Power transmission circuit, power transmission device, and contactless power supply system

Abstract

To suppress an increase of a leakage electromagnetic field in a non-contact power supply system.SOLUTION: A power transmission circuit 120-120O for supplying power to a power reception device 200 in a non-contact manner comprises: a first resonance circuit 10 including a first coil Ls1 connected to a power supply device 110, which supplies AC power in a predetermined operation frequency, and a first impedance variable element 20 connected in series with the first coil between the first coil and the power supply device for switching a state of the first resonance circuit between a resonant state and a non-resonant state; and a second resonance circuit 12 including a second coil Ls2 magnetically coupled with the first coil and a second impedance variable element 22 connected in parallel with the second coil for switching a state of the second resonance circuit between a resonant state and a non-resonant state. Any one of both ends of the second coil is connected to the power supply device.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a power transmission circuit, a power transmission device, a power reception device, and a non-contact power supply system.

Background Art

[0002] A non-contact power supply system that supplies power to an electric vehicle equipped with a power reception device in a non-contact manner from a power transmission device is known. The non-contact power supply system described in Patent Document 1 improves power supply efficiency by providing a tertiary coil that magnetically couples to a primary coil of the power transmission device and a secondary coil of the power reception device, respectively.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in order to magnetically couple each of the primary coil and the secondary coil, when the primary coil and the tertiary coil are arranged close to each other, a stray capacitance is generated between the coils, resulting in a leakage current in the tertiary coil and an increase in the leakage electromagnetic field caused by the tertiary coil.

Means for Solving the Problems

[0005] The present disclosure can be realized in the following forms.

[0006] According to one embodiment of the present disclosure, a power transmission circuit (120 to 120O) for non-contact power supply to a power receiving device (200) is provided. This power transmission circuit includes a first resonance circuit (10) having a first coil (Ls1) connected to a power supply device (110) that supplies AC power at a predetermined operating frequency, and a first impedance variable element (20) connected in series with the first coil between the first coil and the power supply device for switching the state of the first resonance circuit between a resonance state and a non-resonance state; and a second resonance circuit (12) having a second coil (Ls2) magnetically coupled to the first coil, and a second impedance variable element (22) connected in parallel with the second coil for switching the state of the second resonance circuit between a resonance state and a non-resonance state. The second coil has one of its both ends connected to the power supply device.

[0007] According to the power transmission circuit of this embodiment, since one of the both ends of the second coil is connected to the power supply device, by flowing the leakage current flowing through the second coil through the power line via the capacitance generated between the first coil and the second coil, it is possible to shorten the current path of the leakage current flowing through the second coil and / or make the potentials of the first coil and the second coil the same. Thereby, the leakage current flowing through the second coil can be suppressed, and an increase in the leakage electromagnetic field caused by the leakage current can be suppressed.

Brief Description of the Drawings

[0008]

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Embodiments for Carrying out the Invention

[0009] A. First Embodiment: A-1. Device Configuration: The contactless power supply system 1000 of this embodiment shown in FIG. 1 includes a power transmission device 100 and a power reception device 200. In this embodiment, the power transmission device 100 is buried under the road surface 105. The power reception device 200 is mounted on an electric vehicle 202 as a moving body traveling on the road surface 105. In this embodiment, the electric vehicle 202 is configured as an AGV (Automatic Guided Vehicle) traveling inside a factory or a warehouse. Note that the electric vehicle 202 may be configured as an electric vehicle or a hybrid vehicle.

[0010] In the contactless power supply system 1000, when the electric vehicle 202 travels on the road surface 105, the power transmission device 100 supplies power to the power reception device 200. "Traveling on the road surface 105" includes not only the case where the electric vehicle 202 is moving but also the case where the electric vehicle 202 is stopped near fixed equipment such as a transfer robot or a conveyor for loading and unloading of conveyed goods. In FIG. 1, the x-axis direction indicates the traveling direction of the electric vehicle 202, the y-axis direction indicates the width direction of the electric vehicle 202, and the z-axis direction indicates the vertically upward direction.

[0011] The power transmission device 100 includes a power supply device 110 and a plurality of power transmission circuits 120. The power supply device 110 outputs AC power at a predetermined operating frequency. As shown in FIG. 2, the power supply device 110 includes a utility power supply PS, a noise filter 111, a PFC (Power Factor Correction) circuit 112, an inverter 113, and a high-frequency filter 114. In this embodiment, the noise filter 111, the PFC circuit 112, the inverter 113, and the high-frequency filter 114 are connected to the utility power supply PS as a set. However, two or more sets may be connected in parallel to the utility power supply PS.

[0012] The noise filter 111 removes the noise of the AC power supplied from the utility power supply PS. The PFC circuit 112 is a well-known circuit that eliminates the phase difference between the input voltage and the output current generated by the noise removal in the noise filter 111, suppresses harmonics, and improves the power factor to approach 1. The AC power supplied from the utility power supply PS is converted into DC power and smoothed by the noise filter 111 and the PFC circuit 112. The inverter 113 converts the supplied DC power into high-frequency AC power. The high-frequency filter 114 extracts and passes the AC power at a predetermined operating frequency from the supplied high-frequency AC power. The AC power that has passed through the high-frequency filter 114 is supplied to each power transmission circuit 120.

[0013] As shown in FIG. 1, the plurality of power transmission circuits 120 are installed along the x-axis direction in the ground of the runway 105. Note that a part of the plurality of power transmission circuits 120 may be installed at a location other than the ground of the runway 105, for example, on the side of fixed equipment such as a multi-joint robot for transportation or a conveyor. Each power transmission circuit 120 is connected to the power supply device 110 in parallel with each other and supplied with AC power from the power supply device 110. Each power transmission circuit 120 has a primary resonance circuit 10. The primary resonance circuit 10 is supplied with AC power from the power supply device 110 and transmits AC power to the secondary resonance circuit 240 described later in a non-contact manner. The specific configuration of the power transmission circuit 120 including the primary resonance circuit 10 will be described later.

[0014] The power receiving device 200 includes a battery 210, an auxiliary battery 215, a power receiving side control unit 220, a power receiving circuit 230, a secondary resonance circuit 240, a DC / DC converter circuit 260, an inverter circuit 270, a motor generator 280, and an auxiliary machine 290. Note that the power receiving device 200 may not include the auxiliary machine 290. In this case, the auxiliary battery 215 and the DC / DC converter circuit 260 may also not be included. In the present embodiment, the secondary resonance circuit 240 is provided at a position facing the track 105, for example, on the lower surface of the electric vehicle 202. Note that when the power transmission circuit 120 is disposed on the side surface of the fixed facility, the secondary resonance circuit 240 may be provided on the side surface of the electric vehicle 202. The specific configuration of the power receiving device 200 including the secondary resonance circuit 240 will be described later.

