Wireless power supply system

Abstract

The present invention provides a wireless power supply system using PT symmetry, wherein adjustment or control of the positions and angles of a power supply coil and a power reception coil is unnecessary, the structure is simple, and it is possible to constantly supply power wirelessly in a state in which the positional relationship between the power supply coil and the power reception coil is limited as little as possible and has further allowance than existing technologies, without the power supply being interrupted even when the positions and angles of the two coils deviate or separate slightly.　Provided is a wireless power supply system using PT symmetry, the wireless power supply system comprising a power supply circuit provided with a power supply coil and a power reception circuit provided with a power reception coil, and the power supply circuit and the power reception circuit each having a resonance circuit. In the configuration of the resonance circuit in the power reception circuit, the power reception coil and two capacitors are connected in series, and a rectification circuit is connected to both ends of either one of the two capacitors.

Description

Wireless Power Supply System

[0001] The present invention relates to a wireless power supply system that utilizes parity-time symmetry (hereinafter referred to as "PT symmetry").

[0002] There are several known contactless wireless power transfer technologies, including electromagnetic induction and magnetic resonance. Of these, electromagnetic induction wireless power transfer technology is used, for example, to charge mobile phones, and has coils arranged one above the other, essentially acting as an electrical transformer, with electricity flowing when the power transfer coil and power receiving coil are tightly attached.

[0003] However, with electromagnetic induction wireless power transfer technology, it is not possible to maintain a large distance between the power transfer coil and the power receiving coil, and even a slight misalignment or separation between the power transfer coil and the power receiving coil makes it impossible to charge or transfer power. This makes it difficult to apply this technology to artificial devices attached to the human body, such as artificial hearts, or to devices that rotate in multiple directions or have an axis that is misaligned, such as robotic arms.

[0004] Furthermore, magnetic resonance wireless power transfer technology was developed at a university in the United States around 2006-2007, and is close to being put to practical use because it allows for a greater distance between the power supply coil and the power receiving coil compared to electromagnetic induction. However, it is sensitive in that it cannot be transferred unless the distance between the power supply coil and the power receiving coil is kept constant, and it cannot be transferred if the coils are closer or farther apart than that distance, or if they are at an angle. This also poses the problem of it being difficult to apply this technology to artificial devices attached inside the human body, such as artificial hearts, or to devices that rotate in multiple directions or have an axis that is misaligned, such as robotic arms.

[0005] In order to solve such problems, for example, Patent Document 1 discloses a contactless power supply system using the magnetic resonance method, which uses a wireless power supply technology based on magnetic resonance and includes a control device that has the function of adjusting the positional relationship between a power supply coil and a power receiving coil and adjusting the angle, thereby supplying stable power to an artificial heart or the like.

[0006] Furthermore, for example, Patent Document 2 discloses a technology for a contactless power supply type rotation module used in a robot, in which a multi-joint robot having a first arm and a second arm has two contactless power supply parts to facilitate work such as attaching or adding arms, thereby enabling rotation and bending.

[0007] International Publication No. 2018 / 150678 Japanese Patent Application Laid-Open No. 2020-106985 Japanese Patent Application Laid-Open No. 2022-121324

[0008] Sid Assawaworrarit, Xiaofang Yu & Shanhui Fan, “Robust wireless power transfer using a nonlinear parity-time-symmetric circuit”, Nature, 15 JUNE 2017, volume 546, p.387-390Xianglin Hao, Ke Yin, Jianlong Zou, Ruibin Wang, Yuangen Huang, Xikui Ma & Tianyu Dong, “Frequency-Stable Robust Wireless Power 2023, 130, 077202J. Zhou, B. Zhang, W. Xiao, D. Qiu, and Y. Chen, “Nonlinear parity-time-symmetric model for constant efficiency wireless power transfer: application to a drone-in-flight wireless charging platform”, IEEE Trans. Ind. Electron., Aug. 2019, vol.66, no.5, pp.4097-4107H. Ishida, T. Kyoden, and H. Furukawa, “Application of parity-time symmetry to low-frequency wireless power transfer system”, IEEJ J. Ind. Appl., 2022, vol.11, no.1, pp.59-68Isamu Takahashi and Kazuo Hori, “Improvement of input current waveform of diode rectifier circuit using passive elements”, IEEJ Transactions on Power Electronics, 1997, 117(1), pp.13-18

[0009] However, in a contactless power transfer system using magnetic resonance as disclosed in, for example, Patent Document 1, it is necessary to provide a function for adjusting the distance and angle between the power supply coil and the power receiving coil so that they remain constant, which causes problems such as the power transmitting device becoming large in size and the need to constantly perform advanced control such as adjusting the positional relationship and angle between the coils, which places a burden on the control unit of the power transmitting device.In addition, there is also a problem that the advanced control function stops when the battery is replaced.

[0010] Furthermore, in a contactless power supply system for a robot arm as shown in, for example, Patent Document 2, when power is supplied to or received from a rotating object, if the power supply coil rotates in conjunction with the rotation of the object to be supplied with power, there is a problem that power cannot be supplied at a certain rotation angle. Also, since it is not possible to have a single arm whose tip can bend in any direction and rotate 360 ​​degrees in any direction, there is also a problem that if 360-degree rotation is desired, a complex structure with multiple joints is required.

[0011] The present invention has been made to solve the above-mentioned problems, and has an object to provide a wireless power transfer system that utilizes PT symmetry, which does not require adjustment or control of the positions and angles of the power transfer coil and the power receiving coil, has a simple structure, and is capable of constantly supplying power wirelessly without interruption even if the positions and angles of the power transfer coil and the power receiving coil are slightly misaligned or separated, and which places as few restrictions as possible on the positional relationship between the two coils with more leeway than conventional systems.

[0012] In order to achieve the above object, the present invention provides a wireless power supply system that utilizes Parity-Time symmetry (hereinafter referred to as "PT symmetry"), comprising a power supply circuit provided with a power supply coil and a power receiving circuit provided with a power receiving coil, and the power supply circuit and the power receiving circuit each have a resonant circuit, and as a means for always supplying power wirelessly while preserving the PT symmetry and keeping the transmitted power constant, the resonant circuit in the power receiving circuit is configured so that the power receiving coil and two capacitors are connected in series, and a rectifier circuit is connected across either one of the two capacitors.

[0013] The present invention also provides a wireless power supply system that utilizes parity-time symmetry (hereinafter referred to as "PT symmetry"), comprising a power supply circuit provided with a power supply coil and a power receiving circuit provided with a power receiving coil, wherein the power supply circuit and the power receiving circuit each have a resonant circuit, and as means for always supplying power wirelessly while preserving the PT symmetry and keeping the transmitted power constant, the resonant circuit in the power receiving circuit is configured so that a rectifier circuit is connected to the resonant circuit, and the rectifier circuit has a power factor correction circuit provided between the rectifier diode and the smoothing capacitor, and the power factor of the power factor correction circuit is adjusted to be between 0.6 and 1.0.

[0014] The present invention also provides a wireless power supply system that utilizes Parity-Time symmetry (hereinafter referred to as "PT symmetry"), comprising a power supply circuit provided with a power supply coil, and a power receiving circuit provided with a power receiving coil, wherein the power supply circuit and the power receiving circuit each have a resonant circuit, and as means for always supplying power wirelessly while preserving the PT symmetry and keeping the transmitted power constant, the resonant circuit in the power receiving circuit is configured so that a rectifier circuit is connected to the resonant circuit, and a step-down chopper type DC-DC converter is provided in a stage subsequent to the rectifier circuit, and the value of the AC equivalent load resistance connected to the resonant circuit in the power receiving circuit is adjusted depending on the value of the duty ratio D of this DC-DC converter.

[0015] According to the wireless power feed system of the present invention, in wireless power feed utilizing PT symmetry, there is no need to adjust or control the positions and angles of the feed coil and the receive coil, and the structure is simple. Furthermore, high transmission efficiency can be maintained without interruption even if the positions and angles of the feed coil and the receive coil are slightly misaligned or separated. Therefore, it is possible to constantly supply power wirelessly with as few restrictions as possible on the positional relationship between the two coils, with even more leeway than before.

