrodes through electric field coupling when a pair of power receiving electrodes of a power receiving device provided in a mobile object are positioned opposite the power transmitting electrodes. The received power is supplied to a load provided in the mobile object. Here, a power transmitting-side feed point through which the power generated by the high-frequency generating unit is supplied to the power transmitting electrodes is provided at one end of the power transmitting electrodes formed by a flat conductor, and the other end is open. Meanwhile, a power receiving-side feed point of the power receiving electrode formed by a flat conductor, which supplies the received power to the load, is provided at one end on the other side of the power transmitting electrodes when facing the power transmitting electrodes, and the other end is open. In addition, the inductance of the power transmitting side inductor connected in series between the high frequency generating unit and the power transmitting electrode unit, the inductance of the power receiving side inductor connected in series between the power receiving electrode unit and the load, and the length of the transmission line between the high frequency generating unit and the power transmitting electrode unit are adjusted so that the reflection coefficient of the power seen from the high frequency generating unit changes on the real axis of the Smith chart in response to a change in the coupling coefficient of the electric field coupling formed by the power transmitting electrode unit and the power receiving electrode unit. Pre-designed . Then, a power transmitting inductor and a power receiving inductor having the designed inductance are used, and a transmission line is provided between the high frequency generating unit and the power transmitting electrode unit so as to have the designed transmission line length. This has the effect of enabling stable power transmission by electric field coupling while miniaturizing the electric field coupler formed by the power transmitting electrode unit and the power receiving electrode unit, even if the coupling coefficient fluctuates due to changes in the spacing or relative positions between the power transmitting electrode unit and the power receiving electrode unit.

[0017] The power transmitting device according to the fourth aspect of the present invention makes it possible to realize the wireless power transmission system according to any one of the first to third aspects of the present invention.

[0018] The power receiving device according to the fifth aspect of the present invention can realize the wireless power transmission system according to any one of the first to third aspects of the present invention.

[0019] The mobile object according to claim 6 includes the power receiving device according to claim 5, and thus can realize a mobile object that can enjoy the effects of the wireless power transmission system according to any one of claims 1 to 3. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1A is a schematic front view of a wireless power transmission system according to a first embodiment of the present invention, and FIG. 1B is a schematic plan view of a mobile object having a power receiving device of the wireless power transmission system. [Figure 2] 1A is a circuit configuration diagram of the wireless power transmission system, and FIG. 1B is a schematic diagram showing the size of a power transmission electrode portion of a power transmission device of the wireless power transmission system. [Figure 3] (a) is a schematic diagram of the electric field coupler used in the electromagnetic field analysis whose results are shown in (b), and (b) is a Smith chart showing the results of the electromagnetic field analysis when the distance between the power transmitting electrode and the power receiving electrode of the electric field coupler is changed. [Figure 4] 1(a) is a schematic diagram of the electric field coupler used in the electromagnetic field analysis whose results are shown in 1(b), and 1(b) is a Smith chart showing the results of the electromagnetic field analysis when the relative positions of the power transmitting electrode and the power receiving electrode in the electric field coupler are changed in the direction parallel to the short sides of each electrode. [Figure 5] 1(a) is a schematic diagram of the electric field coupler used in the electromagnetic field analysis whose results are shown in FIG. 1(b), and FIG. 1(b) is a Smith chart showing the results of the electromagnetic field analysis when the relative positions of the power transmitting electrode and the power receiving electrode in the electric field coupler are changed in the direction parallel to the long sides of the electrodes. [Figure 6] (a) is a schematic diagram of the electric field coupler used in the electromagnetic field analysis whose results are shown in (b) and (c), and (b) and (c) are Smith charts showing the results of the electromagnetic field analysis when the resistance value of the load connected to the power receiving electrode of the electric field coupler is changed. [Figure 7] FIG. 10 is a circuit configuration diagram of a wireless power transmission system according to a second embodiment. [Figure 8]1(a) is a Smith chart showing the reflection coefficient seen from the high-frequency generating unit when the coupling coefficient of the electric field coupler is varied from 0.00 to 0.99 in the wireless power transmission system with the inductances of the power transmitting inductor 13 and the power receiving inductor 23 set to zero and the transmission line length of the transmission line 14 set to zero; FIG. 1(b) is a Smith chart showing the reflection coefficient seen from the high-frequency generating unit when the coupling coefficient of the electric field coupler is varied from 0.00 to 0.99 in the wireless power transmission system with the inductances of the power transmitting inductor 13 and the power receiving inductor 23 adjusted; and FIG. 1(c) is a Smith chart showing the reflection coefficient seen from the high-frequency generating unit when the coupling coefficient of the electric field coupler is varied from 0.00 to 0.99 in the wireless power transmission system with the inductances of the power transmitting inductor 13 and the power receiving inductor 23 adjusted. [Figure 9] 8(a) is a schematic diagram of the electric field coupler used in the electromagnetic field analysis whose results are shown in FIG. 8(b), and FIG. 8(b) is a Smith chart showing the results of the electromagnetic field analysis when the distance between the power transmitting electrode and the power receiving electrode is changed after the inductances of the power transmitting inductor and the power receiving inductor connected to the electric field coupler and the transmission line length of the transmission line are set according to the procedure shown in FIG. 8. [Figure 10] 8(a) is a schematic diagram of the electric field coupler used in the electromagnetic field analysis whose results are shown in FIG. 8(b), and FIG. 8(b) is a Smith chart showing the results of the electromagnetic field analysis when the relative positions of the power transmitting electrode and the power receiving electrode are changed in the direction parallel to the short sides of the electrodes after the inductances of the power transmitting and power receiving inductors connected to the electric field coupler and the transmission line length of the transmission line are set according to the procedure shown in FIG. 8. [Figure 11] 8(a) is a schematic diagram of the electric field coupler used in the electromagnetic field analysis whose results are shown in FIG. 8(b), and FIG. 8(b) is a Smith chart showing the results of the electromagnetic field analysis when the relative positions of the power transmitting electrode and the power receiving electrode are changed in the direction parallel to the long sides of the electrodes after the inductances of the power transmitting and power receiving inductors connected to the electric field coupler and the transmission line length of the transmission line are set according to the procedure shown in FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Each of the embodiments described below illustrates a preferred specific example of the present invention. Therefore, the numerical values, shapes, materials, components, component placement and connection configurations, etc., shown in the following embodiments are merely examples and are not intended to limit the present invention. Therefore, among the components in the following embodiments, components that are not recited in the independent claims that represent the highest concept of the present invention will be described as optional components. Furthermore, in each drawing, substantially identical components are assigned the same reference numerals, and redundant explanations will be omitted or simplified.