[0015] The secondary resonance circuit 240 is connected to the power receiving circuit 230, and the AC power received by the secondary resonance circuit 240 is converted into DC power by the power receiving circuit 230. The battery 210, the high voltage side of the DC / DC converter circuit 260, and the inverter circuit 270 are connected to the output of the power receiving circuit 230. The auxiliary battery 215 and the auxiliary machine 290 are connected to the low voltage side of the DC / DC converter circuit 260. The motor generator 280 is connected to the inverter circuit 270. The DC power output from the power receiving circuit 230 can be used for charging the battery 210 and driving the motor generator 280 via the inverter circuit 270. Also, the DC power output from the power receiving circuit 230 can be stepped down using the DC / DC converter circuit 260 and used for charging the auxiliary battery 215 and driving the auxiliary machine 290.

[0016] The battery 210 is a secondary battery that outputs relatively high DC power, for example, a voltage from several tens of V to several hundreds of V, to drive the motor generator 280. The motor generator 280 operates as a three-phase AC motor and generates a driving force for the running of the electric vehicle 202. The motor generator 280 operates as a generator when the electric vehicle 202 decelerates and regenerates electric power. The inverter circuit 270 converts the power of the battery 210 into three-phase AC and supplies it to the motor generator 280 when the motor generator 280 operates as a motor. The inverter circuit 270 converts the three-phase AC regenerated by the motor generator 280 into DC and supplies it to the battery 210 when the motor generator 280 operates as a generator.

[0017] The DC / DC converter circuit 260 converts the output of the battery 210 into a voltage lower than the output voltage of the battery 210, for example, 12V, and supplies it to the auxiliary battery 215 and the auxiliary machine 290. The auxiliary battery 215 is a secondary battery for driving the auxiliary machine 290, and its voltage is relatively low. The auxiliary machine 290 includes peripheral devices of the electric vehicle 202 and various accessories of the electric vehicle 202.

[0018] The power reception side control unit 220 controls each part in addition to the inverter circuit 270 in the electric vehicle 202.

[0019] A-2. Circuit Configuration: As shown in FIG. 3, in addition to the above-described primary side resonance circuit 10, the power transmission circuit 120 includes a tertiary side resonance circuit 12, a power transmission side detection circuit 30, and a power transmission side control circuit 40. In FIG. 3, only one of the plurality of power transmission circuits 120 connected in parallel to the power supply device 110 is shown, and the illustration of the other power transmission circuits 120 is omitted.

[0020] The primary resonance circuit 10 includes a primary coil Ls1 and a first impedance variable element 20. The first impedance variable element 20 is connected in series with the primary coil Ls1 between the power supply device 110 and the primary coil Ls1, and constitutes the primary resonance circuit 10 together with the primary coil Ls1. The first impedance variable element 20 includes two capacitors C11, C12 and a first switch SW1. The capacitor C11 and the primary coil Ls1 are connected in series. The capacitor C12 and the first switch SW1 are connected in series, and the series-connected capacitor C12 and first switch SW1 are connected in parallel with the capacitor C11. The first switch SW1 may be configured to switch mechanical contacts such as a relay according to an external instruction, or may be configured to use a semiconductor element such as a MOS-FET or an analog switch.

[0021] The capacitance of the first impedance variable element 20 changes by switching the on / off state of the first switch SW1. When the first switch SW1 is on, the capacitor C12 is connected to the primary coil Ls1. At this time, the capacitance of the first impedance variable element 20 becomes equal to the sum of the capacitance of the capacitor C11 and the capacitance of the capacitor C12. Also, when the first switch SW1 is off, the capacitor C12 is disconnected from the primary coil Ls1. At this time, the capacitance of the first impedance variable element 20 becomes equal to the capacitance of the capacitor C11. By changing the capacitance of the first impedance variable element 20 in this way, the impedance of the primary resonance circuit 10 when the first switch SW1 is on decreases compared to when the first switch SW1 is off. Along with such a change in the impedance of the primary resonance circuit 10, the resonance state of the primary resonance circuit 10 also changes. In the present embodiment, the primary resonance circuit 10 is in a resonance state and a power transmission state at the operating frequency when the first switch SW1 is on. Also, the primary resonance circuit 10 is in a non-resonance state and a standby state at the operating frequency when the first switch SW1 is off. In the standby state, the power transmission circuit 120 causes a standby current smaller than the current flowing in the power transmission state to flow through the primary coil Ls1 to generate a magnetic flux. In the present embodiment, the first switch SW1 is configured as a normally open type switch, and the primary resonance circuit 10 maintains the standby state during normal times, more specifically, when the magnitude of the magnetic flux is less than the threshold value.

[0022] The primary resonance circuit 10 described above corresponds to the "first resonance circuit" in the present disclosure. Also, the primary coil Ls1 corresponds to the "first coil" in the present disclosure. Also, the capacitor C11 corresponds to the "first capacitor" in the present disclosure. Also, the capacitor C12 corresponds to the "second capacitor" in the present disclosure. Also, the first switch SW1 corresponds to the "switch element" in the present disclosure.

[0023] The tertiary resonance circuit 12 includes a tertiary coil Ls2 and a second impedance variable element 22 connected in parallel with the tertiary coil Ls2. The tertiary coil Ls2 is arranged such that in a resonant state, it is magnetically coupled to a primary coil Ls1 included in the primary resonance circuit 10 and a secondary coil Lr (to be described later) included in the secondary resonance circuit 240, respectively. The specific positional relationship between the primary coil Ls1 and the tertiary coil Ls2 will be described later.

[0024] Also, depending on the positional relationship between the primary coil Ls1 and the tertiary coil Ls2, either one of both ends of the tertiary coil Ls2 is connected to the power supply device 110. The specific manner of connecting the end of the tertiary coil Ls2 to the power supply device 110 will be described later.

[0025] The second impedance variable element 22 includes two capacitors C21 and C22 and a second switch SW2. The capacitor C22 and the second switch SW2 are connected in series with each other, and the capacitor C22 and the second switch SW2 connected in series with each other, the capacitor C21, and the tertiary coil Ls2 are connected in parallel with each other. The second switch SW2 may be configured to switch mechanical contacts such as a relay according to an external instruction, or may be configured to use a semiconductor element such as a MOS-FET or an analog switch.

[0026] The capacitance of the second impedance variable element 22 changes by switching the on / off state of the second switch SW2. The principle of capacitance change in the second impedance variable element 22 due to the switching of the second switch SW2 is the same as that of the first impedance variable element 20, so a detailed description is omitted. In the present embodiment, the second switch SW2 is configured as a normally open type switch, and the tertiary resonance circuit 12 maintains a standby state during normal times, more specifically, when the magnitude of the magnetic flux is less than the threshold value.