[0016] In a rotating power supply target in a wireless power supply system using PT symmetry, the positional relationship between the coils when the center of rotation O is at the center of the receiving coil, and the rotation angle θ and magnetic coupling coefficient k ｍ 1 is a diagram showing the relationship between the positional relationship between the coils when the center of rotation O is located at one of two magnetic poles at both ends of a solenoid-type power receiving coil in a rotating power supply target in a wireless power supply system utilizing PT symmetry according to the first embodiment of the present invention, and the relationship between the rotation angle and the magnetic coupling coefficient k ｍ 1A is a graph showing the relationship between the rotation angle of two coils (a power supply coil and a power receiving coil) used in a wireless power supply system and the transmitted power. FIG. 1B is an explanatory diagram showing an example of the schematic configuration of a wireless power supply system. FIG. 1C is a graph showing the relationship between the rotation angle of two coils (a power supply coil and a power receiving coil) used in a wireless power supply system and the transmitted power. FIG. 1D is a diagram showing the relationship between the magnetic coupling coefficient k ｍ , critical magnetic coupling coefficient k ｍｃ、and an example graph of experimental results showing the relationship between transmitted power.

[0033] FIG. 13 is a conceptual diagram showing the circuit configuration of a conventional wireless power feed system using a magnetic resonance method utilizing PT symmetry.

[0034] FIG. 14 is a conceptual diagram showing an example of the circuit configuration of a wireless power feed system using a magnetic resonance method utilizing PT symmetry according to embodiment 1 of the present invention.

[0035] FIG. 15 is a conceptual diagram showing another example of the circuit configuration of a wireless power feed system using a magnetic resonance method utilizing PT symmetry according to embodiment 1 of the present invention.

[0036] FIG. 16 is a circuit diagram showing an example of a receiving circuit of a wireless power feed system using a magnetic resonance method utilizing PT symmetry according to embodiment 2 of the present invention.

[0037] FIG. 17 is a simulation circuit for comparatively verifying the effects of the choke coil according to embodiment 2 of the present invention.

[0038] FIG. 18 is a circuit diagram showing another example of a receiving circuit of a wireless power feed system using a magnetic resonance method utilizing PT symmetry according to embodiment 2 of the present invention.

[0039] FIG. 19 is a table of experimental results showing the relationship between power factor and whether or not the coil can be rotated in the receiving circuit shown in FIG. 12.

[0039] FIG. 19 is a diagram showing a relationship between the power factor and whether or not the coil can be rotated in the receiving circuit shown in FIG. ｍ 1 is a graph showing the relationship between the power supply distance and the power transmission distance between two coils (a power supply coil and a power receiving coil). FIG. 2 is a graph showing the experimental results of the power transmission distance and the power transmission distance between two coils (a power supply coil and a power receiving coil). FIG. 3 is a graph showing the experimental results of the power transmission distance and the power transmission distance between two coils (a power supply coil and a power receiving coil). FIG. 4 is a schematic perspective view and an internal perspective view showing an example in which the wireless power supply systems according to first to third embodiments of the present invention are applied to a motor.

[0017] The present invention relates to a wireless power supply system that utilizes parity-time symmetry (hereinafter referred to as "PT symmetry"). Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0018] First, we will explain wireless power transfer technology. There are several known wireless power transfer technologies, such as electromagnetic induction and magnetic resonance. Of these, electromagnetic induction wireless power transfer technology is used, for example, to charge mobile phones. In this technology, the coils are arranged one above the other, and, based on the same principle as a transformer, power can be transferred only when the distance (transmission distance) between the power transfer coil and the power receiving coil is very short.

[0019] However, because the transmission distance of electromagnetic induction wireless power transfer technology is short, at around a few millimeters, the distance between the power transfer coil and the power receiving coil cannot be large. Furthermore, even a slight misalignment or separation between the power transfer coil and the power receiving coil makes charging and power transfer impossible. In other words, because this technology is sensitive to misalignment, it is difficult to apply it to artificial devices attached inside the human body, such as artificial hearts, or to devices that rotate in multiple directions or have an axis that is misaligned, such as robotic arms.

[0020] Furthermore, magnetic resonance wireless power transfer technology has a long transmission distance of several centimeters to several meters, which allows for a greater distance between the power supply coil and the power receiving coil compared to electromagnetic induction, and it is close to being put to practical use. However, power cannot be transferred unless the distance between the power supply coil and the power receiving coil is kept constant, and if the coils are closer or further away than that distance, or if they are at an angle, the transmission efficiency decreases and the required power cannot be sent. In other words, this method is also vulnerable to positional misalignment, making it difficult to apply to devices that rotate in multiple directions or have an axis misalignment (rotating power supply targets), such as robot arms.

[0021] Furthermore, Patent Document 1 discloses a wireless power supply system that uses magnetic field resonance wireless power supply technology and is equipped with a control device that has the function of adjusting the positional relationship between the power supply coil and the power receiving coil, as well as adjusting the angle, to supply stable power to an auxiliary artificial heart, etc. According to this system, even if the position shifts up or down by a few centimeters due to human body movement, the control device adjusts the position each time by changing parameters, etc., to match the position shift.

[0022] However, this type of system requires functions to adjust the distance and angle between the power supply coil and the power receiving coil to a constant, which results in the control device (external device such as a power transmission device) becoming large-scale, and the need to constantly perform advanced control such as adjusting the positional relationship and angle between the coils places a burden on the control unit of the control device (external device such as a power transmission device).Another problem is that this advanced control function stops when the battery used to supply power to the external device is replaced.

[0023] For this reason, there is a strong demand for a wireless power transfer system that does not require adjustment or control of the positions and angles of the power transfer coil and power receiving coil for a rotating target, and that can supply power wirelessly without interruption no matter how much the power receiving coil rotates relative to the power transfer coil. Experiments and verifications have been conducted repeatedly on various wireless power transfer methods, but at present no system suitable for practical use has been found.

[0024] One type of wireless power transfer method is a wireless power transfer technology that utilizes parity-time symmetry (hereinafter referred to as "PT symmetry"). In a wireless power transfer system that utilizes PT symmetry, even if the transmission distance changes or if a positional shift occurs between the power transfer coil and the power receiving coil, the transmitted power is always kept constant as long as PT symmetry is maintained. In other words, a wireless power transfer system that utilizes PT symmetry replaces the AC power supply in conventional magnetic field resonance wireless power transfer technology with an inverter that behaves electrically in the same way as a negative resistor, that is, an inverter that behaves as a negative resistor.

[0025] This is a well-known technique, as disclosed in, for example, Patent Document 3. To explain it in more detail, an inverter that behaves as a negative resistance is an inverter whose switching frequency and voltage amplitude are not fixed in advance, has a circuit configuration in which the switching frequency is determined by the apparent resonant frequency of the wireless power feed circuit as seen from the output end of the inverter, and has a switching frequency that quickly responds to changes in the apparent resonant frequency of the wireless power feed circuit, which may change due to changes in the transmission distance or positional misalignment of the coil. Here, the wireless power feed circuit refers to a circuit that includes a power transmitting resonant circuit, a power receiving resonant circuit, and all subsequent circuits connected thereto. Furthermore, since the power transmitting resonant circuit and the power receiving resonant circuit interact with each other, the apparent resonant frequency refers to the actual resonant frequency that takes this interaction into account.

[0026] However, conventional wireless power transfer systems utilizing PT symmetry are driven at high frequencies of approximately 1 to 3 MHz, and therefore require the use of air-core coils as the power transfer coil and the power receiving coil, which necessitates large coil dimensions, thereby limiting the applications in which they can be used. Specifically, the coil dimensions in conventional wireless power transfer systems utilizing PT symmetry are approximately 60 cm in diameter (see Non-Patent Document 1). Furthermore, due to the high frequency, placing a metal object (conductive object) around the power transfer coil and the power receiving coil reduces transmission efficiency due to eddy current loss generated in the conductive object. Therefore, it was impossible to apply this technology to a rotating target.

[0027] In order to solve the problems with conventional wireless power transfer systems that utilize PT symmetry, one of the applicants of the present invention invented a wireless power transfer device that utilizes PT symmetry, which uses a low frequency of 100 kHz or less, resulting in little reduction in transmission efficiency even when metal objects are placed in the vicinity, and can maintain high transmission efficiency even when the transmission distance changes or the coil is misaligned.The device also enables the power transfer coil and power receiving coil to be made smaller, making it suitable for use in a variety of applications, and the applicant filed a patent application for this in 2021 (see Patent Document 3).