[0022] (First embodiment) First, a schematic configuration of a wireless power transmission system 1 according to a first embodiment of the present invention will be described with reference to Fig. 1 and Fig. 2. Fig. 1(a) is a schematic front view of the wireless power transmission system 1, and Fig. 1(b) is a schematic plan view of a mobile object 30 having a power receiving device 20 of the wireless power transmission system 1. Fig. 2(a) is a circuit configuration diagram of the wireless power transmission system 1, and Fig. 2(b) is a schematic diagram showing the size of a power transmitting electrode unit 12 of a power transmitting device 10 of the wireless power transmission system 1.

[0023] The wireless power transmission system 1 is a system that transmits power wirelessly to a moving body 30 traveling on a traveling path 40, and as shown in Figure 1, it is composed of a power transmitting device 10 fixedly installed on the traveling path 40 and a power receiving device 20 provided on the moving body 30.

[0024] The moving body 30 is exemplified by an electric vehicle or an electric vehicle such as an unmanned automated guided vehicle (AGV), which operates automatically and without a driver, and has a battery 31, drive wheels 32, and driven wheels 33 in addition to the power receiving device 20. The moving body 30 drives the drive wheels 32 using the power stored in the battery 31, thereby traveling on the travel path 40. The battery 31 is an example of a load in the present invention.

[0025] The power transmission device 10 has, for example, a high-frequency generating unit 11 fixed to or embedded in the running path 40, and a pair of power transmission electrode units 12 composed of flat conductors embedded directly below the road surface of the running path 40.

[0026] The high frequency generating unit 11 is a high frequency inverter that generates high frequency power from commercial power.

[0027] The power transmitting electrode unit 12 outputs the power generated by the radio frequency generating unit 11. As shown in Fig. 3(a) described below, each of the power transmitting electrode units 12 has a power transmitting-side feeding point 12a at one end of a flat conductor, and the other end opposite the one end is open. The power generated by the radio frequency generating unit 11 is supplied to the power transmitting electrode unit 12 from the power transmitting-side feeding point 12a.

[0028] In the first embodiment, the size of the power transmitting electrode 12 is set so that when the power transmitting electrode 12 is equivalently converted into a transmission line, the length of the transmission line (transmission line length) is approximately ¼ of the wavelength λ of the power. For example, when a rectangular electrode (rectangular electrode) as shown in Fig. 2(b) is used as the power transmitting electrode 12, the length of the long side of the power transmitting electrode 12 is L1, the length of the short side is L2, and the length of the power feeding line that feeds the power generated by the high frequency generating unit 11 to the power transmitting electrode 12 is L3, the length L1 of the long side and the length L2 of the short side of the power transmitting electrode 12 and the length L3 of the power feeding line are set so that L1 + L2 + L3 ≈ λ / 4.

[0029] Here, the transmission line length of the power transmitting electrode 12 is the longest distance from the power transmitting-side feeding point 12a provided at one end of the power transmitting electrode 12 to the other end on the opposite side of the power transmitting electrode 12, that is, half the outer periphery length (L1 + L2) of the power transmitting electrode 12. In addition, since the power feeder is also considered to be a transmission line, the length L3 of the power feeder is added to the transmission line length of the power transmitting electrode 12.

[0030] The transmission line length of the power transmitting electrode portion 12 should be substantially 1 / 4 of the wavelength λ of the power to be transmitted, in other words, it should be a length that generates a phase difference of substantially π / 2 in the transmission line.

[0031] 1 and 2, the power receiving device 20 includes a power receiving electrode unit 21 and a rectifier circuit 22. The power receiving electrode unit 21 is provided as a pair on the underside of the moving body 30 at positions that can face the power transmitting electrode unit 12.

[0032] 3(a), which will be described later, each power receiving electrode 21 has a power receiving-side feed point 21a at one end thereof that is on the other end side (opposite the power transmitting-side feed point 12a) of the power transmitting electrode 12 when facing the power transmitting electrode 12, and the other end opposite to the one end (the side where the power transmitting-side feed point 12a of the power transmitting electrode 12 is located) is in an open state. The power receiving electrode 21 is connected to the battery 31 from the power receiving-side feed point 21a via the rectifier circuit 22.

[0033] Furthermore, in the first embodiment, the size of the power receiving electrode 21 is set so that when the power receiving electrode 21 is equivalently converted into a transmission line, the length of the transmission line (transmission line length) is approximately ¼ of the wavelength λ of power, similar to the power transmitting electrode 12. For example, when a rectangular electrode similar to the power transmitting electrode 12 shown in FIG. 2(b) is used as the power receiving electrode 21, the length of the long side of the power receiving electrode 21 is L4, the length of the short side is L5, and the length of the power feeder line that feeds the power received by the power receiving electrode 21 to the battery 31 is L6, the length L4 of the long side and the length L5 of the short side of the power receiving electrode 21, and the length L6 of the power feeder line are set so that L4 + L5 + L6 ≈ λ / 4.

[0034] The transmission line length of the power receiving electrode portion 21 also needs to be substantially 1 / 4 the wavelength λ of the transmitted power, in other words, it needs to be a length that generates a phase difference of substantially π / 2 in the transmission line.

[0035] The rectifier circuit 22 is a circuit that rectifies into direct current the high-frequency power output from the power receiving electrode 21. The power rectified into direct current by the rectifier circuit 22 is supplied to the battery 31, and the battery 31 is charged.

[0036] Next, the operation of the wireless power transmission system 1 according to the first embodiment will be described. When the moving object 30 travels along the travel path 40 and reaches a predetermined location where the power transmitter 10 is installed, the pair of power transmitting electrodes 12 of the power transmitter 10 and the pair of power receiving electrodes 21 of the power receiving device 20 face each other. The facing power transmitting electrodes 12 and power receiving electrodes 21 form an electric field coupler 50, as shown in FIG. 2 .