[0027] The above-described tertiary resonance circuit 12 corresponds to the "second resonance circuit" in the present disclosure. Also, the tertiary coil Ls2 corresponds to the "second coil" in the present disclosure. Also, the capacitor C21 corresponds to the "first capacitor" in the present disclosure. Also, the capacitor C22 corresponds to the "second capacitor" in the present disclosure. Also, the second switch SW2 corresponds to the "switch element" in the present disclosure.

[0028] The power transmission side detection circuit 30 includes a magnetic flux sensor that detects the magnitude of the magnetic flux linking the primary coil Ls1 and a current sensor that detects the magnitude of the current flowing through the primary coil. For convenience of illustration, in FIG. 3, the power transmission side detection circuit 30 is located away from the primary coil Ls1, but actually it is located in the vicinity of the primary coil Ls1. In the present embodiment, the magnetic flux sensor detects the magnitude of the magnetic flux by using the change in the voltage applied to the detection coil magnetically coupled to the primary coil Ls1. Also, the current sensor detects the magnitude of the current by using the change in the voltage applied to the capacitor C11. The power transmission side detection circuit 30 outputs a signal indicating the magnitude of the detected magnetic flux and a signal indicating the magnitude of the current to the power transmission side control circuit 40.

[0029] The power transmission side control circuit 40 drives the first switch SW1 and the second switch SW2 in response to the signals output from the power transmission side detection circuit 30 to switch the on / off states of the first switch SW1 and the second switch SW2. More specifically, when the magnitude of the magnetic flux indicated by the signal output from the power transmission side detection circuit 30 is equal to or greater than a preset threshold value, the power transmission side control circuit 40 turns on the first switch SW1 and the second switch SW2. Also, when the magnitude of the current indicated by the signal output from the power transmission side detection circuit 30 becomes equal to or less than the threshold value, the power transmission side control circuit 40 turns off the first switch SW1 and the second switch SW2.

[0030] The magnitude of the current and the magnitude of the magnetic flux change according to the degree of magnetic coupling between the power transmission circuit 120 and the power receiving device 200. In a non-resonant state, the magnitude of the magnetic flux increases as the power transmission circuit 120 and the power receiving device 200 approach each other. Also, in a resonant state, the magnitude of the current decreases as the power transmission circuit 120 and the power receiving device 200 approach each other. The threshold values of the magnitude of the magnetic flux and the magnitude of the current are specified and set in advance by performing simulation or the like as the values when the power receiving device 200 enters the power transmission area. The "power transmission area" means an area predetermined for each power transmission circuit 120 as an area where power transmission to the power receiving device 200 is executed. That is, the primary side control circuit 24 controls the switching of the first switch SW1 and the second switch SW2 so as to start power transmission when the power receiving device 200 enters the power transmission area. For this reason, power supply to the power transmission circuit 120 where the power receiving device 200 is not located in the power transmission area can be suppressed, and power consumption in the non-contact power supply system 1000 can be suppressed.

[0031] The circuit configuration of the power receiving device 200 will be described. In FIG. 3, among the circuit configurations of the power receiving device 200, the circuit configuration related to power supply to the battery 210 is particularly shown, and other parts are omitted. As shown in FIG. 3, the secondary side resonance circuit 240 is formed by connecting a secondary side coil Lr and a secondary side capacitor Cr in series. The secondary side resonance circuit 240 is configured to be in a resonant state at the operating frequency of the power transmission device 100. In a resonant state, the secondary side resonance circuit 240 receives AC power transmitted from the power transmission device 100 and supplies the received AC power to the power receiving circuit 230.

[0032] The power receiving circuit 230 includes a filter circuit 232 and a rectifier circuit 234. The filter circuit 232 suppresses the passage of noise components of the AC power input from the secondary-side resonance circuit 240 and allows the AC power in the target frequency band to pass through, and supplies a current of a constant magnitude to the rectifier circuit 234. The rectifier circuit 234 is configured as a diode bridge. The rectifier circuit 234 rectifies the AC power supplied from the secondary-side resonance circuit 240 and supplies the rectified DC power to the battery 210. The battery 210 is charged by being supplied with DC power from the rectifier circuit 234.

[0033] A-3. Coil Configuration: With reference to FIG. 4, the positional relationship between the primary-side coil Ls1 and the tertiary-side coil Ls2 in the present embodiment, and the mode of connection of the end portion of the tertiary-side coil Ls2 to the power supply device 110 according to such a positional relationship will be described. In FIG. 4, among the power supply device 110, the utility power supply PS is illustrated, and the illustration of other configurations is omitted. Also, the illustration of the power transmission-side detection circuit 30 and the power transmission-side control circuit 40 is omitted.

[0034] As shown in FIG. 4, the primary-side coil Ls1 is formed such that the planar coil Lp11 and the planar coil Lp12 overlap each other in the stacking direction. The planar coil Lp11 and the planar coil Lp12 are arranged with a predetermined interval d1 along the stacking direction. In the present embodiment, the planar coil Lp11 is located above the planar coil Lp12 in the stacking direction.

[0035] Similarly, the tertiary-side coil Ls2 is formed such that the planar coil Lp21 and the planar coil Lp22 overlap each other in the stacking direction. The planar coil Lp21 and the planar coil Lp22 are arranged with a predetermined interval d2 along the stacking direction. In the present embodiment, the planar coil Lp21 is located above the planar coil Lp22 in the stacking direction.

[0036] In this embodiment, the interval d1 and the interval d2 are of approximately the same magnitude. Note that the primary coil Ls1 and the tertiary coil Ls2 may be formed such that either one of the interval d1 and the interval d2 is larger than the other.

[0037] The primary coil Ls1 and the tertiary coil Ls2 are formed so as to overlap each other with a predetermined interval d3 therebetween along the stacking direction. Also, the tertiary coil Ls2 is located above the primary coil Ls1 in the stacking direction. Here, the "interval d3" means, in FIG. 4, the distance along the stacking direction between the planar coil Lp22 and the planar coil Lp11. That is, the interval d3 means the distance between the planar coil Lp22, which is the nearest coil having the smallest distance along the stacking direction from the primary coil Ls1 among the two planar coils Lp21 and Lp22 forming the tertiary coil Ls2, and the primary coil Ls1. More specifically, the interval d3 means the distance between the planar coil Lp11, which has the smallest distance along the stacking direction from the tertiary coil Ls2 among the primary coils Ls1, and the planar coil Lp22.