[0028] The present invention was developed by further evolving the technology of the wireless power feeder utilizing PT symmetry in the prior patent application 3, and by repeated experiments and trial and error to enable wireless power feeding even when the positions and angles of the feed coil and receive coil are further misaligned or separated. Note that, although an example in which a rotating robot arm is the power feed target is described in the embodiment of the present invention, the present invention is not limited to rotating power feed targets. Furthermore, the shape of the coil is not limited to a solenoid coil.

[0029] FIG. 1 shows the positional relationship between the coils when the center of rotation O is located at the center of the receiving coil in a rotating power supply target in a wireless power supply system using PT symmetry, and the relationship between the rotation angle θ and the magnetic coupling coefficient k ｍ1A shows the relationship between the rotational center O of the power receiving coil 21 and the axis 21L of the power supply coil 11. In a conventional robot arm, as shown in FIG. 1A, the rotational center O of the power receiving coil 21 is generally located near the center of the power receiving coil 21. Here, the state in which the axis 11L of the power supply coil 11 and the axis 21L of the power receiving coil 21, shown by the dashed dotted lines in FIG. 1A, are parallel to each other is defined as a rotational angle of 0 degrees, and the angle between the two axes is defined as a rotational angle θ (this also applies to FIG. 2A, which will be described later).

[0030] 1(a) shows the power receiving coil before rotation, and before rotation, the axis 11L of the power feeding coil 11 and the axis of the power receiving coil (the symbol and axis are not shown for the power receiving coil shown in dashed line) are parallel. The power receiving coil after being rotated by a rotation angle θ around the vicinity of the center of this power receiving coil is shown as power receiving coil 21 by solid line.

[0031] In the case of the coil arrangement shown in FIG. 1A, that is, when the rotation center O is located near the center of the receiving coil 21, the magnetic coupling coefficient k ｍ It can be seen that the magnetic coupling coefficient k ｍ When becomes 0 (zero), power supply becomes impossible even with wireless power supply using PT symmetry. Therefore, it is not possible to constantly supply power to a robot arm that can rotate 360 ​​degrees and move it. Therefore, in order to make it move in a complex manner, the magnetic coupling coefficient k ｍ It was necessary to use a multi-joint robot arm that could move within a range that did not reach 0 (zero), that is, in this case, within a range that did not reach plus or minus 90 degrees.

[0032] On the other hand, the magnetic coupling coefficient k ｍ The first example of the coil arrangement in which k does not become 0 (zero) is shown in Fig. 2. Fig. 2 shows the positional relationship between the coils when the center of rotation O is located at one of the two magnetic poles at both ends of the solenoid-type power receiving coil in the rotating power supply target in the wireless power supply system using PT symmetry according to the first embodiment of the present invention, and the relationship between the rotation angle θ and the magnetic coupling coefficient k ｍFIG.

[0033] 1(a), the broken line in Fig. 2(a) shows the power receiving coil before rotation, and before rotation, the axis 11L of the power feeding coil 11 and the axis of the power receiving coil (the symbol and axis are not shown for the power receiving coil shown in broken line) are parallel. Furthermore, the power receiving coil after being rotated by a rotation angle θ around one of the two magnetic poles at both ends of the power receiving coil 21 (magnetic pole 202 in the example shown in Fig. 2(a)) is the power receiving coil 21 shown in solid line.

[0034] That is, FIG. 2A shows the positional relationship of the coil when the center of rotation O is located at one of the two magnetic poles (201, 202) at both ends of the receiving coil 21, and FIG. 2B shows the relationship between the rotation angle θ and the magnetic coupling coefficient k in the positional relationship of the coil in FIG. 2A. ｍ Here, although the change varies slightly depending on the shape of the coil and the position of the center of rotation, as the rotation angle θ increases, the magnetic coupling coefficient k ｍ 1 and 2 have the same tendency that the magnetic coupling coefficient k decreases. However, in the case of the positional relationship of the coils as shown in FIG. 2(a), that is, when the center of rotation O is located near one of the two magnetic poles (201, 202) at both ends of the power receiving coil 21, as shown in FIG. 2(b), ｍ It is possible to eliminate the rotation angle at which θ becomes 0. In this state, by utilizing PT symmetry, it is possible to make the transmitted power constant at any rotation angle θ.

[0035] Here, we will explain existing wireless power transfer technologies again. Wireless power transfer using a magnetic field includes electromagnetic induction and magnetic resonance. Figure 3 is a graph showing the relationship between the rotation angle of two coils (a power transfer coil and a power receiving coil) used in a wireless power transfer system and the transmitted power. Figure 3(a) shows the case of the electromagnetic induction method, and Figure 3(b) shows the case of the magnetic resonance method.

[0036] In the case of the electromagnetic induction method, the magnetic coupling coefficient k ｍAs the rotation angle of the two coils decreases, the power that can be transmitted (transmission power) also decreases. Therefore, as shown in the graph in Figure 3(a), the relationship between the rotation angle of the two coils and the transmission power is such that the transmission power is greatest when the rotation angle is 0 (zero), and the transmission power decreases as the rotation angle increases.

[0037] In the case of magnetic resonance, a specific magnetic coupling coefficient k ｍ When the magnetic coupling coefficient k is a certain value, the power supply circuit and the power receiving circuit resonate and become strongly coupled. ｍ Therefore, the relationship between the rotation angle of the two coils and the transmission power is such that the transmission power is greatest at a certain rotation angle, and the transmission power decreases as the rotation angle deviates from that angle, as shown in the graph in Figure 3(b).

[0038] As such, both methods have in common the fact that the transmitted power changes as the rotation angle changes. In practical applications, it is necessary to supply a constant amount of power to the load (device) attached to the power receiving side, so it is undesirable for the transmitted power to change depending on the rotation angle. Therefore, some method of power control is required to keep the transmitted power constant.

[0039] Here, the system configuration of a wireless power supply system will be described. Fig. 4 is an explanatory diagram showing an example of a schematic configuration of a wireless power supply system, and Fig. 4(a) shows a typical system configuration when power control is performed using existing technology. Fig. 4(b) shows an example of a system configuration when PT symmetry is used (without a repeater), and Fig. 4(c) shows another example of a system configuration when PT symmetry is used (with a repeater).

[0040] When power control is performed using existing methods, the system configuration shown in Figure 4(a) is considered. This system configuration requires sensors for detecting voltage and current values ​​in the power supply circuit and power receiving circuit, wireless communication equipment for feeding back the detected values ​​on the power receiving side to the power control unit on the power supply side, and a computer for performing arithmetic processing of the detected values ​​in the power control unit. However, if the angular velocity of rotation is fast, power control cannot keep up with that speed, and it is predicted that power control will be difficult with this configuration.

[0041] One factor that reduces the response speed of power control is the time delay that occurs in the wireless communication devices and computers mentioned above. If it were possible to perform power control using a method that does not use communication devices or computers, it would be possible to improve the response speed. Therefore, in this invention, a physical law called PT symmetry is used. As mentioned above, when PT symmetry is used, the physical phenomenon is that the transmitted power is proportional to the magnetic coupling coefficient k ｍ Therefore, even if the rotation angle changes, the transmitted power remains constant, achieving the objective. This method does not require the communication equipment or computer mentioned above, so if there is no repeater, the system configuration shown in Figure 4(b) can achieve power control with a fast response speed.

[0042] Furthermore, as described in Non-Patent Document 2, PT symmetry can be preserved even when a repeater coil is placed between a power feed coil in a power feed circuit and a power receiving coil in a power receiving circuit. In practice, a capacitor is connected to the repeater coil, forming a resonant circuit. If this resonant circuit is called a repeater, a system configuration including the repeater shown in FIG. 4(c) can also be envisioned. As will be described later, this configuration is envisioned when applying wireless power transfer using PT symmetry to a multi-joint robot arm. Note that a requirement for a resonator is that the natural resonant frequency of the repeater matches the natural resonant frequencies of the power feed circuit and the power receiving circuit. Here, the natural resonant frequency refers to the resonant frequency of the resonator alone.

