JP2017005790A - Wireless power transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wireless power transmission system in which variation in the voltage across a load for the variation in the equivalent resistance of the load is suppressed.SOLUTION: A wireless power transmission system includes a transmission side resonance circuit 130 having a power transmission coil L1 and a transmission side capacitor C1, a driver circuit 120 for supplying the transmission side resonance circuit with an AC current at a drive frequency, a reception side resonance circuit 230 having a power reception coil L2 and a reception side capacitor C2, and a load to which power is supplied from the power reception side resonance circuit. When viewing the power transmission side resonance circuit from the driver circuit, the formula of F matrix of a four-terminal network, constituted of the power transmission side resonance circuit and power reception side resonance circuit, is satisfied.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wireless power transmission system.

  For example, a wireless power feeding technique for supplying a large amount of power wirelessly from the outside to a battery of an electric vehicle, for example, without using a power cable has attracted attention.

  Non-Patent Document 1 proposes a method of transmitting power wirelessly using a method of electromagnetically resonating a power transmitting device and a power receiving device at the same resonance frequency.

Karalis A. et al (Wireless Power Transfer via Strongly Coupled Magnetic Resonances) Science, vol 317, no. 5834, pp. 83-86, 2007.

In Non-Patent Document 1, the power P _DS transmitted wirelessly from the power transmission side to the power reception side is indicated by P _DS ≡−iωMI _{S ID} . Here, when the voltage across the load Vo, the equivalent resistance of the load and RL, the power P _DS transmitted wirelessly to the receiving side from the transmitting side is consumed by all the load, the power P _DS is P _{DS =} Vo ² / RL. When this is substituted into the equation shown in Non-Patent Document 1 and expressed as an absolute value, the voltage across the load is Vo ² = ω · M · Is · _ID · RL. In other words, even if the mutual inductance M indicating the frequency ω of the power transmission device and the electromagnetic coupling state between the power transmission device and the power reception device is fixed, the voltage Vo across the load may vary depending on the state of the equivalent resistance RL of the load. is there.

  However, in the technique disclosed in Non-Patent Document 1, no consideration is given to fluctuations in the equivalent resistance RL of the load, and the voltage across the load varies greatly depending on the state of the equivalent resistance RL of the load. was there.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a wireless power transmission system in which fluctuations in the voltage across the load with respect to fluctuations in the equivalent resistance of the load are suppressed.

  A wireless power transmission system according to the present invention is a wireless power transmission system that wirelessly transmits AC power from a power transmission device to a power reception device, and the power transmission device includes a power transmission coil and a power transmission side capacitor unit. And a drive circuit that supplies an alternating current to the power transmission side resonance circuit at a drive frequency, and the power reception device includes a power reception side resonance circuit having a power reception coil and a power reception side capacitor, and power from the power reception side resonance circuit. And when the power transmission side resonance circuit is viewed from the drive circuit, an F matrix of a four-terminal network composed of the power transmission side resonance circuit and the power reception side resonance circuit is expressed by Equation (1), The real part of A in the F matrix of the network is Ra, the imaginary part is Xa, the real part of B in the F matrix of the four-terminal network is Rb, the imaginary part is Xb, and the equivalent resistance of the load is RL0. Helix A and B, the following equation (2), (3), and satisfies the (4).

（但し、ｊ^２＝−１である。）

(However, j ² = −1.)

  According to the present invention, A and B of an F matrix of a four-terminal network composed of a power transmission side resonance circuit and a power reception side resonance circuit of a wireless power transmission system are expressed by the following equations (2), (3), and (4). Since the four-terminal network is configured so as to satisfy, the change in the voltage across the load can be suppressed to ± 10% or less even if the load fluctuates. Specifically, when the load is a power supply circuit such as a battery charger, the input voltage allowable range of the power supply circuit is normally defined as ± 10%, and input of a voltage exceeding that range is applied to the components constituting the power supply circuit. On the other hand, there is a risk of applying a high load or stopping the operation. The wireless power transmission system according to the present invention suppresses fluctuations in the input voltage of the power supply circuit that is the load to ± 10% or less, which is the allowable input voltage range of the power supply circuit, even if the equivalent resistance of the power supply circuit that is the load varies. be able to. That is, the fluctuation of the voltage across the load can be suppressed with respect to the fluctuation of the equivalent resistance of the load.

  Preferably, the drive frequency is f, the change in the drive frequency f is δf, the imaginary part of the impedance of the wireless power transmission network composed of the power transmission side resonance circuit, the power reception side resonance circuit and the load is X, and the drive frequency of the imaginary part X If the change with respect to f is δX, the drive frequency f may satisfy the following expressions (5) and (6).

  In this case, since the impedance phase is not 0 and inductive when the drive frequency f satisfies Expression (5), the output of excessive current such as inrush current from the drive circuit to the power transmission coil side is suppressed. can do. Further, when the drive frequency f satisfies the formula (6), the power per time average supplied from the drive circuit to the power transmission coil side becomes positive, and there is no return of power to the drive circuit side, so that the drive circuit is configured. The load on the parts to be performed can be suppressed.

  Preferably, the power transmission device further includes a control circuit that controls the drive frequency, the power reception device further includes an output voltage detection circuit that detects a voltage across the load, and the load rectifies the AC power received by the power reception coil. A rectifier circuit; a variable load connected between output terminals of the rectifier circuit; a pseudo load composed of a switch element connected in parallel to the variable load and a resistance element connected in series to the switch element; The control circuit includes a frequency that minimizes a difference between a voltage value detected by the output voltage detection circuit when the switch element is on and a voltage value detected by the output voltage detection circuit when the switch element is off. You may perform the frequency search operation | movement which sets a drive frequency. In this case, the load resistance is changed by switching the switch element between the on state and the off state, and the distance between the power transmission device and the power reception device is searched by a frequency search operation for searching for a frequency at which the change in the voltage across the load is minimized. Even when the angle cannot fall within a desired range, the fluctuation of the voltage across the load can be minimized with respect to the load fluctuation by a simple and inexpensive means such as a switch element and a resistance element.