[0038] In this embodiment, the primary coil Ls1 and the tertiary coil Ls2 are arranged such that the distance d3 is greater than the distances d1 and d2. Thereby, compared with the form in which the distance d3 is of the same degree as the distances d1 and d2 and the form in which the distance d3 is smaller than the distances d1 and d2, the distance along the stacking direction between the primary coil Ls1 and the tertiary coil Ls2 can be increased, and as will be described later, an increase in the magnitude of the parasitic capacitance generated between the primary coil Ls1 and the tertiary coil Ls2 can be suppressed. When the magnitudes of the distances d1 and d2 are different, it is preferable that the primary coil Ls1 and the tertiary coil Ls2 be arranged such that the distance d3 is greater than the smaller one of the distances d1 and d2. In this embodiment, the primary coil Ls1 and the tertiary coil Ls2 are formed by a conductive pattern formed on a printed circuit board, and the above-described distances d1, d2, and d3 are defined by the thickness of the prepreg constituting the printed circuit board. The prepreg that separates the primary coil Ls1 and the tertiary coil Ls2 in this way corresponds to the "separation layer" in the present disclosure.

[0039] In the primary coil Ls1 and the tertiary coil Ls2 having the above-described positional relationship, when a current flows through the primary coil Ls1, a parasitic capacitance is generated between the planar coils Lp11 and Lp12 forming the primary coil Ls1 and the planar coils Lp21 and Lp22 forming the tertiary coil Ls2, and a leakage current is generated in the tertiary coil Ls2 through the parasitic capacitance. In the following description, the parasitic capacitance generated between the planar coil Lp11 and the planar coil Lp21 is referred to as "parasitic capacitance Cs11", the parasitic capacitance generated between the planar coil Lp11 and the planar coil Lp22 is referred to as "parasitic capacitance Cs12", the parasitic capacitance generated between the planar coil Lp12 and the planar coil Lp21 is referred to as "parasitic capacitance Cs21", and the parasitic capacitance generated between the planar coil Lp12 and the planar coil Lp22 is referred to as "parasitic capacitance Cs22". In the present embodiment, among the planar coils that generate the above parasitic capacitance, the distance between the planar coil Lp11 and the planar coil Lp22, which is the closest coil, is the smallest. Therefore, among the above parasitic capacitances, the parasitic capacitance Cs12 generated between the planar coil Lp11 and the planar coil Lp22 has the largest capacitance. That is, in the present embodiment, the magnitude of the leakage current through the parasitic capacitance Cs12 is larger than the magnitude of the leakage current through the other parasitic capacitances.

[0040] As shown in FIG. 4, in the present embodiment, an end portion of the planar coil Lp22, which is the closest coil, is connected to the system power supply PS between the first impedance variable element 20 and the system power supply PS. The effect achieved by such a connection mode will be described with reference to FIG. 5, which schematically shows the connection mode shown in FIG. 4. By connecting the end portion of the planar coil Lp22 to the system power supply PS, as shown in FIG. 5, the current path of the leakage current passing through the tertiary coil Ls2 is system power supply PS - planar coil Lp11 - parasitic capacitance Cs12 - planar coil Lp22 - system power supply PS. Thus, according to the connection mode of the present embodiment, since it is possible to prevent the largest leakage current through the parasitic capacitance Cs12 having the largest capacitance from passing through the planar coil Lp21, the current path of the leakage current flowing through the tertiary coil Ls2 can be shortened, and an increase in the leakage electromagnetic field caused by the leakage current can be suppressed.

[0041] According to the non-contact power supply system 1000 of the first embodiment described above, the end of the planar coil Lp22, which is the closest coil, is connected to the power supply device 110 between the power supply device 110 and the first impedance variable element 20. As a result, the current path of the leakage current passing through the secondary coil Ls2 is system power supply PS - planar coil Lp11 - floating capacitance Cs12 - planar coil Lp22 - system power supply PS. Therefore, since it is possible to prevent the maximum leakage current from passing through the planar coil Lp21 via the floating capacitance Cs12 having the maximum capacitance, the current path of the leakage current flowing through the secondary coil Ls2 can be shortened, and an increase in the leakage electromagnetic field caused by the leakage current can be suppressed.

[0042] Also, since the interval d3 is larger than the intervals d1 and d2, the distance along the stacking direction between the primary coil Ls1 and the secondary coil Ls2 can be increased compared to a form in which the interval d3 is of the same degree as the intervals d1 and d2, and a form in which the interval d3 is smaller than the intervals d1 and d2, and an increase in the magnitude of the floating capacitance generated between the primary coil Ls1 and the secondary coil Ls2 can be suppressed.

[0043] Further, the power transmission circuit 120 includes the first impedance variable element 20 and the second impedance variable element 22, and the first impedance variable element 20 and the second impedance variable element 22 switch the states of the primary resonance circuit 10 or the secondary resonance circuit 12 between a resonance state and a non-resonance state according to the positional relationship with the power receiving device 200. Therefore, when the positional relationship with the power receiving device 200 is a positional relationship in which power transmission is not executed, the states of the primary resonance circuit 10 and the secondary resonance circuit 12 are switched to the non-resonance state, and power supply to the power transmission circuit 120 is suppressed, so an increase in power consumption in the non-contact power supply system 1000 can be suppressed.

[0044] Also, since the primary coil Ls1 and the secondary coil Ls2 are separated by a separation layer, the space between the primary coil Ls1 and the secondary coil Ls2 can be separated compared to a form without a separation layer, and an increase in the magnitude of the floating capacitance Cs11 generated between the primary coil Ls1 and the secondary coil Ls2 can be suppressed.

[0045] B. Second Embodiment: The power transmission circuit 120A included in the power transmission device 100A of the second embodiment is different from the power transmission circuit 120 of the first embodiment in that the end of the closest coil is connected to the system power supply PS between the system power supply PS and the primary coil Ls1. Since the circuit configuration of the power transmission circuit 120A of the second embodiment is the same as that of the power transmission circuit 120 of the first embodiment, the same components are denoted by the same reference numerals, and detailed description thereof is omitted.

[0046] In the power transmission circuit 120A shown in FIG. 6, the end of the planar coil Lp22, which is the closest coil, is connected to the system power supply PS between the system power supply PS and the primary coil Ls1. The effects achieved by such a connection mode will be described with reference to FIG. 7, which schematically shows the connection mode shown in FIG. 6. As shown in FIG. 7, by connecting the end of the planar coil Lp22 to the system power supply PS, the potentials of the planar coil Lp11 and the planar coil Lp22 that generate the floating capacitance Cs12 having the maximum capacitance can be made the same. Therefore, in the secondary coil Ls2, it is possible to suppress the flow of the maximum leakage current through the floating capacitance Cs12, and to suppress an increase in the leakage electromagnetic field caused by the leakage current.