[0037] For example, when it is detected that the moving object 30 is present at the predetermined location, high-frequency power is generated by the high-frequency generating unit 11 and supplied to the power transmitting electrode unit 12 via the power transmitting-side feeding point 12a. The power supplied to the power transmitting electrode unit 12 is output to the power receiving electrode unit 21, and the power receiving electrode unit 21 wirelessly receives the power output from the power transmitting electrode unit 12 by electric field coupling.

[0038] The power received by the power receiving electrode 21 is output via the power receiving-side feeding point 21a, rectified from high frequency to direct current by the rectifier circuit 22, and then supplied to the battery 31 to charge the battery 31. In this way, the wireless power transmission system 1 can wirelessly and contactlessly transmit power from the power transmitting device 10 to the power receiving device 20 of the mobile object 30 to charge the battery 31. The mobile object 30 drives the drive wheels 32 using the power stored in the battery 31 and travels along the travel path 40.

[0039] In the wireless power transmission system 1 according to the first embodiment, as described above, when the power receiving electrode 21 and the power transmitting electrode 12 face each other, the power receiving-side feeding point 21a of the power receiving electrode 21 is provided on the opposite side to the power transmitting-side feeding point 12a of the power transmitting electrode 12 (the other end side where the power transmitting electrode 12 is in an open state). Also, the other end of the power receiving electrode 21 opposite to the one end where the power receiving-side feeding point 21a is provided is in an open state. Therefore, the electric field coupler 50 functions as an inverting coupler in which power with an inverted phase relative to the power output from the power transmitting electrode 12 is output from the power receiving electrode 21.

[0040] The phase difference generated between the power transmitting electrode 12 and the power receiving electrode 21 is θ, and the characteristic impedance of the even mode is Z 0e , the odd-mode characteristic impedance is Z 0o In this case, the Z matrix of the electric field coupler 50, which is an inverting coupler, is expressed by the following equation 1.

[0041]

number

[0042] Furthermore, the transmission line lengths of both the power transmitting electrode 12 and the power receiving electrode 21 are set to approximately ¼ of the wavelength λ of the high-frequency power. This causes the electric field coupler 50 to function as a λ / 4 inverting coupler, and a phase difference of π / 2 occurs between the power transmitting electrode 12 and the power receiving electrode 21. Therefore, the F matrix of the electric field coupler 50 is as shown in the following equation 2.

[0043]

number

[0044] The F matrix shown in Equation 2 has the same form as that of a gyrator. In other words, the electric field coupler 50, which is a λ / 4 inverting coupler, is equivalent to a gyrator. Therefore, even if the load resistance of the battery 31 varies depending on the state of charge or the coupling coefficient varies due to a shift in the relative position between the power transmitting electrode 12 and the power receiving electrode 21, the imaginary part of the input impedance seen from the high-frequency generating unit 11 does not vary. Therefore, even if the load or coupling coefficient varies, it is possible to prevent impedance mismatch from occurring, which could reduce power transmission efficiency, or prevent the high-frequency generating unit 11 from operating ideally, which could cause thermal damage to various elements.

[0045] 3 to 6, the coupling coefficient and load variation tolerance of the electric field coupler 50 (λ / 4 inverted coupler) of the wireless power transmission system 1 according to the first embodiment are shown using electromagnetic field analysis. Fig. 3(a) is a schematic diagram showing the electric field coupler 50 used in the electromagnetic field analysis whose results are shown in Fig. 3(b), and Fig. 3(b) is a Smith chart showing the results of the electromagnetic field analysis when the distance between the power transmitting electrode 12 and the power receiving electrode 21 in the electric field coupler 50 is changed.

[0046] 3(a), in the electric field coupler 50 used in the electromagnetic field analysis, each of the pair of power transmitting electrodes 12 and each of the pair of power receiving electrodes 21 are configured as rectangular electrodes, with the long side lengths (L1 and L4 above) being 300 mm and the short side lengths (L3 and L5 above) being 80 mm. The spacing between the pair of power transmitting electrodes 12 and the spacing between the pair of power receiving electrodes 21 are 10 mm, and therefore the length L3 of the power feeder line that feeds the power generated by the high-frequency generating unit 11 to the power transmitting electrode units 12 and the length L6 of the power feeder line that feeds the power received by the power receiving electrode units 21 to the battery 31 are set to 5 mm, which is half of 10 mm.

[0047] Therefore, in the electric field coupler 50 shown in Fig. 3(a), the transmission line lengths of the power transmitting electrode 12 and the power receiving electrode 21 are each 300 mm + 80 mm + 5 mm = 385 mm, so the power frequency that generates a phase difference of π / 2 in the 385 mm transmission line (the frequency at which the transmission line length is ¼ of the wavelength λ of the power) is calculated to be 195 MHz. However, because the electrode ends are at right angles, the actual transmission line length is shorter than 385 mm, and the frequency at which the phase difference is π / 2 is higher than 195 MHz. As a result of electromagnetic field analysis, a phase difference of π / 2 occurs at a frequency of approximately 200 MHz in the electric field coupler 50 shown in Fig. 3(a).

[0048] Although not shown, in the electromagnetic field analysis whose results are shown in FIG. 3(b), the resistance value of the load connected to the power receiving electrode 21 was set to 100Ω.

[0049] The Smith chart in FIG. 3(b) shows the results of electromagnetic field analysis of the reflection coefficient of the electric field coupler 50 shown in FIG. 3(a) when the distance between the power transmitting electrode 12 and the power receiving electrode 21 is changed from 10 mm to 100 mm. Specifically, the reflection coefficient at 200 MHz, at which a phase difference of π / 2 occurs between the power transmitting electrode 12 and the power receiving electrode 21 for each distance between the power transmitting electrode 12 and the power receiving electrode 21, is indicated by a black circle. As shown in FIG. 3(b), even when the distance between the power transmitting electrode 12 and the power receiving electrode 21 changes and the coupling coefficient of the electric field coupler 50 fluctuates, the reflection coefficient remains almost constant as a real part. Note that the ratio of the imaginary part to the real part (imaginary part / real part) of the reflection coefficient is preferably in the range of −1 to +1.