[0043] Next, the limit value (critical angle) of the rotation angle will be explained. The condition for preserving PT symmetry is the magnetic coupling coefficient kｍ The critical magnetic coupling coefficient k indicates the limit value (critical value) of ｍｃ As mentioned above, when PT symmetry is preserved, the magnetic coupling coefficient k ｍ Even if the position or angle of the two coils changes, the transmitted power remains constant, but the magnetic coupling coefficient k ｍ is the critical magnetic coupling coefficient k ｍｃ If the value of k is less than 0.001, the PT symmetry cannot be maintained and it becomes difficult to keep the transmitted power constant. ｍ is the critical magnetic coupling coefficient k ｍｃ If the value falls below this, the transmitted power drops significantly, making wireless power supply practically difficult.

[0044] FIG. 5 shows the magnetic coupling coefficient k when the power receiving coil shown in FIG. 1( a) is rotated around the center of the rotation. ｍ , critical magnetic coupling coefficient k ｍｃ、 5 is a graph showing the relationship between the rotation angle of the two coils (the power supply coil and the power receiving coil) shown in FIG. 1A and the transmission power and the magnetic coupling coefficient, where the horizontal axis represents the rotation angle and the vertical axis represents the transmission power and the magnetic coupling coefficient.

[0045] In the example of FIG. 5, as shown by the dashed line in the graph, the critical magnetic coupling coefficient k ｍｃ is 0.039. The critical magnetic coupling coefficient k ｍｃ is a constant that is specific to each system. On the other hand, the magnetic coupling coefficient k ｍ is a variable, and the magnetic coupling coefficient k ｍ tends to decrease as the rotation angle θ of the two coils increases. The black circles in the graph represent the experimental results of the transmitted power, and the solid line represents the magnetic coupling coefficient k ｍ The numerical calculation results are shown.

[0046] In the example shown in FIG. 5, the magnetic coupling coefficient k ｍ is the critical magnetic coupling coefficient k ｍｃ In this case, the magnetic coupling coefficient k ｍ is the critical magnetic coupling coefficient k ｍｃSince PT symmetry is maintained up to a rotation angle of 70 degrees, where the value of the magnetic coupling coefficient k is larger than θ, the transmission power is maintained at a roughly constant value (approximately 18 W in this example). After that, when the rotation angle θ exceeds 70 degrees, the magnetic coupling coefficient k ｍ is the critical magnetic coupling coefficient k ｍｃ Since the value is smaller than , the PT symmetry cannot be preserved and the transmission power drops significantly.

[0047] In practical applications, it is desirable to make the critical angle as large as possible. If PT symmetry can be maintained at any rotation angle, the transmitted power can be kept constant even when the receiving coil is rotated one full revolution (360 degrees). This makes it possible to wirelessly transfer power to a continuously rotating target.

[0048] Next, regarding a method for increasing the critical angle, the relationship between the rotation angle θ and the magnetic coupling coefficient k shown in FIGS. 1(b) and 2(b) is ｍ As shown by the dashed line in FIG. 1(b), when the arrangement of the two coils is as shown in FIG. 1(a), the critical magnetic coupling coefficient k ｍｃ If is set to 0.1, the PT symmetry can be maintained up to a rotation angle of 44 degrees. ｍｃ The critical angle when is 0.1 is 44 degrees. Note that this graph is also line-symmetric for the rotation angle in the negative direction, so PT symmetry is actually preserved within the range of ±44 degrees (88 degrees in total).

[0049] Furthermore, as shown by the dashed line in FIG. 1(b), if the critical magnetic coupling coefficient k ｍｃ If the critical angle is 0.05, the PT symmetry is maintained up to ±66 degrees (total 132 degrees). Therefore, in order to increase the critical angle, the critical magnetic coupling coefficient k ｍｃ can be made smaller.

[0050] critical magnetic coupling coefficient k ｍｃ A method for reducing the critical angle will be described later. One method for increasing the critical angle is to reduce the magnetic coupling coefficient k ｍThe aim is to keep the value of θ as large as possible. This can be achieved by adjusting the coil arrangement. This is the coil arrangement shown in FIG. 2(a). See FIG. 2(b), which is a graph showing the case where the center of rotation O is located at one of the magnetic poles (201 or 202) of the receiving coil 21.

[0051] In the case of the coil arrangement shown in FIG. 2(a), if the critical magnetic coupling coefficient k ｍｃ is 0.05 (the dashed line in FIG. 2B), the magnetic coupling coefficient k ｍ is the critical magnetic coupling coefficient k ｍｃ Since the rotation angle does not fall below ±180 degrees, it is possible to preserve PT symmetry up to ±180 degrees (a total of 360 degrees), and the receiving coil can be rotated continuously.

[0052] As described above, the critical angle can be increased by adjusting the arrangement (positional relationship) of the power supply coil 11 and the power receiving coil 21. Specifically, the critical angle is narrowest when the coil arrangement is such that the center of rotation O is located at the center of the power receiving coil 21, as shown in Fig. 1A, whereas the critical angle is widest when the center of rotation O is located at one of the magnetic poles (201 or 202) of the power receiving coil 21, as shown in Fig. 2A.

[0053] That is, as shown in FIG. 2( a), if the power supply coil 11 and the power receiving coil 21 are arranged so that the center of rotation O of the power receiving coil 21 is located near one of the two magnetic poles (201, 202) at both ends of the power receiving coil 21, the critical angle can be increased and the range of rotation angle and transmission distance in which PT symmetry can be preserved can be expanded. Therefore, when the power receiving coil 21 is rotated relative to the power supply coil 11, it becomes possible to always supply power wirelessly while preserving PT symmetry and keeping the transmission power constant.

[0054] However, the need for wireless power supply is not limited to rotating power supply targets. Therefore, even for targets other than rotating power supply targets, in order to always supply power wirelessly while preserving PT symmetry and keeping the transmission power constant, the critical magnetic coupling coefficient k ｍｃ is made as small as possible, and the magnetic coupling coefficient k ｍ is the critical magnetic coupling coefficient kｍｃ Therefore, in the present invention, in a wireless power supply system using PT symmetry, the critical magnetic coupling coefficient k ｍｃ This paper proposes a method to reduce this.

[0055] First embodiment: First, the critical magnetic coupling coefficient k ｍｃ One method for reducing the above will be described. Fig. 6 is a conceptual diagram showing the circuit configuration of a conventional wireless power feed system using a magnetic resonance method that utilizes PT symmetry, and two types of circuit examples are shown in Figs. 6(a) and 6(b). Fig. 7 is a conceptual diagram showing an example of the circuit configuration of a wireless power feed system using a magnetic resonance method that utilizes PT symmetry according to the first embodiment of the present invention.

[0056] 6 and 7, the power supply side resonator is connected to an inverter that functions as a power supply source. On the other hand, the power receiving side resonator has a load resistance R Ｌ A load of R Ｌ is the load resistance of the wireless power supply system. １ is the self-inductance of the power coil, C １ is the capacitance of the power supply capacitor, L ２ is the self-inductance of the receiving coil, C ２ represents the capacitance of the receiving capacitor. １ and ２ represent the resistance components included in the power supply side resonator and the power receiving side resonator, respectively.

[0057] The circuit example shown in Figure 6(a) is called an S-S topology because the coil and capacitor of the power supply resonant circuit are connected in series, and the coil and capacitor of the power receiving resonant circuit are also connected in series. The circuit example shown in Figure 6(b) is called an S-P topology because the coil and capacitor of the power supply resonant circuit are connected in series, and the coil and capacitor of the power receiving resonant circuit are connected in parallel. An example of wireless power transfer that preserves PT symmetry in an S-S topology is disclosed in Non-Patent Document 3, and an example of wireless power transfer that preserves PT symmetry in an S-P topology is disclosed in Non-Patent Document 4.

[0058] 7, the power receiving side resonant circuit is configured using two capacitors, and this power receiving side circuit configuration is the circuit configuration of the wireless power feeding system of the present invention. The circuit configuration shown in FIG. 7 is a configuration of the power receiving coil and 2C ２ Two capacitors with capacitances of 1000 Ω and 1000 Ω are connected in series, and a load (rectifier circuit) is connected in parallel across one of the two capacitors. Therefore, we call this topology S-SP.