[0047] According to the non-contact power supply system 1000 including the power transmission device 100A of the second embodiment described above, the end of Lp22, which is the closest coil, is connected to the system power supply PS between the system power supply PS and the primary coil Ls1. For this reason, the potentials of the planar coil Lp11 and the planar coil Lp22 that generate the floating capacitance Cs12 having the maximum capacitance can be made the same. Therefore, in the secondary coil Ls2, it is possible to suppress the flow of the maximum leakage current through the floating capacitance Cs12, and to suppress an increase in the leakage electromagnetic field caused by the leakage current.

[0048] C. Other Embodiments: In each of the above embodiments, the primary coil Ls1 and the tertiary coil Ls2 are formed so as to overlap each other along the stacking direction as shown in FIGS. 4 and 6, but the present disclosure is not limited thereto. As shown in FIGS. 8 and 9, the primary coil Ls1 and the tertiary coil Ls2 may be arranged in an empty region inside the radial direction of the primary coil Ls1 in the same layer.

[0049] Since FIGS. 8 and 9 have the same configuration as each other except for the connection mode of the end portion of the tertiary coil Ls2 to the system power supply PS, the configuration of the primary coil Ls1 and the tertiary coil Ls2 will be described more specifically with reference to FIG. 8. In FIG. 8, the primary coil Ls1 is formed by winding a planar coil Lp11 and a planar coil Lp12 in the same layer. The planar coil Lp11 and the planar coil Lp12 are formed such that the conductors forming the respective planar coils overlap each other with a predetermined interval d4 along the radial direction. Further, in the present embodiment, the planar coil Lp11 is located inside the radial direction of the planar coil Lp12.

[0050] Similarly, the tertiary coil Ls2 is formed by winding a planar coil Lp21 and a planar coil Lp22 in the same layer. The planar coil Lp21 and the planar coil Lp22 are formed such that the conductors forming the respective planar coils overlap each other with a predetermined interval d5 along the radial direction. Further, in the present embodiment, the planar coil Lp21 is located inside the radial direction of the planar coil Lp22. In the present embodiment, the interval d4 and the interval d5 are of the same magnitude. Note that the primary coil Ls1 and the tertiary coil Ls2 may be formed such that either one of the interval d4 and the interval d5 is larger than the other.

[0051] The primary coil Ls1 and the secondary coil Ls2 are formed so as to overlap each other with a predetermined interval d6 along the radial direction. Here, the "interval d6" means, in FIG. 8, the distance along the radial direction between the conductor forming the planar coil Lp22 and the conductor forming the planar coil Lp11. That is, the interval d6 means the distance along the radial direction between the conductor forming the planar coil Lp22, which is the closest coil having the smallest distance along the radial direction from the primary coil Ls1 among the two planar coils Lp21 and Lp22 forming the secondary coil Ls2, and the conductor forming the primary coil Ls1. More specifically, the interval d6 means the distance along the radial direction between the conductor forming the planar coil Lp11, which has the smallest distance from the conductor forming the secondary coil Ls2 among the conductors forming the primary coil Ls1, and the conductor forming the planar coil Lp22. In such a positional relationship, the stray capacitance Cs12 formed between the planar coil Lp22, which is the closest coil, and the planar coil Lp11 has the maximum capacitance.

[0052] In the present embodiment, the primary coil Ls1 and the secondary coil Ls2 are arranged such that the interval d6 is larger than the intervals d4 and d5. Thereby, compared with the form in which the interval d6 is of the same degree as the intervals d4 and d5 and the form in which the interval d6 is smaller than the intervals d4 and d5, the distance along the radial direction between the primary coil Ls1 and the secondary coil Ls2 can be increased, and an increase in the magnitude of the stray capacitance generated between the primary coil Ls1 and the secondary coil Ls2 can be suppressed.

[0053] In the power transmission circuit 120B shown in FIG. 8, the end portion of the planar coil Lp22, which is the closest coil, is connected to the system power supply PS between the first impedance variable element 20 and the system power supply PS. When such a connection mode is schematically shown, the circuit configuration is the same as that of FIG. 5 described above. Thus, the non-contact power supply system 1000 including the power transmission device 100B having the power transmission circuit 120B shown in FIG. 8 also exhibits the same effects as those of the first embodiment.

[0054] On the other hand, in the power transmission circuit 120C shown in FIG. 9, the end of the planar coil Lp22, which is the closest coil, is connected to the system power supply PS between the system power supply PS and the primary coil Ls1. When such a connection mode is schematically shown, the circuit configuration is the same as that in FIG. 7 described above. Thus, the non-contact power supply system 1000 including the power transmission device 100C having the power transmission circuit 120C shown in FIG. 9 also exhibits the same effects as those in the second embodiment.

[0055] (C2) In the forms shown in FIGS. 4 and 6 described above, the planar coil Lp11 is arranged above the planar coil Lp12 in the stacking direction of the primary coil Ls1, and the planar coil Lp21 is arranged above the planar coil Lp22 in the stacking direction of the secondary coil Ls2. Also, in the forms shown in FIGS. 8 and 9 described above, the planar coil Lp11 is arranged inside the planar coil Lp12 in the radial direction of the primary coil Ls1, and the planar coil Lp21 is arranged inside the planar coil Lp22 in the radial direction of the secondary coil Ls2. However, the positional relationship between the planar coil Lp11 and the planar coil Lp12 in the primary coil Ls1 and the positional relationship between the planar coil Lp21 and the planar coil Lp22 in the secondary coil Ls2 are not limited to the above-described positional relationships.

[0056] In FIGS. 10 and 11, the planar coil Lp22 is arranged above the planar coil Lp21 in the stacking direction. In such a positional relationship, the planar coil Lp21 corresponds to the closest coil, and the parasitic capacitance Cs11 has the maximum capacitance.

[0057] In the power transmission circuit 120D shown in FIG. 10, the end of the planar coil Lp21, which is the closest coil, is connected to the system power supply PS between the first impedance variable element 20 and the system power supply PS. The effect achieved by such a connection mode will be described with reference to FIG. 12, which schematically shows the connection mode shown in FIG. 10. By connecting the end of the planar coil Lp21 to the system power supply PS, as shown in FIG. 12, the current path of the leakage current passing through the tertiary coil Ls2 is: system power supply PS - planar coil Lp11 - parasitic capacitance Cs11 - planar coil Lp21 - system power supply PS. Thus, according to the connection mode of the present embodiment, since the leakage current is prevented from passing through the planar coil Lp22, the current path of the leakage current flowing through the tertiary coil Ls2 can be shortened, and an increase in the leakage magnetic field caused by the leakage current through the parasitic capacitance Cs11 can be suppressed. That is, the non-contact power supply system 1000 including the power transmission device 100D having the power transmission circuit 120D shown in FIG. 10 also exhibits the same effect as the first embodiment.