[0050] FIG. 4(a) is a schematic diagram showing the electric field coupler 50 used in the electromagnetic field analysis whose results are shown in FIG. 4(b), and FIG. 4(b) is a Smith chart showing the results of the electromagnetic field analysis when the relative positions of the power transmitting electrode 12 and the power receiving electrode 21 in the electric field coupler 50 are changed in a direction parallel to the short sides of each electrode.

[0051] The lengths of the long sides (L1, L4) and short sides (L2, L5) of the power transmitting electrode 12 and the power receiving electrode 21, the spacing (L3) between the pair of power transmitting electrodes 12, and the spacing (L6) between the pair of power receiving electrodes 21 used in the electromagnetic field analysis of Fig. 4(b) were the same as those shown in Fig. 3(a), and the spacing between the power transmitting electrode 12 and the power receiving electrode 21 was set to 20 mm. Although not shown, the resistance value of the load connected to the power receiving electrode 21 was set to 100 Ω.

[0052] 4(b) shows the results of electromagnetic field analysis of the reflection coefficient of the electric field coupler 50 when the relative positions of the power transmitting electrode 12 and the power receiving electrode 21 are changed from -80 mm to 80 mm in a direction parallel to the short sides of each electrode, with the position where the power transmitting electrode 12 and the power receiving electrode 21 completely overlap each other in a plan view being set to 0 mm in the electric field coupler 50 shown in FIG. 4(a). Specifically, the reflection coefficient at 200 MHz at which a phase difference of π / 2 occurs between the power transmitting electrode 12 and the power receiving electrode 21 for each relative position of the power transmitting electrode 12 and the power receiving electrode 21 is indicated by a black circle.

[0053] As shown in FIG. 4(b), even if the relative positions of the power transmitting electrode 12 and the power receiving electrode 21 change in the direction parallel to the short sides of each electrode and the coupling coefficient of the electric field coupler 50 fluctuates, it can be seen that the reflection coefficient remains almost in the real part.

[0054] FIG. 5(a) is a schematic diagram showing the electric field coupler 50 used in the electromagnetic field analysis whose results are shown in FIG. 5(b), and FIG. 5(b) is a Smith chart showing the results of the electromagnetic field analysis when the relative positions of the power transmitting electrode 12 and the power receiving electrode 21 in the electric field coupler 50 are changed in a direction parallel to the long sides of each electrode.

[0055] The lengths of the long sides (L1, L4) and short sides (L2, L5) of the power transmitting electrode 12 and the power receiving electrode 21, the spacing (L3) between the pair of power transmitting electrodes 12, and the spacing (L6) between the pair of power receiving electrodes 21 used in the electromagnetic field analysis of Fig. 5(b) were the same as those shown in Fig. 3(a), and the spacing between the power transmitting electrode 12 and the power receiving electrode 21 was set to 20 mm. Although not shown, the resistance value of the load connected to the power receiving electrode 21 was set to 100 Ω.

[0056] 5(b) shows the results of electromagnetic field analysis of the reflection coefficient of the electric field coupler 50 when the relative positions of the power transmitting electrode 12 and the power receiving electrode 21 are changed from -300 mm to 300 mm in a direction parallel to the long sides of each electrode, with the position where the power transmitting electrode 12 and the power receiving electrode 21 completely overlap each other in a plan view being set to 0 mm in the electric field coupler 50 shown in FIG. 5(a). Specifically, the reflection coefficient at 200 MHz at which a phase difference of π / 2 occurs between the power transmitting electrode 12 and the power receiving electrode 21 for each relative position of the power transmitting electrode 12 and the power receiving electrode 21 is indicated by a black circle.

[0057] As shown in FIG. 5(b), even if the relative positions of the power transmitting electrode 12 and the power receiving electrode 21 change in the direction parallel to the edge of each electrode and the coupling coefficient of the electric field coupler 50 fluctuates, it can be seen that the reflection coefficient remains almost in the real part.

[0058] FIG. 6(a) is a schematic diagram showing the electric field coupler 50 used in the electromagnetic field analysis whose results are shown in FIGS. 6(b) and 6(c), and FIGS. 6(b) and 6(c) are Smith charts showing the results of the electromagnetic field analysis when the resistance value of the load connected to the power-receiving electrode 21 in the electric field coupler 50 is changed.

[0059] The lengths of the long sides (L1, L4) and short sides (L2, L5) of the power transmitting electrode 12 and the power receiving electrode 21 used in the electromagnetic field analysis of Figure 6(b), the spacing (L3) between the pair of power transmitting electrode 12, and the spacing (L6) between the pair of power receiving electrode 21 were the same as those shown in Figure 3(a), and the spacing between the power transmitting electrode 12 and the power receiving electrode 21 was set to 20 mm.

[0060] The Smith charts in FIGS. 6(b) and 6(c) show the results of the reflection coefficient of the electric field coupler 50 obtained by electromagnetic field analysis when the resistance value of the load connected to the power-receiving electrode 21 in the electric field coupler 50 shown in FIG. 6(a) is changed from 1 Ω to 5000 Ω.

[0061] 6(b) shows by a ● the reflection coefficient at 200 MHz where a phase difference of π / 2 occurs between the power transmitting electrode 12 and the power receiving electrode 21 for each resistance value of the load connected to the power receiving electrode 21. As shown in FIG. 6(b), even if the load connected to the power receiving electrode 21 fluctuates, the reflection coefficient remains almost in the real part, although there is a slight deviation.

[0062] 6(c) also shows with a ● the reflection coefficient when the power frequency is 192 MHz for each resistance value of the load connected to the power receiving electrode 21. As shown in FIG. 6(c), it can be seen that by setting the power frequency to 192 MHz, the F matrix of the electric field coupler 50 becomes even closer to that of a gyrator. Therefore, in this case, even if the load connected to the power receiving electrode 21 fluctuates, the reflection coefficient can be maintained at a substantially real part.

[0063] As described above, in the wireless power transmission system 1 according to the first embodiment, the transmission line length of the power transmitting electrode 12 of the power transmitting device 10 and the transmission line length of the power receiving electrode 21 of the power receiving device 20 are set to ¼ of the wavelength λ of the power, and when the power transmitting electrode 12 and the power receiving electrode 21 are arranged opposite each other, the power receiving-side feeding point 21a of the power receiving electrode 21 is provided on the opposite side to the power transmitting-side feeding point 12a of the power transmitting electrode 12. As a result, the electric field coupler 50 is configured as a λ / 4 inverting coupler, and functions equivalently as a gyrator.