[0059] In FIG. 7, the capacitance of each capacitor is set to 2C. ２ However, 2C ２ is the capacitance C of the capacitor in the circuit example shown in FIG. 6(a) and FIG. 6(b). ２ This means that the capacitance is twice as large as that of the 2C. ２ Then, the resonant frequency f of the power receiving side resonant circuit in FIGS. 6(a), 6(b) and 7 is ２ are all equal and can be expressed as equation (1), which allows for an equal comparison of the three topologies shown in FIGS. 6(a), 6(b), and 7.

[0060]

[0061] Next, the S-SP topology shown in FIG. 7 has a lower critical magnetic coupling coefficient k than the SP topology shown in FIG. 6(b).ｍｃ The critical magnetic coupling coefficient k in each of the topologies shown in FIGS. ｍｃ can be derived as the following equations (2) to (4): ｍｃ is expressed by the following equation (2).

[0062]

[0063]

[0064]

[0065] Here, Z ０ is called the characteristic impedance of the power receiving side resonant circuit. The characteristic impedance Z ０ can be expressed by the following equation (5).

[0066]

[0067] Also, Q ２ is the quality factor of the receiving resonant circuit. And the quality factor Q of this receiving resonant circuit ２ can be expressed by the following equation (6).

[0068]

[0069] In an actual system, in all topologies, that is, in all of the above equations (2), (3), and (4), the first term (1 / Q ２ ) can be set to a value sufficiently smaller than the second term, so the critical magnetic coupling coefficient k ｍｃ The second term is the dominant term for determining

[0070] Comparing the second term of the SP topology (equation (3)) and the S-SP topology (equation (4)), we can see that the second term of the S-SP topology is one-fourth the value. Therefore, by using the S-SP topology, the critical magnetic coupling coefficient k ｍｃSince the value of can be reduced to about one-fourth, the allowable range of the rotation angle of the coil can be widened.

[0071] In FIG. 7, the capacitance of each of the two capacitors is set to 2C. ２ However, it is not necessary to set them to the same value, as the critical magnetic coupling coefficient k ｍｃ The capacitance condition of the two capacitors is that the combined capacitance of these two capacitors is C ２０ When this is the case, the following equation (7) is satisfied.

[0072]

[0073] In this way, if the circuit configuration is an S-SP topology as shown in FIG. 7, that is, if the resonant circuit configuration in the power receiving circuit is such that the power receiving coil and two capacitors are connected in series and a rectifier circuit is connected across either one of the two capacitors, the critical magnetic coupling coefficient k that can preserve PT symmetry can be ｍｃ By reducing the value of , it is possible to further expand the range of rotation angle and transmission distance in which PT symmetry can be preserved. Therefore, when the receiving coil is rotated relative to the feeding coil, it is possible to always feed wirelessly with PT symmetry preserved and the transmission power kept constant.

[0074] This means that in the rectifier circuit, the diode is reverse biased, so it has capacitance, but this capacitance has nonlinear characteristics with respect to the reverse bias voltage, and acts so that the capacitance changes with the voltage. As a result, when the rectifier circuit is connected, the resonant frequency also changes. As a result, the output voltage of the receiving resonant circuit can be stabilized. However, with the S-SP topology circuit configuration shown in Figure 7, it can be assumed that the capacitance component of the rectifier circuit does not affect the resonant frequency of the receiving resonant circuit.

[0075] 8 is a conceptual diagram showing another example of the circuit configuration of a wireless power transfer system using magnetic resonance technology that utilizes PT symmetry according to the first embodiment of the present invention. Specifically, these are modifications of the S-SP topology of FIG. 7, with FIG. 8(a) being an S-SP / SP topology and FIG. 8(b) being an S-SP / SP / SP topology. These also have a circuit configuration in which the resonant circuit in the power receiving circuit directly connects the power receiving coil to two capacitors, and a rectifier circuit is connected across either one of the two capacitors.

[0076] First, the S-SP / SP topology shown in FIG. 8(a) also has a lower critical magnetic coupling coefficient k ｍｃ The critical magnetic coupling coefficient k in the case of the S-SP / SP topology in FIG. ｍｃ The formula is expressed as the following formula (8).

[0077]

[0078] Thus, compared with the SP topology shown in FIG. 6(b), the S-SP / SP topology shown in FIG. 8(a) has a critical magnetic coupling coefficient k ｍｃ The capacitance of the four capacitors does not necessarily have to be as shown in FIG. 8(a), but the critical magnetic coupling coefficient k ｍｃ The effect of reducing the capacitance of the capacitor is expected. ２ The combined capacitance of the four capacitors as seen from both ends of the ４０ When this is the case, the following equation (9) is satisfied.

[0079]

[0080] Furthermore, as a circuit obtained by further modifying FIG. 8(a), the critical magnetic coupling coefficient k ｍｃThe S-SP / SP topology shown in Figure 8(a) is a two-stage ladder circuit, whereas the S-SP / SP / SP topology shown in Figure 8(b) is a three-stage ladder circuit. In principle, it is also possible to increase the number of stages in the ladder circuit to n. In this case, the condition for the capacitance of the capacitor is ２ ) is the combined capacitance of 2n pieces seen from both ends of ２ｎ０ When this is the case, the following equation (10) is satisfied.

[0081]

[0082] As described above, in the circuit configuration shown in FIG. 7 or 8(a) and (b), that is, in the configuration of the resonant circuit in the power receiving circuit in wireless power transfer utilizing PT symmetry, by configuring the circuit in such a way that the power receiving coil and two capacitors are connected in series and a rectifier circuit is connected across either one of the two capacitors, the critical magnetic coupling coefficient k ｍｃ By reducing the value of , it is possible to expand the range of rotation angle and transmission distance in which PT symmetry can be preserved. This eliminates the need for adjustment or control of the positions and angles of the power supply coil and power receiving coil, and the structure is simple. High transmission efficiency can be maintained without interruption even if the positions and angles of the power supply coil and power receiving coil are slightly misaligned or separated. Therefore, it is possible to constantly supply power wirelessly while preserving PT symmetry and maintaining a constant transmission power, with as few restrictions as possible on the positional relationship between the two coils and with even more leeway than before.

[0083] If the load to be powered wirelessly is a simple pure resistor for the purpose of generating heat, AC drive is possible and rectification is not required. Therefore, when using a pure resistive load, instead of connecting a rectifier circuit across a single capacitor, it is also possible to connect a pure resistor as a load directly across a single capacitor.

[0084] Second Embodiment As in the first embodiment, the critical magnetic coupling coefficient k ｍｃAs can be seen from the second term of the above equations (3) and (4), in the SP topology and S-SP topology, the load resistance R Ｌ If the value of is large, the critical magnetic coupling coefficient k ｍｃ However, in actual applications, the value of the load resistance cannot be freely selected. For example, if the load has a voltage of 10 V and a power of 20 W, the load resistance R Ｌ Therefore, it is difficult to adjust the load resistance to a convenient value.

[0085] As a method for solving this problem, we propose a circuit configuration of a power receiving circuit shown in Fig. 9. Fig. 9 is a circuit configuration diagram showing an example of a power receiving circuit in a wireless power feeding system of a magnetic field resonance type using PT symmetry in embodiment 2 of the present invention. In this circuit example shown in Fig. 9, a rectifier circuit is connected to the rear stage of a power receiving side resonator of an S-SP topology, followed by a step-down converter (a type of DC-DC converter, a DC-DC converter whose output voltage is lower than the input voltage is called a "step-down converter") and a load. If there were no rectifier circuit or step-down converter, the critical magnetic coupling coefficient k ｍｃ follows the above-mentioned formula (4). However, by connecting the rectifier circuit and the step-down converter, formula (4) can be rewritten as the following formula (11).

[0086]

[0087] Here, R ｅｆｆ is called the AC equivalent load resistance. In reality, the load resistance R Ｌ However, if a load resistor is connected directly to the AC circuit (receiving-side resonant circuit) without going through a rectifier circuit or a DC-DC converter, the resistance value of the latter must be equal to the AC equivalent load resistance R ｅｆｆ That is, the AC equivalent load resistance R ｅｆｆ is the equivalent resistance value connected to the receiving side resonant circuit, and the load resistance R Ｌ The AC equivalent load resistance R ｅｆｆHow the value of is determined will be explained next.