[0058] In the power transmission circuit 120E shown in FIG. 11, the end of the planar coil Lp21, which is the closest coil, is connected to the system power supply PS between the system power supply PS and the primary coil Ls1. The effect achieved by such a connection mode will be described with reference to FIG. 13, which schematically shows the connection mode shown in FIG. 11. By connecting the end of the planar coil Lp21 to the system power supply PS as shown in FIG. 13, the potentials of the planar coil Lp11 that generates the parasitic capacitance Cs11 having the maximum capacitance and the planar coil Lp21 can be made the same, so that the leakage current through the parasitic capacitance Cs11 can be suppressed, and an increase in the leakage magnetic field caused by the leakage current can be suppressed. Thus, the non-contact power supply system 1000 including the power transmission device 100E having the power transmission circuit 120E shown in FIG. 11 also exhibits the same effect as the second embodiment.

[0059] In FIGS. 14 and 15, a planar coil Lp22 is arranged inside the planar coil Lp21 in the radial direction. In such a positional relationship, the planar coil Lp21 corresponds to the closest coil, and the parasitic capacitance Cs11 has the maximum capacitance.

[0060] In the power transmission circuit 120F shown in FIG. 14, the end of the planar coil Lp21, which is the closest coil, is connected to the system power supply PS between the first impedance variable element 20 and the system power supply PS. When such a connection mode is schematically shown, the circuit configuration is the same as that of FIG. 12 described above. Thus, the non-contact power supply system 1000 including the power transmission device 100F having the power transmission circuit 120F shown in FIG. 14 also exhibits the same effects as those of the first embodiment.

[0061] In the power transmission circuit 120G shown in FIG. 15, the end of the planar coil Lp21, which is the closest coil, is connected to the system power supply PS between the system power supply PS and the primary coil Ls1. When such a connection mode is schematically shown, the circuit configuration is the same as that of FIG. 13 described above. Thus, the non-contact power supply system 1000 including the power transmission device 100G having the power transmission circuit 120G shown in FIG. 15 also exhibits the same effects as those of the second embodiment.

[0062] In FIGS. 16 and 17, the planar coil Lp12 is arranged above the planar coil Lp11 in the stacking direction, and the planar coil Lp22 is arranged above the planar coil Lp21 in the stacking direction. In such a positional relationship, the planar coil Lp21 corresponds to the closest coil, and the stray capacitance Cs21 has the maximum capacitance.

[0063] In the power transmission circuit 120H shown in FIG. 16, the end of the planar coil Lp21, which is the closest coil, is connected to the system power supply PS between the first impedance variable element 20 and the system power supply PS. The effect achieved by such a connection mode will be described with reference to FIG. 18, which schematically shows the connection mode shown in FIG. 16. By connecting the end of the planar coil Lp21 to the system power supply PS, as shown in FIG. 18, the current path of the leakage current passing through the tertiary coil Ls2 is: system power supply PS - planar coil Lp12 - parasitic capacitance Cs21 - planar coil Lp21 - system power supply PS. Thus, according to the connection mode of the present embodiment, since the leakage current is prevented from passing through the planar coil Lp22, the current path of the leakage current flowing through the tertiary coil Ls2 can be shortened, and an increase in the leakage electromagnetic field caused by the leakage current through the parasitic capacitance Cs21 can be suppressed. That is, the non-contact power supply system 1000 including the power transmission device 100H having the power transmission circuit 120H shown in FIG. 16 also exhibits the same effect as the first embodiment.

[0064] In the power transmission circuit 120I shown in FIG. 17, the end of the planar coil Lp21, which is the closest coil, is connected to the system power supply PS between the system power supply PS and the primary coil Ls1. When such a connection mode is schematically shown, the circuit configuration is the same as that of FIG. 13 described above. Thus, the non-contact power supply system 1000 including the power transmission device 100I having the power transmission circuit 120I shown in FIG. 17 also exhibits the same effect as the second embodiment.

[0065] In FIGS. 19 and 20, the planar coil Lp12 is arranged inside the planar coil Lp11 in the radial direction, and the planar coil Lp22 is arranged inside the planar coil Lp21 in the radial direction. In such a positional relationship, the planar coil Lp21 corresponds to the closest coil, and the parasitic capacitance Cs21 has the maximum capacitance.

[0066] In the power transmission circuit 120J shown in FIG. 19, the end of the planar coil Lp21, which is the closest coil, is connected to the system power supply PS between the first impedance variable element 20 and the system power supply PS. When such a connection mode is schematically shown, the circuit configuration is the same as that of FIG. 18 described above. Thus, the non-contact power supply system 1000 including the power transmission device 100J having the power transmission circuit 120J shown in FIG. 19 also exhibits the same effects as those of the first embodiment.

[0067] In the power transmission circuit 120K shown in FIG. 20, the end of the planar coil Lp21, which is the closest coil, is connected to the system power supply PS between the system power supply PS and the primary coil Ls1. When such a connection mode is schematically shown, the circuit configuration is the same as that of FIG. 13 described above. Thus, the non-contact power supply system 1000 including the power transmission device 100K having the power transmission circuit 120K shown in FIG. 20 also exhibits the same effects as those of the second embodiment.

[0068] In FIGS. 21 and 22, the planar coil Lp12 is arranged above the planar coil Lp11 in the stacking direction. In such a positional relationship, the planar coil Lp22 corresponds to the closest coil, and the parasitic capacitance Cs22 has the maximum capacitance.

[0069] In the power transmission circuit 120L shown in FIG. 21, the end of the planar coil Lp22, which is the closest coil, is connected to the system power supply PS between the first impedance variable element 20 and the system power supply PS. The effect achieved by such a connection mode will be described with reference to FIG. 23, which schematically shows the connection mode shown in FIG. 21. By connecting the end of the planar coil Lp22 to the system power supply PS, as shown in FIG. 23, the current path of the leakage current passing through the tertiary coil Ls2 is: system power supply PS - planar coil Lp12 - stray capacitance Cs22 - planar coil Lp22 - system power supply PS. Thus, according to the connection mode of the present embodiment, since the leakage current through the stray capacitance Cs22 is prevented from passing through the planar coil Lp21, the current path of the leakage current flowing through the tertiary coil Ls2 can be shortened, and an increase in the leakage electromagnetic field caused by the leakage current can be suppressed. Thus, the non-contact power supply system 1000 including the power transmission device 100L having the power transmission circuit 120L shown in FIG. 21 also exhibits the same effect as the first embodiment.

[0070] In the power transmission circuit 120M shown in FIG. 22, the end of the planar coil Lp22, which is the closest coil, is connected to the system power supply PS between the system power supply PS and the primary coil Ls1. When such a connection mode is schematically shown, it has the same circuit configuration as FIG. 7 described above. Thus, the non-contact power supply system 1000 including the power transmission device 100M having the power transmission circuit 120M shown in FIG. 22 also exhibits the same effect as the second embodiment.