[0064] As a result, the wireless power transmission system 1 can suppress fluctuations in the imaginary part of the input impedance seen from the high-frequency generating unit 11 even if the resistance value of the load connected to the power receiving electrode 21 fluctuates or if the coupling coefficient of the electric field coupler 50 fluctuates due to changes in the distance or relative position between the power transmitting electrode 12 and the power receiving electrode 21. Therefore, even if the load or coupling coefficient fluctuates, it is possible to suppress impedance mismatching that could cause a decrease in power transmission efficiency or thermal damage to various elements due to the high-frequency generating unit 11 not performing ideal operation. As a result, the wireless power transmission system 1 can enable stable power transmission by electric field coupling without using a matching circuit for impedance matching.

[0065] Furthermore, since heat generation in the high-frequency generating unit 11 due to fluctuations in the load or coupling coefficient can be suppressed, a heat sink for dissipating the heat can be omitted or a simple one can be used. Furthermore, since heat generation in the high-frequency generating unit 11 due to fluctuations in the load or coupling coefficient can be suppressed, it is also possible to increase the power output of the high-frequency generating unit 11.

[0066] In addition, since there is no need for a matching circuit or a mechanism for controlling the element values ​​of the matching circuit based on fluctuations in input impedance, there is also the effect of being able to make the system more compact.

[0067] (Second embodiment) Next, the schematic configuration of a wireless power transmission system 1 according to the second embodiment will be described with reference to Fig. 7, focusing on the differences from the wireless power transmission system 1 according to the first embodiment. Fig. 7 is a circuit configuration diagram of the wireless power transmission system 1 according to the second embodiment. In Fig. 7, the same components as those in the wireless power transmission system 1 according to the first embodiment are denoted by the same reference numerals, and their description will be omitted here.

[0068] As in the first embodiment, in the wireless power transmission system 1 according to the second embodiment, the power transmitter 10 is fixedly installed on a road 40 on which a mobile object 30 travels, and the power receiver 20 is provided on the mobile object 30. When the power receiving electrode 21 and the power transmitting electrode 12 face each other, the power receiving-side feeding point 21a of the power receiving electrode 21 is provided on the opposite side to the power transmitting-side feeding point 12a of the power transmitting electrode 12 (the other end side where the power transmitting electrode 12 is in an open state), and the other end of the power receiving electrode 21 opposite to the one end where the power receiving-side feeding point 21a is provided is in an open state, so that the electric field coupler 50 functions as an inverting coupler, also as in the first embodiment.

[0069] In the wireless power transmission system 1 according to the first embodiment, a λ / 4 inverted coupler is formed as the electric field coupler 50 to achieve tolerance to fluctuations in the coupling coefficient of the electric field coupler 50 and fluctuations in the resistance value of the load. Therefore, when the frequency of the wirelessly transmitted power is set to a commonly used 13 MHz, the electrode sides of the power transmitting electrode 12 and the power receiving electrode 21 become large, measuring approximately 5.8 m. In the wireless power transmission system 1 according to the second embodiment, the tolerance to fluctuations is limited to the coupling coefficient of the electric field coupler 50, thereby reducing the size of the electrode sides of the power receiving electrode 21 in particular.

[0070] 7 , in the wireless power transmission system 1 according to the second embodiment, a power transmitting device 10 is provided with a power transmitting-side inductor 13 connected in series between a high-frequency generating unit 11 and each of a pair of power transmitting electrodes 12. A transmission line 14 can be added in series with the power transmitting-side inductor 13 between the high-frequency generating unit 11 and each of the power transmitting electrodes 12, so that the length of the transmission line between the high-frequency generating unit 11 and the power transmitting electrodes 12 can be adjusted. In addition, a power receiving device 20 is provided with a power receiving-side inductor 23 connected in series between each of a pair of power receiving electrodes 21 and a battery 31 (more specifically, a rectifier circuit 22 provided in front of the battery 31), which is a load connected to the wireless power transmission system 1.

[0071] 7 illustrates that the transmission line 14 can be added between the high-frequency generating unit 11 and the power transmitting inductor 13, but the transmission line 14 may also be configured to be added between the power transmitting inductor 13 and the power transmitting electrode unit 12. The addition of the transmission line 14 may be configured so that the transmission line 14 can be physically added in series with the power transmitting inductor 13, or the length of the transmission line between the high-frequency generating unit 11 and the power transmitting electrode unit 12 can be easily changed (extended) based on the design.

[0072] Next, referring to FIG. 8, a description will be given of a procedure for designing the inductances of the transmitting-side inductor 13 and the receiving-side inductor 23 and the transmission line length of the added transmission line 14 for the circuit of FIG. 7, assuming that the frequency of the power to be transmitted is 13 MHz and the size of the electric field coupler 50 is 1 / 40 of the wavelength λ of the power to be transmitted.

[0073] 8(a) is a Smith chart showing the reflection coefficient as seen from the high-frequency generating unit 11 when the coupling coefficient of the electric field coupler 50 is varied from 0.00 to 0.99, assuming that the inductances of the power transmitting inductor 13 and the power receiving inductor 23 are zero and the transmission line length of the transmission line 14 is zero under the above assumptions. This reflection coefficient can be obtained through electromagnetic field analysis or actual measurement.

[0074] As shown in FIG. 8(a), in this case, when the coupling coefficient of the electric field coupler 50 fluctuates, the imaginary part of the reflection coefficient changes significantly, causing impedance mismatch and reducing power transmission efficiency, and also preventing the high-frequency generating unit 11 from performing ideal operation, resulting in thermal destruction of various elements.

[0075] Therefore, the inductances of the power transmitting inductor 13 and the power receiving inductor 23 are adjusted. Fig. 8(b) is a Smith chart showing the reflection coefficient as seen from the high frequency generating unit 11 when the coupling coefficient of the electric field coupler 50 is varied from 0.00 to 0.99 in the case where the inductances of the power transmitting inductor 13 and the power receiving inductor 23 are adjusted under the above assumption. By adjusting the inductances of the power transmitting inductor 13 and the power receiving inductor 23, it may happen that the reflection coefficient changes to align on a straight line in the Smith chart in response to the variation in the coupling coefficient, as shown in Fig. 8(b).