[0088] More specifically, Figure 9 shows details of the power receiving circuit in a system configuration without a repeater that utilizes the PT symmetry shown in Figure 4(b), in which a full-wave rectifier circuit is used as the rectifier circuit and a step-down chopper circuit is used as the DCDC converter.

[0089] As is well known, a step-down chopper circuit periodically turns on / off a semiconductor switching device such as an FET (the state where the drain-source is conducting is called ON, and the state where the drain-source is not conducting is called OFF), thereby periodically creating a state where current flows and does not flow between the drain and source. The time during which current flows in one period is called T ＯＮ , the time that is not flowing is T ＯＦＦ Then, the conduction rate D, which indicates the proportion of time that current is flowing, can be expressed by the following equation (12).

[0090]

[0091] It is well known that the duty ratio D and the output voltage of a step-down chopper circuit are proportional to each other, and it is also well known that the output voltage can be stably controlled by automatically adjusting (automatically controlling) the duty ratio D. However, in the present invention, this duty ratio D is calculated by the critical magnetic coupling coefficient k ｍｃ It is also used to reduce the AC equivalent load resistance R ｅｆｆ can be expressed as the following equation (13).

[0092]

[0093] AC equivalent load resistance R ｅｆｆ is the load resistance R Ｌ The square of the conductance D ２ The coefficient 0.62 in equation (13) is not a universal value and may vary depending on the circuit configuration, etc., but it can be determined in advance using a circuit simulator, etc. This coefficient will be called the resistance conversion coefficient.

[0094] For example, if the conduction ratio D is 0.25 and the load resistance R Ｌ is 10 ohms, the AC equivalent load resistance R ｅｆｆ is 100 ohms. In other words, the AC equivalent load resistance R ｅｆｆ can be increased by approximately 10 times. ｅｆｆ becomes larger, the critical magnetic coupling coefficient k ｍｃ is known to be smaller.

[0095] That is, in the configuration of the resonant circuit in the power receiving circuit, a rectifier circuit is connected to the resonant circuit, and a step-down chopper type DC-DC converter is provided in the subsequent stage of the rectifier circuit. The value of the duty factor D of this DC-DC converter determines the AC equivalent load resistance R connected to the resonant circuit in the power receiving circuit. ｅｆｆ If the circuit configuration is such that the value of is adjusted, the critical magnetic coupling coefficient k ｍｃ By reducing the value of , it is possible to widen the range of rotation angle and transmission distance in which PT symmetry can be preserved. Therefore, when the receiving coil is rotated relative to the feeding coil, it is possible to always feed power wirelessly while preserving PT symmetry and keeping the transmission power constant.

[0096] In the power receiving circuit shown in Figure 9, a choke coil must be provided before the smoothing capacitor of the full-wave rectifier circuit. The role of a choke coil in a typical rectifier circuit is to remove pulsating currents superimposed on the output DC current, but the role of the choke coil in embodiment 2 of the present invention is completely different. This role will be explained below.

[0097] As described above, from equation (11), the critical magnetic coupling coefficient k ｍｃ In order to reduce the ｅｆｆ Furthermore, from equation (13), the AC equivalent load resistance R ｅｆｆ In other words, if this value becomes small, the AC equivalent load resistance R ｅｆｆ also becomes a small value, and as a result, the critical magnetic coupling coefficient k ｍｃIt becomes impossible to reduce the resistance. Choke coils prevent this. The mechanism behind this is explained below using the results of analysis using a circuit simulator.

[0098] For ease of explanation, only the full-wave rectifier circuit will be considered. Figure 10 shows a simulation circuit for comparatively verifying the effect of the choke coil in embodiment 2 of the present invention, with Figure 10(a) showing the circuit without a choke coil and Figure 10(b) showing the circuit with a choke coil.

[0099] The inductance of the choke was set to 18 μH, the same as the actual device. A sinusoidal AC voltage Vi with an amplitude of 64 V and a frequency of 48 kHz, equivalent to the actual device, was input to the input. A resistance of 148 ohms was connected to the output terminal as a resistance component equivalent to the actual device. This resistance will be called the output resistance. The input resistance seen from the input terminal is the value obtained by dividing the input voltage Vi by the input current Ii. This input resistance R ｅｆｆ If the input resistance is 59 ohms, the output resistance is 148 ohms, so the ratio is 0.40 (= 59 / 148). This value corresponds to the resistance conversion coefficient in equation (13).

[0100] Figure 11 shows the change over time (waveform) of the input voltage Vi and the input current Ii, for the purpose of comparatively verifying the effect of the choke coil in embodiment 2 of the present invention, where Figure 11(a) shows the waveform when there is no choke coil and Figure 11(b) shows the waveform when there is a choke coil.

[0101] As can be seen from Figure 11(a), when there is no choke coil, the waveform of the input current Ii is a sharp, spike-like waveform. This is due to the charging current rushing into the smoothing capacitor. On the other hand, when looking at the waveform of the circuit with a choke coil shown in Figure 11(b), the waveform of the input current Ii loses its sharpness and becomes a smoother waveform compared to when there is no choke coil. This is because the choke coil has the effect of suppressing inrush current.

[0102] Regardless of whether a choke coil is used or not, if the input resistance is calculated by dividing the average value of the input voltage Vi and the average value of the input current Ii averaged over one period, the result is 182 ohms, which is the same for both. However, the input resistance calculated from the average value over one period is R ｅｆｆ It cannot be said that the original input resistance R ｅｆｆ is the input resistance value when energy is moving from the receiving-side resonant circuit to the full-wave rectifier circuit. (Input resistance R ｅｆｆ is the critical magnetic coupling coefficient k of PT symmetry ｍｃ It should be noted that this is the input resistance value when calculating the resistance, and is different from the definition of input resistance in general circuit theory.)

[0103] As can be clearly seen from the waveform of the input current Ii in Figure 11(a), the time interval during which the charging current flows into the smoothing capacitor is a very short interval within one cycle. In other time intervals, the current flowing from the receiving-side resonant circuit to the full-wave rectifier circuit is completely "zero". This is because the input current Ii does not flow unless the input voltage Vi exceeds the charging voltage of the smoothing capacitor. Therefore, in the time interval during which the input current Ii does not flow, even if the input voltage Vi is a finite value, no energy is transferred from the receiving-side resonant circuit to the full-wave rectifier circuit. Therefore, the value obtained by dividing the average value of the input voltage Vi by the average value of the input current Ii during the time interval during which current is flowing from the waveform of the input current Ii to calculate the input resistance is the original input resistance R. ｅｆｆ is.

[0104] When there is no choke coil (as in FIG. 11(a)), the waveform of the input current Ii becomes narrow and sharp, and the current value also becomes large. ｅｆｆ becomes smaller. In this simulation, it was 17.5 ohms. Therefore, the resistance conversion factor is 0.12 (= 17.5 / 148).

[0105] Furthermore, when a choke coil is present (as in FIG. 11(b)), the waveform of the input current Ii becomes wide and smooth, and the current value also becomes small, so the input resistance R ｅｆｆIn this simulation, the resistance was 91.0 ohms. Therefore, the resistance conversion factor is 0.61 (=91.0 / 148).

[0106] From the above, the choke coil has the effect of increasing the resistance conversion coefficient, and as a result, the critical magnetic coupling coefficient k ｍｃ It was possible to achieve this. In this circuit example, a simple circuit using one choke coil was shown and explained for ease of explanation, but it is also possible to use a different circuit configuration. Specifically, a similar effect can be expected even with a circuit that smooths the waveform of the input current Ii by adding a diode and a compensation capacitor, as proposed in Non-Patent Document 5.

[0107] In other words, if the resonant circuit within the receiving circuit is configured such that a rectifier circuit is connected to the resonant circuit and a choke coil is provided in the rectifier circuit between the rectifier diode and the smoothing capacitor, the distortion of the current waveform flowing from the receiving resonant circuit to the rectifier circuit can be reduced, and the deterioration of the range of rotation angle and transmission distance in which PT symmetry can be maintained due to the generation of harmonics caused by current distortion can be prevented, making it possible to always supply power wirelessly while maintaining PT symmetry and keeping the transmission power constant.