[0071] In FIGS. 24 and 25, the planar coil Lp12 is arranged radially inside the planar coil Lp11. In such a positional relationship, the planar coil Lp22 corresponds to the closest coil, and the stray capacitance Cs22 has the maximum capacitance.

[0072] In the power transmission circuit 120N shown in FIG. 24, the end of the planar coil Lp22, which is the closest coil, is connected to the system power supply PS between the first impedance variable element 20 and the system power supply PS. When such a connection mode is schematically shown, the circuit configuration is the same as that of FIG. 23 described above. Thus, the non-contact power supply system 1000 including the power transmission device 100N having the power transmission circuit 120N shown in FIG. 24 also exhibits the same effects as those of the first embodiment.

[0073] In the power transmission circuit 120O shown in FIG. 25, the end of the planar coil Lp22, which is the closest coil, is connected to the system power supply PS between the system power supply PS and the primary coil Ls1. When such a connection mode is schematically shown, the circuit configuration is the same as that of FIG. 7 described above. Thus, the non-contact power supply system 1000 including the power transmission device 100O having the power transmission circuit 120O shown in FIG. 25 also exhibits the same effects as those of the second embodiment.

[0074] (C3) In the form in which the primary coil Ls1 and the tertiary coil Ls2 are arranged to overlap in the stacking direction as described above, the tertiary coil Ls2 is arranged above the primary coil Ls1 in the stacking direction, but the present disclosure is not limited thereto. The tertiary coil Ls2 may be arranged below the primary coil Ls1 in the stacking direction. Even in such a form, by connecting the end of the closest coil to the system power supply PS between the first impedance variable element 20 and the system power supply PS, the same effects as those of the first embodiment are achieved. Also, by connecting the end of the closest coil to the system power supply PS between the primary coil Ls1 and the system power supply PS, the same effects as those of the second embodiment are achieved.

[0075] (C4) In the form where the primary coil Ls1 and the tertiary coil Ls2 are arranged in the same layer as described above, the tertiary coil Ls2 is arranged in the space radially inside the primary coil Ls1, but the present disclosure is not limited to this. The primary coil Ls1 may be arranged in the space radially inside the tertiary coil Ls2. Even in such a form, by connecting the end of the closest coil to the system power supply PS between the first impedance variable element 20 and the system power supply PS, the same effect as in the first embodiment can be achieved. Also, by connecting the end of the closest coil to the system power supply PS between the primary coil Ls1 and the system power supply PS, the same effect as in the second embodiment can be achieved.

[0076] (C5) In the above embodiment, the primary coil Ls1 and the tertiary coil Ls2 are formed by a conductive pattern formed on a printed circuit board, but the present disclosure is not limited to this. The primary coil Ls1 and the tertiary coil Ls2 may be formed by a litz wire. In such a form, the air layer existing between each winding layer of the wound litz wire corresponds to the "separation layer" in the present disclosure. Note that each winding layer may be separated by resin or the like, and in such a form, the resin layer existing between each winding layer corresponds to the separation layer.

[0077] The present disclosure is not limited to the above-described embodiments, and can be realized in various configurations without departing from the gist thereof. For example, the technical features in each embodiment corresponding to the technical features in the form described in the summary of the invention can be appropriately replaced or combined in order to solve some or all of the above-described problems, or to achieve some or all of the above-described effects. Also, if the technical feature is not described as essential in this specification, it can be appropriately deleted. (Form 1) A power transmission circuit (120 to 120O) for non-contact power supply to a power reception device (200), A first resonance circuit (10), A first coil (Ls1) connected to a power supply device (110) that supplies AC power at a predetermined operating frequency, A first impedance variable element (20) connected in series with the first coil between the first coil and the power supply device for switching the state of the first resonance circuit between a resonance state and a non-resonance state; A first resonance circuit having; A second resonance circuit (12), A second coil (Ls2) magnetically coupled to the first coil, A second impedance variable element (22) connected in parallel with the second coil for switching the state of the second resonance circuit between a resonance state and a non-resonance state; A second resonance circuit having; Comprising, One of both ends of the second coil is connected to the power supply device, Power transmission circuit. (Embodiment 2) The power transmission circuit according to Embodiment 1, The first coil and the second coil are each formed such that a plurality of planar coils (Lp11, Lp12, Lp21, Lp22) overlap in the stacking direction, Of the first coil and the second coil, one coil is arranged apart from the other coil in the stacking direction, Of the plurality of planar coils forming the second coil, an end portion of the closest coil, which is the planar coil having the smallest distance along the stacking direction between the planar coil and the first coil, is connected to the power supply device between the power supply device and the first impedance variable element. Power transmission circuit. (Embodiment 3) The power transmission circuit according to Embodiment 1, The first coil and the second coil are each formed such that a plurality of planar coils overlap in the stacking direction, Of the first coil and the second coil, one coil is arranged apart from the other coil in the stacking direction, Of the plurality of planar coils forming the second coil, the end of the closest coil, which is the planar coil with the smallest distance along the stacking direction between the planar coil and the first coil, is connected to the power supply device between the power supply device and the first coil. Power transmission circuit. (Embodiment 4) A power transmission circuit according to Embodiment 2 or Embodiment 3, The distance (d3) along the stacking direction between the closest coil and the first coil is greater than the smaller of the distance (d1) along the stacking direction between the plurality of planar coils forming the first coil and the distance (d2) along the stacking direction between the plurality of planar coils forming the second coil. Power transmission circuit. (Embodiment 5) A power transmission circuit according to Embodiment 1, The first coil and the second coil are each formed by a plurality of planar coils wound in the same layer, Of the first coil and the second coil, one coil is arranged in the free space radially inside the other coil in the same layer, Of the plurality of planar coils forming the second coil, the end of the closest coil, which is the planar coil with the smallest distance along the radial direction between the conductor forming the planar coil and the conductor forming the first coil, is connected to the power supply device between the power supply device and the first impedance variable element. Power transmission circuit. (Embodiment 6) A power transmission circuit according to Embodiment 1, The first coil and the second coil are each formed by a plurality of planar coils wound in the same layer, Of the first coil and the second coil, one coil is arranged in the free space radially inside the other coil in the same layer, Of the plurality of planar coils forming the second coil, the end of the closest coil, which is the planar coil having the smallest distance along the radial direction between the conductor forming the planar coil and the conductor forming the first coil, is connected to the power supply device between the power supply device and the first coil. Power transmission circuit. (Embodiment 7) A power transmission circuit according to Embodiment 5 or Embodiment 6, wherein the distance (d6) along the radial direction between the conductor forming the closest coil and the conductor forming the first coil is greater than the smaller of the distance (d4) along the radial direction between the conductors forming the first coil and the distance (d5) along the radial direction between the conductors forming the second coil. Power transmission circuit. (Embodiment 8) A power transmission circuit according to any one of Embodiments 1 to 7, wherein each of the first impedance variable element and the second impedance variable element includes a first capacitor (C11, C21), and a second capacitor (C12, C22) and a switch element (SW1, SW2) connected in parallel to the first capacitor, and the second capacitor and the switch element connected in series with each other. the first impedance variable element switches the state of the first resonance circuit between a resonance state and a non-resonance state according to the positional relationship with the power receiving device. the second impedance variable element switches the state of the second resonance circuit between a resonance state and a non-resonance state according to the positional relationship with the power receiving device. Power transmission circuit. (Embodiment 9) A power transmission circuit according to any one of Embodiments 1 to 7, wherein the first coil and the second coil are separated by a separation layer. Power transmission circuit. (Embodiment 10) A power transmission circuit according to any one of Embodiments 1 to 7, wherein the first coil and the second coil are formed of Litz wire. Power transmission circuit. (Embodiment 11) A power transmission circuit according to any one of Embodiments 1 to 7, wherein the first coil and the second coil are formed by a conductive pattern formed on a printed circuit board. Power transmission circuit. (Embodiment 12) A power transmission device (100 - 100O) that supplies power to a power receiving device in a non-contact manner, a power transmission circuit according to Embodiment 1, and a power supply device that supplies AC power having a predetermined operating frequency to the power transmission circuit. The power transmission device includes: Power transmission device. (Embodiment 13) A power receiving device, which is powered in a non-contact manner from the power transmission device according to Embodiment 12. Power receiving device. (Embodiment 14) A non-contact power supply system (1000), including a power transmission device according to Embodiment 12, and a power receiving device according to Embodiment 13. The non-contact power supply system includes: Non-contact power supply system.