[0076] Therefore, the inductances of the power transmitting inductor 13 and the power receiving inductor 23 are set so that the reflection coefficient changes in a straight line in response to a change in the coupling coefficient on the Smith chart. Here, the reflection coefficient does not necessarily have to be aligned on a straight line in absolute terms in response to a change in the coupling coefficient; it is sufficient if the reflection coefficient can be considered to be substantially aligned on a straight line. For example, when a straight approximation line is drawn for the reflection coefficient on the Smith chart, it is preferable that the ratio of the imaginary part to the real part (imaginary part / real part) be within the range of -1 to +1. In this example, when the inductance of the power transmitting inductor 13 and the power receiving inductor 23 is 3800 nH, the reflection coefficient changes in a straight line in response to a change in the coupling coefficient, as shown in the Smith chart in FIG. 8(b).

[0077] Next, the transmission line length of the added transmission line 14 is adjusted. Fig. 8(c) is a Smith chart showing the reflection coefficient as seen from the high-frequency generating unit 11 when the coupling coefficient of the electric field coupler 50 is varied from 0.00 to 0.99 in the case where the transmission line length of the transmission line 14 is adjusted under the above assumption. By adjusting the transmission line length of the transmission line 14, as shown in Fig. 8(c) in the Smith chart, the imaginary part of the reflection coefficient becomes constant with respect to the variation in the coupling coefficient, and the reflection coefficient changes on the real axis.

[0078] Therefore, the transmission line length of the transmission line 14 is set so that the reflection coefficient changes on the real axis in response to a change in the coupling coefficient in the Smith chart shown in FIG. 8(c). Here, the reflection coefficient changing on the real axis in response to a change in the coupling coefficient means that the reflection coefficient changes substantially on the real axis, and does not necessarily change absolutely on the real axis. For example, it is preferable that the ratio of the imaginary part to the real part of the reflection coefficient (imaginary part / real part) falls within the range of −1 to +1. In this example, the transmission line length of the transmission line 14 is set to a length that generates a phase difference of 5°, so that the reflection coefficient changes on the real axis in response to a change in the coupling coefficient in the Smith chart shown in FIG. 8(c).

[0079] It should be noted that, at the stage where the inductances of the power transmitting inductor 13 and the power receiving inductor 23 are adjusted (the stage shown in FIG. 8(b)), even if the coupling coefficient varies, the imaginary part of the reflection coefficient may remain constant, and the reflection coefficient may actually vary on the real axis. In this case, it is possible to omit adding the transmission line 14 (the stage shown in FIG. 8(c)).

[0080] 8, a Smith chart was used to set the inductances of the power transmitting-side inductor 13 and the power receiving-side inductor 23, and the transmission line length of the transmission line 14 between the high-frequency generating unit 11 and the power transmitting electrode unit 12. However, it is not necessary to use a Smith chart for these settings, and it is sufficient if the reflection coefficient seen from the high-frequency generating unit 11 changes on the real axis of the Smith chart in response to fluctuations in the coupling coefficient of the electric field coupler 50 as a result of these settings.

[0081] Next, with reference to FIGS. 9 to 11, the results of electromagnetic field analysis will be used to show the tolerance to fluctuations in the coupling coefficient of the electric field coupler 50 in which the power transmitting-side inductor 13 and the power receiving-side inductor 23, whose inductances are set as shown in FIG. 8, are connected to the transmission line 14, whose transmission line length is set.

[0082] First, FIG. 9(a) is a schematic diagram showing the electric field coupler 50 used in the electromagnetic field analysis whose results are shown in FIG. 9(b), and FIG. 9(b) is a Smith chart showing the results of the electromagnetic field analysis when the distance between the power transmitting electrode 12 and the power receiving electrode 21 is changed after the inductances of the power transmitting-side inductor 13 and the power receiving-side inductor 23 connected to the electric field coupler 50 and the transmission line length of the transmission line 14 are set according to the procedure shown in FIG. 8.

[0083] 9(a), the electric field coupler 50 used in the electromagnetic field analysis has a pair of power transmitting electrodes 12 and a pair of power receiving electrodes 21, each of which is formed of a rectangular electrode, with the long side lengths (L1 and L4 above) being 500 mm and the short side lengths (L3 and L5 above) being 70 mm. The distance between the pair of power transmitting electrodes 12 and the distance between the pair of power receiving electrodes 21 were 10 mm. For this electric field coupler 50, the power frequency was set to 13 MHz, and the inductances of the power transmitting-side inductor 13 and the power receiving-side inductor 23 to be connected and the transmission line length of the transmission line 14 were set using the procedure shown in FIG.

[0084] 9(b), the Smith chart shows, by marks ●, the results of electromagnetic field analysis of the reflection coefficient of the electric field coupler 50 when the distance between the power transmitting electrode 12 and the power receiving electrode 21 is changed from 10 mm to 100 mm. As shown in Fig. 9(b), even when the distance between the power transmitting electrode 12 and the power receiving electrode 21 changes and the coupling coefficient of the electric field coupler 50 fluctuates, the reflection coefficient moves substantially along the horizontal axis (real axis).

[0085] 10(a) is a schematic diagram of the electric field coupler 50 used in the electromagnetic field analysis whose results are shown in FIG. 10(b). FIG. 10(b) is a Smith chart showing the results of the electromagnetic field analysis when the relative positions of the power transmitting electrode 12 and the power receiving electrode 21 are changed in the direction parallel to the short sides of the electrodes after the inductances of the power transmitting-side inductor 13 and the power receiving-side inductor 23 to be connected and the transmission line length of the transmission line 14 are set in the electric field coupler 50 according to the procedure shown in FIG. 8.

[0086] 10(a), the lengths of the long sides (L1, L4) and short sides (L2, L5) of the power transmitting electrode 12 and the power receiving electrode 21, the spacing (L3) between the pair of power transmitting electrodes 12, and the spacing (L6) between the pair of power receiving electrodes 21 used in the electromagnetic field analysis of Fig. 10(b) were the same as those shown in Fig. 9(a), and the spacing between the power transmitting electrode 12 and the power receiving electrode 21 was set to 20 mm. The inductances of the connected power transmitting-side inductor 13 and power receiving-side inductor 23 and the transmission line length of the transmission line 14 were also set to the same values ​​as those used in the electromagnetic field analysis of Fig. 9(b).