[0108] As described above, in the circuit configuration shown in FIG. 10(b), that is, in the configuration of the resonant circuit in the power receiving circuit in wireless power transfer utilizing PT symmetry, a rectifier circuit is connected to the resonant circuit, and a choke coil is provided between the rectifier diode and the smoothing capacitor in the rectifier circuit, the critical magnetic coupling coefficient k ｍｃBy reducing the value of , distortion in the current waveform flowing from the receiver-side resonant circuit to the rectifier circuit is reduced, and deterioration of the rotation angle and transmission distance range in which PT symmetry can be maintained due to the generation of harmonics caused by current distortion can be prevented. This eliminates the need for adjustment or control of the positions and angles of the power supply coil and receiver coil, and the structure is simple. High transmission efficiency can be maintained without interruption even if the positions and angles of the power supply coil and receiver coil are slightly misaligned or separated. Therefore, it is possible to constantly supply power wirelessly while maintaining constant transmission power and preserving PT symmetry, with as few restrictions as possible on the positional relationship between the two coils and with even more leeway than before.

[0109] Here, the role of the choke coil in this second embodiment is to smooth the waveform of the input current Ii. A similar effect can be obtained with a power factor correction circuit called a PFC (Power Factor Correction) circuit. A power factor of 1 occurs when both the voltage and current are sinusoidal waves, which is the most desirable state. Therefore, in the power receiving circuit shown in FIG. 12, the parameters of the choke coil and PFC circuit are adjusted to obtain the critical magnetic coupling coefficient k ｍｃ An experiment was conducted to investigate the relationship between

[0110] FIG. 12 is a circuit diagram showing another example of a power receiving circuit of a wireless power transfer system using magnetic resonance technology and utilizing PT symmetry according to the second embodiment of the present invention. FIG. 13 is a table showing experimental results showing the relationship between the power factor and whether or not the coil can be rotated in the power receiving circuit shown in FIG. 12 . As shown in FIG. 13 , when the power factor was 0.5, there was an angle at which power could not be supplied when the coil was rotated 360 degrees (±180 degrees). Furthermore, when the power factor was 0.6, power could be supplied even when the coil was rotated 360 degrees (±180 degrees), although this was sometimes unstable. Furthermore, although it goes without saying that a power factor closer to 1.0 is better, in this experiment, stable power could be supplied even when the coil was rotated 360 degrees (±180 degrees) when the power factor was 0.7, 0.8, 0.9, or 0.95.

[0111] In other words, we were able to obtain the result that the efficiency of wireless power transmission is sufficient if the power factor is adjusted to be between 0.6 and 1.0. As a result, the same effect can be obtained even if the power receiving circuit shown in Figure 12 is used instead of the power receiving circuit shown in Figure 10(b).

[0112] As described above, in the circuit configurations shown in FIG. 10(b) and FIG. 12, that is, in the configuration of the resonant circuit in the power receiving circuit in wireless power transfer utilizing PT symmetry, a rectifier circuit is connected to the resonant circuit, and in the rectifier circuit, a power factor improvement circuit such as a choke coil or PFC circuit is provided between the rectifier diode and the smoothing capacitor, and the power factor of the power factor improvement circuit is adjusted to be between 0.6 and 1.0, by using a configuration in which the critical magnetic coupling coefficient k ｍｃ By reducing the value of , distortion in the current waveform flowing from the receiver-side resonant circuit to the rectifier circuit is reduced, and deterioration of the rotation angle and transmission distance range in which PT symmetry can be maintained due to the generation of harmonics caused by current distortion can be prevented. This eliminates the need for adjustment or control of the positions and angles of the power supply coil and receiver coil, and the structure is simple. High transmission efficiency can be maintained without interruption even if the positions and angles of the power supply coil and receiver coil are slightly misaligned or separated. Therefore, it is possible to constantly supply power wirelessly while maintaining constant transmission power and preserving PT symmetry, with as few restrictions as possible on the positional relationship between the two coils and with even more leeway than before.

[0113] Embodiment 3. As in the above-described embodiments 1 and 2, the critical magnetic coupling coefficient k ｍｃ Here, we will explain another method for reducing the critical magnetic coupling coefficient k by using an actual system configuration without a repeater that utilizes PT symmetry as shown in Figure 4(b). ｍｃ The results of experiments conducted to determine whether it is possible to reduce the value of are described below with reference to FIGS.

[0114] First, the purpose of this experiment will be explained. Figure 14 shows the relationship between the transmission distance between two coils (a power supply coil and a power receiving coil) and the magnetic coupling coefficient k ｍ 14 is a graph showing the relationship between the magnetic coupling coefficient k and the magnetic coupling coefficient k. The circles in FIG. 14 show the experimental results, and the solid line shows the results of numerical calculations. It can be seen that the experimental results and the results of numerical calculations are almost the same. Here, the transmission distance refers to the length of the gap between the power supply coil and the power receiving coil when the rotation angle of the two coils (power supply coil and power receiving coil) is 0 degrees. As the transmission distance increases, the magnetic coupling coefficient k ｍ tends to decrease.

[0115] According to FIG. 14, for example, the critical magnetic coupling coefficient k ｍｃ If k is 0.1, the limit of the transmission distance that can maintain PT symmetry is 45 mm (see the dashed line in FIG. 14). This limit distance is called the critical distance. If the critical magnetic coupling coefficient k ｍｃ It can be easily seen from the graph shown in FIG. 14 that if the critical magnetic coupling coefficient k is 0.04, the critical distance is 76 mm (see the dashed line in FIG. 14). ｍｃ The smaller is the longer the critical distance.

[0116] Fig. 15 is a graph showing experimental results showing the relationship between the transmission distance and the transmission power between two coils (a power supply coil and a power receiving coil). Fig. 15(a) shows the experimental results of investigating the relationship between the transmission distance and the transmission power between two coils (a power supply coil and a power receiving coil) for each of the four conditions of the duty ratio D = 0.22, 0.25, 0.31, and 0.37. When PT symmetry can no longer be maintained, the transmission power cannot be maintained constant, and the transmission power drops sharply. The distance at which this drop begins corresponds to the critical distance. That is, when the conduction ratio D = 0.37 (X mark in Figure 15(a)), the critical distance is 57 mm, when the conduction ratio D = 0.31 (□ mark in Figure 15(a)), the critical distance is 67 mm, when the conduction ratio D = 0.25 (△ mark in Figure 15(a)), the critical distance is 77 mm, and when the conduction ratio D = 0.21 (○ mark in Figure 15(a)), the critical distance is 84 mm.

[0117] As shown in Fig. 15(a), the experimental results confirm that the critical distance is extended by reducing the conduction ratio D, as intended. The critical distance for each measured conduction ratio D is calculated by the above-mentioned formula (11) and the transmission distance and magnetic coupling coefficient k shown in Fig. 14. ｍ It was also confirmed that the calculated critical distance was in good agreement with the numerical calculation results.

[0118] Furthermore, Figure 15(b) shows the results of an experiment investigating the relationship between the transmission distance and transmission power between two coils (a power supply coil and a power receiving coil) for an S-P topology circuit (Figure 6(b)) and an S-SP topology circuit (Figure 7). When PT symmetry can no longer be maintained, the transmission power cannot be maintained constant, and the transmission power drops sharply. The distance at which this drop begins corresponds to the critical distance. That is, the critical distance for the S-P topology circuit (marked with an x ​​in Figure 15(b)) is 37 mm, and the critical distance for the S-P topology circuit (marked with a ● in Figure 15(b)) is 77 mm.

[0119] As a result, when the SP topology circuit (FIG. 6(b)) is changed to the S-SP topology circuit (FIG. 7), the critical magnetic coupling coefficient k ｍｃ It was confirmed that the critical magnetic coupling coefficient k ｍｃ The smaller the critical angle, the wider the critical magnetic coupling coefficient k ｍｃ is inversely proportional to the critical distance, so by comparing the critical distances of the SP topology and the S-SP topology, the critical magnetic coupling coefficient k ｍｃ The difference can be seen, albeit indirectly.

[0120] 15(b), we can see that the critical distance is significantly improved by changing from the SP topology to the S-SP topology. In other words, these experiments show that the theoretically predicted effects were achieved, along with the improvements due to the S-SP topology and the conductance D.