Explanation of Reference Numerals

[0078] 10... Primary resonance circuit, 12... Tertiary resonance circuit, 20... First impedance variable element, 22... Second impedance variable element, 110... Power supply device, 120 - 120O... Power transmission circuit, 200... Power receiving device

Claims

1. A power transmission circuit (120-120O) for contactlessly supplying power to a power receiving device (200), A first resonant circuit (10), a first coil (Ls1) connected to a power supply device (110) that supplies AC power at a predetermined operating frequency; a first variable impedance element (20) connected in series with the first coil between the first coil and the power supply device, for switching the state of the first resonant circuit between a resonant state and a non-resonant state; a first resonant circuit having A second resonant circuit (12), a second coil (Ls2) magnetically coupled to the first coil; a second impedance variable element (22) connected in parallel with the second coil for switching the state of the second resonant circuit between a resonant state and a non-resonant state; a second resonant circuit having Equipped with One of both ends of the second coil is connected to the power supply device. Power transmission circuit.

2. The power transmission circuit according to claim 1, The first coil and the second coil are each formed so that a plurality of planar coils (Lp11, Lp12, Lp21, Lp22) are stacked in a stacking direction, one of the first coil and the second coil is disposed apart from the other coil in the stacking direction, an end of a closest coil, which is the planar coil among the plurality of planar coils forming the second coil and which is the planar coil having the smallest distance between the planar coil and the first coil in the stacking direction, is connected to the power supply device between the power supply device and the first variable impedance element; Power transmission circuit.

3. The power transmission circuit according to claim 1, the first coil and the second coil are each formed so that a plurality of planar coils are stacked in a stacking direction, one of the first coil and the second coil is disposed apart from the other coil in the stacking direction, an end of a closest coil, which is the planar coil among the plurality of planar coils forming the second coil and which is the planar coil having the smallest distance between the planar coil and the first coil along the stacking direction, is connected to the power supply device between the power supply device and the first coil; Power transmission circuit.

4. The power transmission circuit according to claim 2 or 3, a distance (d3) between the nearest coil and the first coil along the stacking direction is greater than a smaller distance between a distance (d1) between the plurality of planar coils forming the first coil along the stacking direction and a distance (d2) between the plurality of planar coils forming the second coil along the stacking direction; Power transmission circuit.

5. The power transmission circuit according to claim 1, the first coil and the second coil are each formed by a plurality of planar coils wound in the same layer, one of the first coil and the second coil is disposed in an empty space radially inside the other coil in the same layer, an end of a closest coil, which is a planar coil having a smallest distance along the radial direction between a conductor forming the planar coil and a conductor forming the first coil, among the plurality of planar coils forming the second coil, is connected to the power supply device between the power supply device and the first variable impedance element; Power transmission circuit.

6. The power transmission circuit according to claim 1, the first coil and the second coil are each formed by a plurality of planar coils wound in the same layer, one of the first coil and the second coil is disposed in an empty space radially inside the other coil in the same layer, an end of a closest coil, which is a planar coil having a smallest distance along the radial direction between a conductor forming the planar coil and a conductor forming the first coil, among the plurality of planar coils forming the second coil, is connected to the power supply device between the power supply device and the first coil; Power transmission circuit.

7. The power transmission circuit according to claim 5 or 6, a distance (d6) along the radial direction between the conductors forming the nearest coil and the conductors forming the first coil is greater than a smaller distance between a distance (d4) along the radial direction between the conductors forming the first coil and a distance (d5) along the radial direction between the conductors forming the second coil; Power transmission circuit.

8. The power transmitting circuit according to any one of claims 1 to 3, 5, and 6, the first variable impedance element and the second variable impedance element each have a first capacitor (C11, C21), a second capacitor (C12, C22) connected in parallel to the first capacitor, and a switch element (SW1, SW2) connected in series to each other; the first variable impedance element switches a state of a first resonant circuit between a resonant state and a non-resonant state depending on a positional relationship with the power receiving device; the second variable impedance element switches the state of the second resonant circuit between a resonant state and a non-resonant state depending on a positional relationship with the power receiving device; Power transmission circuit.

9. The power transmitting circuit according to any one of claims 1 to 3, 5, and 6, The first coil and the second coil are separated by a separation layer. Power transmission circuit.

10. The power transmitting circuit according to any one of claims 1 to 3, 5, and 6, The first coil and the second coil are formed of Litz wire. Power transmission circuit.

11. The power transmitting circuit according to any one of claims 1 to 3, 5, and 6, the first coil and the second coil are formed by conductive patterns formed on a printed circuit board; Power transmission circuit.

12. A power transmitting device (100-100O) that wirelessly supplies power to a power receiving device, The power transmitting circuit according to claim 1; a power supply device that supplies AC power at a predetermined operating frequency to the power transmission circuit; Equipped with Power transmission equipment.

13. A contactless power supply system (1000), A power transmission device comprising: the power transmission device according to claim 12; Contactless power supply system.

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