[0087] 10(b), the position where the power transmitting electrode unit 12 and the power receiving electrode unit 21 completely overlap in a plan view is set to 0 mm, and the results of the reflection coefficient of the electric field coupler 50 obtained by electromagnetic field analysis when the relative position of the power transmitting electrode unit 12 and the power receiving electrode unit 21 is changed from 0 mm to 80 mm in a direction parallel to the short sides of each electrode are indicated by ●. As shown in Fig. 10(b), even if the relative position of the power transmitting electrode unit 12 and the power receiving electrode unit 21 changes in a direction parallel to the short sides of each electrode unit and the coupling coefficient of the electric field coupler 50 varies, it can be seen that the reflection coefficient moves substantially along the horizontal axis (real axis).

[0088] FIG. 11(a) is a schematic diagram of the electric field coupler 50 used in the electromagnetic field analysis whose results are shown in FIG. 11(b). FIG. 11(b) is a Smith chart showing the results of the electromagnetic field analysis when the relative positions of the power transmitting electrode 12 and the power receiving electrode 21 are changed in the direction parallel to the long sides of the electrodes after the inductances of the power transmitting-side inductor 13 and the power receiving-side inductor 23 to be connected and the transmission line length of the transmission line 14 in the electric field coupler 50 are set according to the procedure shown in FIG. 8.

[0089] 11(a), the lengths of the long sides (L1, L4) and short sides (L2, L5) of the power transmitting electrode 12 and the power receiving electrode 21, the spacing (L3) between the pair of power transmitting electrodes 12 and the spacing (L6) between the pair of power receiving electrodes 21, and the spacing between the power transmitting electrode 12 and the power receiving electrode 21 used in the electromagnetic field analysis of Fig. 11(b) were the same as those shown in Fig. 10(a). In addition, the inductances of the connected power transmitting-side inductor 13 and power receiving-side inductor 23 and the transmission line length of the transmission line 14 were set to the same values ​​as those used in the electromagnetic field analysis of Fig. 10(b).

[0090] 11(b), the position where the power transmitting electrode unit 12 and the power receiving electrode unit 21 completely overlap in a plan view is set to 0 mm, and the results of the reflection coefficient of the electric field coupler 50 obtained by electromagnetic field analysis when the relative position of the power transmitting electrode unit 12 and the power receiving electrode unit 21 is changed from 0 mm to 500 mm in a direction parallel to the long sides of each electrode are indicated by ●. As shown in Fig. 11(b), even if the relative position of the power transmitting electrode unit 12 and the power receiving electrode unit 21 changes in a direction parallel to the long sides of each electrode unit and the coupling coefficient of the electric field coupler 50 varies, it can be seen that the reflection coefficient moves substantially along the horizontal axis (real axis).

[0091] As described above, the wireless power transmission system 1 according to the second embodiment is configured such that the power transmitting device 10 has the power transmitting-side inductors 13 connected in series between the high-frequency generating unit 11 and each of the pair of power transmitting electrodes 12, the power receiving device 20 has the power receiving-side inductors 23 connected in series between each of the pair of power receiving electrodes 21 and the battery 31 as a load, and further has a transmission line 14 that can be added in series with the power receiving-side inductor 23. Then, using electromagnetic field analysis or the like, the inductances of the power transmitting-side inductor 13 and the power receiving-side inductor 23 and the transmission line length of the transmission line 14 are set so that the reflection coefficient seen from the high-frequency generating unit 11 changes on the real axis in response to fluctuations in the coupling coefficient of the electric field coupler 50.

[0092] As a result, in the electric field coupler 50, which is smaller than ¼ of the wavelength λ of power, even if the coupling coefficient of the electric field coupler 50 varies due to changes in the spacing or relative positions between the power transmitting electrode 12 and the power receiving electrode 21, it is possible to suppress fluctuations in the imaginary part of the input impedance seen from the high-frequency generating unit 11. This makes it possible to suppress impedance mismatches caused by fluctuations in the coupling coefficient, which can reduce power transmission efficiency, and thermal damage to various elements caused by the high-frequency generating unit 11 not performing ideal operation. Therefore, the wireless power transmission system 1 can enable stable power transmission by electric field coupling while miniaturizing the electric field coupler 50.

[0093] In this case, it is possible to match the input impedance to the load fluctuations by using a DC / DC converter or the like.

[0094] Furthermore, since heat generation in the high-frequency generating unit 11 due to fluctuations in the coupling coefficient can be suppressed, a heat sink for dissipating the heat can be omitted or a simple one can be used. Furthermore, since heat generation in the high-frequency generating unit 11 due to fluctuations in the coupling coefficient can be suppressed, it is also possible to increase the power output of the high-frequency generating unit 11.

[0095] In addition, since there is no need for a mechanism to control the element values ​​of the matching circuit based on fluctuations in the coupling coefficient, there is also the effect of being able to make the system more compact.

[0096] 9 to 11, it is assumed that the power transmitting electrode unit 12 and the power receiving electrode unit 21 have the same dimensions, but in the wireless power transmission system 1 according to the second embodiment, the power transmitting electrode unit 12 and the power receiving electrode unit 21 do not necessarily have to have the same dimensions. Even if the power transmitting electrode unit 12 and the power receiving electrode unit 21 have different sizes, by setting the inductances of the power transmitting-side inductor 13 and the power receiving-side inductor 23 and the transmission line length of the transmission line 14 according to the procedure shown in Fig. 8, even if the spacing or relative positions between the power transmitting electrode unit 12 and the power receiving electrode unit 21 change and the coupling coefficient of the electric field coupler 50 changes, it is possible to suppress fluctuations in the imaginary part of the input impedance seen from the high-frequency generating unit 11.

[0097] In particular, since the power transmitting electrode unit 12 is installed on the travel path 40, there may be cases where miniaturization is not required. Therefore, the power transmitting electrode unit 12 may be made larger than the power receiving electrode unit 21 while miniaturizing the power receiving electrode unit 21. In this case, the power receiving device 20 can be made smaller, and the wireless power transmission system 1 can be constructed for a small mobile object 30. Furthermore, by making the power transmitting electrode unit 12 larger than the power receiving electrode unit 21, the range of misalignment between the power transmitting electrode unit 12 and the power receiving electrode unit 21 can be reduced, which has the effect of reducing the possibility of the coupling coefficient varying depending on the location where the mobile object 30 stops for power supply.