[0121] As mentioned above, the step-down chopper circuit stabilizes the output voltage by automatically adjusting (automatically controlling) the duty ratio D, and so in this proposed system, the output voltage is also stabilized by automatically adjusting the duty ratio D. However, if the duty ratio D changes during operation, the critical magnetic coupling coefficient k ｍｃ This is undesirable because it leads to a sudden break in PT symmetry during operation and a significant drop in transmitted power.

[0122] To solve this problem, we propose a method of setting an upper limit for the duty ratio D. For example, if the upper limit for the duty ratio D in a step-down chopper circuit is set to 0.3 and the output voltage is controlled within the duty ratio D range of 0 to 0.3, the critical magnetic coupling coefficient k ｍｃ Since the upper limit of the critical angle and critical distance is determined, the critical angle and critical distance will not be smaller than the assumed critical angle and critical distance.

[0123] As a final confirmation of the correctness of this theory, an experiment was conducted to see whether the method proposed in this invention can keep the transmitted power constant even when the coil is rotated ±180 degrees (total 360 degrees). As mentioned above, using an actual device with a repeater-less system configuration using PT symmetry as shown in Figure 4(b), the receiving-side resonant circuit was set to S-SP topology, the duty factor D of the step-down chopper circuit was set to 0.26, and the load resistance R Ｌ In this case, the critical magnetic coupling coefficient k calculated from equation (11) is ｍｃ The value was 0.039.

[0124] Furthermore, the coil was arranged so that one of the magnetic poles of the receiving coil was the center of rotation, as shown in Figure 2(a). The transmission distance was fixed at 30 mm. Under these conditions, theoretically, the magnetic coupling coefficient k ｍ is the critical magnetic coupling coefficient k ｍｃ Since the value will not fall below (=0.039), it can be predicted that the objective will be achieved.

[0125] 16 is a graph showing experimental results of the relationship between the rotation angle of two coils (a power supply coil and a power receiving coil) and the transmitted power. Fig. 16 shows the relationship between the magnetic coupling coefficient k and the rotation angle when the power receiving coil is rotated around one of the two magnetic poles at both ends of the coil shown in Fig. 2(a). ｍ , critical magnetic coupling coefficient k ｍｃ、 10 is a graph showing experimental results showing the relationship between the frequency and the transmission power.

[0126] 16 is a graph showing the relationship between the rotation angle of the two coils (the power supply coil and the power receiving coil) shown in FIG. 2A and the transmission power and the magnetic coupling coefficient, where the horizontal axis represents the rotation angle and the vertical axis represents the transmission power and the magnetic coupling coefficient. The dashed line in the graph represents the critical magnetic coupling coefficient k ｍｃ 16 shows the experimental results for the transmission power (=0.039), the black circles indicate the experimental results for the transmission power, and the solid line indicates the numerical calculation results for the magnetic coupling coefficient. Note that this Figure 16 shows the experimental results when all of the first, second, and third embodiments are implemented.

[0127] As shown in Figure 16, the experimental results confirmed that the transmission power was kept almost constant over a rotation angle of ±180 degrees (a total of 360 degrees). ｍ is the critical magnetic coupling coefficient k ｍｃ (=0.039), and it was confirmed that the PT symmetry was maintained over 360 degrees, resulting in a constant transmitted power. Furthermore, it was confirmed that the transmitted power remained constant even when the coil was rotated continuously for more than one revolution.

[0128] In this way, it was confirmed not only through theoretical considerations but also through experiments that the present invention is effective and has great advantages.

[0129] As described above, in the configuration of the resonant circuit in the power receiving circuit, a rectifier circuit is connected to the resonant circuit, and a step-down chopper type DCDC converter is provided in the subsequent stage of the rectifier circuit. By configuring the circuit in this way, the value of the AC equivalent load resistance connected to the resonant circuit in the power receiving circuit is adjusted depending on the value of the duty factor D of this DCDC converter. By using this circuit configuration, it is possible to maintain the PT symmetry by adjusting the critical magnetic coupling coefficient kｍｃ This eliminates the need to adjust or control the positions and angles of the power supply coil and power receiving coil, simplifies the structure, and maintains high transmission efficiency without interruption even if the positions and angles of the power supply coil and power receiving coil are slightly misaligned or separated. This makes it possible to constantly supply power wirelessly while preserving PT symmetry and keeping the transmission power constant, with as few restrictions as possible on the positional relationship between the two coils and with even more leeway than before.

[0130] 17A and 17B are schematic perspective views and internal see-through views showing an example in which the wireless power supply systems according to the first to third embodiments of the present invention are applied to a motor. Fig. 17A is a perspective view of the exterior of the motor viewed diagonally from above, and Fig. 17B is an internal see-through view obtained by seeing through Fig. 17A to show the interior. The upper part (upper half) of the motor shown in Figs. 17A and 17B is the wireless power supply unit, and the lower part (lower half) is the motor, and the outer coil visible in Fig. 17A is the power supply coil 11. Fig. 17B shows the state before rotation.

[0131] As shown in Fig. 17(b), a coil (power receiving coil 21) is also arranged on the inside of the wireless power feeder, and this inner power receiving coil 21 rotates with the rotation of the motor, causing its position to fluctuate (see Figs. 17(c) and 17(d)). Fig. 17(c) shows a state in which the motor has rotated slightly, causing the inner coil, power receiving coil 21, to rotate slightly and become misaligned with respect to the outer coil, power feeding coil 11. Fig. 17(d) shows a state in which the motor has rotated even more than in Fig. 17(c), causing the inner coil, power receiving coil 21, to rotate even further and become misaligned with respect to the outer coil, power feeding coil 11.

[0132] 17 , the power receiving coil 21 rotates together with the motor, so the positional relationship between the power feeding coil 11 and the power receiving coil 21 is constantly changing, with the distance between the two coils getting closer and farther apart. However, even in such a case, by using a wireless power feeding system that utilizes PT symmetry and has the characteristics described in the first to third embodiments of the present invention, the power fed from the outer power feeding coil 11 can be kept constant.

[0133] It should be noted that within the scope of the present invention, the embodiments may be freely combined, or any component of each embodiment may be modified, or any component of each embodiment may be omitted.

[0134] The wireless power supply system of the present invention can be applied to various devices to which power needs to be supplied wirelessly, such as artificial organs, factory equipment, etc. It can also be applied to various power supply targets that rotate, such as robot arms and motors.

[0135] 11 Power supply coil 11L Axis of power supply coil 11 21 Power receiving coil 21L Axis of power receiving coil 21 201, 202 Magnetic pole

Claims

1. A wireless power supply system that utilizes Parity-Time symmetry (hereinafter referred to as "PT symmetry"), comprising a power supply circuit provided with a power supply coil, and a power receiving circuit provided with a power receiving coil, the power supply circuit and the power receiving circuit each having a resonant circuit, and as a means for always wirelessly supplying power while preserving the PT symmetry and keeping the transmitted power constant, the resonant circuit in the power receiving circuit is configured so that the power receiving coil and two capacitors are connected in series, and a rectifier circuit is connected to both ends of one of the two capacitors.

2. A wireless power supply system that utilizes parity-time symmetry (hereinafter referred to as "PT symmetry"), comprising a power supply circuit provided with a power supply coil, and a power receiving circuit provided with a power receiving coil, and the power supply circuit and the power receiving circuit each have a resonant circuit, and as a means for always wirelessly supplying power while preserving the PT symmetry and keeping the transmission power constant, the resonant circuit in the power receiving circuit is configured so that a rectifier circuit is connected to the resonant circuit, and in the rectifier circuit, a power factor correction circuit is provided between a rectifier diode and a smoothing capacitor, and the power factor of the power factor correction circuit is adjusted to be between 0.6 and 1.

0.

3. A wireless power supply system that utilizes parity-time symmetry (hereinafter referred to as "PT symmetry"), comprising a power supply circuit provided with a power supply coil, and a power receiving circuit provided with a power receiving coil, and the power supply circuit and the power receiving circuit each have a resonant circuit, and as a means for always wirelessly supplying power while preserving the PT symmetry and keeping the transmission power constant, the resonant circuit in the power receiving circuit is configured so that a rectifier circuit is connected to the resonant circuit and a step-down chopper type DC-DC converter is provided in the subsequent stage of the rectifier circuit, and the value of the AC equivalent load resistance connected to the resonant circuit in the power receiving circuit is adjusted depending on the value of the duty factor D of this DCDC converter.

Images