[0098] The present invention has been described above based on an embodiment, but the present invention is not limited to the above embodiment, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention.

[0099] For example, each embodiment may be modified by adding a part or parts of the configuration of another embodiment to that embodiment, or by replacing a part or parts of the configuration of that embodiment with that embodiment, etc. Furthermore, the numerical values ​​given in the above embodiments are merely examples, and it is of course possible to adopt other numerical values.

[0100] In the above embodiment, the mobile object 30 travels on the travel path 40, but the present invention is not limited to this and may be an object that travels on water, underwater, or in the air, such as a drone. In this case, the wireless power transmission system 1 may be installed with the power transmitter 10 fixed at a location where the mobile object 30 can be moored or parked.

[0101] In the above embodiment, the battery 31 is exemplified as an example of a load of the present invention. However, the load is not limited to the battery 31 and may be, for example, a device that is driven or operated by electric power. For example, a motor is one example. In this case, a system is conceivable in which the mobile object 30 moves to a predetermined location, and then receives power from the power transmitting device 10 via the power receiving device 20, and drives the motor provided in the mobile object 30. [Explanation of symbols]

[0102] 1. Wireless power transmission system 10 Power transmission equipment 11 High frequency generation section 12 Power transmission electrode part 12a Power supply point on the transmission side 13 Transmission side inductor 14 Transmission Lines 20 Power receiving device 21 Power receiving electrode part 21a Receiving power supply point 22 Rectifier circuit 23 Receiving side inductor 30 Mobile 31 Battery 50 Electric field coupler

Claims

1. A wireless power transmission system including a power transmission device and a power receiving device provided on a mobile body that can move relative to the power transmission device, the system wirelessly transmitting power from the power transmission device to the power receiving device by electric field coupling, The power transmission device is a high frequency generating unit that generates high frequency power; a pair of power transmission electrodes configured by flat, rectangular conductors having a power transmission-side feed point at one end and an open end at the other end, the power transmission electrodes outputting power generated by the high-frequency generation unit and supplied from the power transmission-side feed point; The power receiving device is a pair of power receiving electrodes provided at positions that can face the power transmitting electrode unit, the power receiving electrode unit having a power receiving-side feed point at one end that is located on the other end side of the power transmitting electrode unit when facing the power transmitting electrode unit, and the other end being formed of a flat, rectangular conductor that is in an open state, the power receiving electrode unit receiving power output from the power transmitting electrode unit by electric field coupling, and feeding the power received from the power receiving-side feed point to a load provided on the mobile body, A wireless power transmission system characterized in that when the transmitting electrode unit and the receiving electrode unit are each equivalently converted into a transmission line, the length of the transmission line is 1 / 4 of the wavelength of the power to be transmitted.

2. A wireless power transmission system including a power transmission device and a power receiving device provided on a mobile body that can move relative to the power transmission device, the system wirelessly transmitting power from the power transmission device to the power receiving device by electric field coupling, The power transmission device is a high frequency generating unit that generates high frequency power; a pair of power transmission electrode units each having a power transmission-side feed point at one end and a flat conductor with the other end in an open state, the power transmission electrode units outputting power generated by the high-frequency generating unit and supplied from the power transmission-side feed point; a power transmitting inductor connected in series between the high frequency generating unit and the power transmitting electrode unit, The power receiving device is a pair of power receiving electrodes provided at positions that can face the power transmitting electrode unit, the power receiving electrode unit having a power receiving-side feed point at one end that is located on the other end side of the power transmitting electrode unit when facing the power transmitting electrode unit, and the other end being formed of a flat conductor that is in an open state, the power receiving electrode unit receiving power output from the power transmitting electrode unit by electric field coupling, and feeding the power received from the power receiving-side feed point to a load provided in the mobile body; a power receiving inductor connected in series between the power receiving electrode unit and the load, A wireless power transmission system characterized in that the inductances of the transmitting side inductor and the receiving side inductor are designed in advance so that the reflection coefficient of power seen from the high-frequency generating unit changes on the real axis of a Smith chart in response to fluctuations in the coupling coefficient of the electric field coupling formed by the transmitting electrode unit and the receiving electrode unit, and the transmitting side inductor and the receiving side inductor having the designed inductance are used.

3. A wireless power transmission system including a power transmission device and a power receiving device provided on a mobile body that can move relative to the power transmission device, the system wirelessly transmitting power from the power transmission device to the power receiving device by electric field coupling, The power transmission device is a high frequency generating unit that generates high frequency power; a pair of power transmission electrode units each having a power transmission-side feed point at one end and a flat conductor with the other end in an open state, the power transmission electrode units outputting power generated by the high-frequency generating unit and supplied from the power transmission-side feed point; a power transmitting inductor connected in series between the high frequency generating unit and the power transmitting electrode unit, The power receiving device is a pair of power receiving electrodes provided at positions that can face the power transmitting electrode unit, the power receiving electrode unit having a power receiving-side feed point at one end that is located on the other end side of the power transmitting electrode unit when facing the power transmitting electrode unit, and the other end being formed of a flat conductor that is in an open state, the power receiving electrode unit receiving power output from the power transmitting electrode unit by electric field coupling, and feeding the power received from the power receiving-side feed point to a load provided in the mobile body; a power receiving inductor connected in series between the power receiving electrode unit and the load, a transmission line length between the high-frequency generating unit and the power transmitting electrode unit, wherein the inductances of the power transmitting side inductor and the power receiving side inductor and the transmission line length between the high-frequency generating unit and the power transmitting electrode unit are designed in advance so that the reflection coefficient of power seen from the high-frequency generating unit changes on the real axis of a Smith chart in response to fluctuations in the coupling coefficient of the electric field coupling formed by the power transmitting electrode unit and the power receiving electrode unit; the power transmitting side inductor and the power receiving side inductor having the designed inductances are used; and a transmission line is provided between the high-frequency generating unit and the power transmitting electrode unit so as to have the designed transmission line length.

4. A power transmitting device used in the wireless power transmission system according to claim 1 .

5. A power receiving device used in the wireless power transmission system according to claim 1 .

6. A mobile object comprising the power receiving device according to claim 5.

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