  Preferably, the power transmission device further includes a control circuit that controls the drive frequency, the power reception device further includes an output voltage detection circuit that detects a voltage across the load, and the load rectifies the AC power received by the power reception coil. A rectifier circuit; a variable load connected between output terminals of the rectifier circuit; a pseudo load composed of a switch element connected in parallel to the variable load and a resistance element connected in series to the switch element; The resistance element is 10Ω or less, and the control circuit may perform a frequency search operation for setting the drive frequency to a frequency at which the voltage value detected by the output voltage detection circuit becomes a maximum value when the switch element is on. . In this case, when the switch element of the pseudo load is turned on, the output voltage detection circuit can be used even when the load is small (when the equivalent resistance value of the load is large) or when the separation distance between the transmitting and receiving coils is large and the magnetic coupling is weak. Can detect the maximum value of the voltage at both ends of the load, and the frequency corresponding to the maximum value is substantially the same as the frequency at which the change in the voltage at both ends of the load is minimized with respect to the load fluctuation. Therefore, if power transmission is performed after setting the frequency corresponding to the maximum value to the frequency of the drive circuit and returning the switch element to the off state (cut-off state), the fluctuation of the voltage across the load is suppressed against the load fluctuation. can do.

  Preferably, the power transmission device further includes a high voltage high power power source and a low voltage low power power source, and the drive circuit converts a DC voltage supplied from the high voltage high power power source or the low voltage low power power source into an AC voltage, The high-voltage, high-power power supply may stop supplying DC voltage to the drive circuit during the frequency search operation. In this case, unnecessary radiation leaking from the power transmission device during the frequency search operation can be suppressed to a low level by performing the frequency search operation with the low-voltage low-power power source while the output of the high-voltage high-power power source is stopped.

  Preferably, a position adjustment unit that moves the position of the power transmission coil or the power reception coil is further provided, and the position adjustment unit may move the position of the power transmission coil or the power reception coil so that the drive frequency becomes the highest. In this case, since the relative displacement between the power transmission coil and the power reception coil can be reduced, the change in the voltage at both ends of the load with respect to load fluctuations can be maintained with low unnecessary radiation while maintaining high power transmission efficiency. Stable power supply can be realized.

  ADVANTAGE OF THE INVENTION According to this invention, the wireless power transmission system which suppressed the fluctuation | variation of the both-ends voltage of a load with respect to the fluctuation | variation of the equivalent resistance of a load is realizable.

1 is a configuration diagram illustrating a wireless power transmission system according to a first embodiment of the present invention. It is a graph which shows the frequency with which the variation | change_quantity with respect to the load fluctuation | variation of the both-ends voltage of load becomes the minimum with respect to the relative separation distance of a power transmission coil and a receiving coil. It is a graph which shows the various characteristics with respect to the drive frequency of the wireless power transmission system which concerns on 1st Embodiment of this invention. It is a block diagram which shows the wireless power transmission system which concerns on 2nd Embodiment of this invention. It is a flowchart which shows the frequency search operation | movement of the wireless power transmission system which concerns on 2nd Embodiment of this invention. It is a block diagram which shows the wireless power transmission system which concerns on the 3rd Embodiment of this invention. It is a flowchart which shows the frequency search operation | movement of the wireless power transmission system which concerns on the 3rd Embodiment of this invention. It is a graph which shows the frequency characteristic of the both-ends voltage of load with respect to the equivalent resistance value of load. It is a graph which shows the frequency characteristic of the imaginary part of the impedance of the wireless power transmission network comprised with the power transmission side resonance circuit with respect to the equivalent resistance value of load, a power reception side resonance circuit, and load. It is a graph which shows the maximum value of the equivalent resistance value of the load with which the both-ends voltage of the load with respect to the change of the coupling coefficient between power transmission / reception coils has the maximum point in the frequency region P vicinity. It is a block diagram which shows the wireless power transmission system which concerns on the 4th Embodiment of this invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

(First embodiment)
First, the configuration of the first embodiment of the present invention will be described. FIG. 1 is a configuration diagram illustrating a wireless power transmission system according to a first embodiment of the present invention.

  As shown in FIG. 1, the wireless power transmission system S <b> 1 includes a power transmission device 100 and a power reception device 200. In this wireless power transmission system S <b> 1, power is transmitted wirelessly from the power transmission device 100 to the power reception device 200. Here, the wireless power transmission system S1 will be described using an example in which the wireless power transmission system S1 is applied to a power supply facility for a moving body such as an electric vehicle.

  The power transmission device 100 includes a power supply circuit 110, a drive circuit 120, and a power transmission side resonance circuit 130. The power receiving device 200 includes a power receiving side resonance circuit 230 and a load 220.

  The power supply circuit 110 supplies DC power to the drive circuit 120. The power supply circuit 110 is not particularly limited as long as it outputs DC power. For example, a power factor correction (PFC) circuit that improves power factor, a switching power supply such as a switching converter, a high-voltage storage battery, For example, a voltage variable power source may be used. In the present embodiment, the power supply circuit 110 is connected to the commercial power supply 180 and functions as an AC-DC power supply that converts input AC power into desired DC power.

  The drive circuit 120 converts the DC power supplied from the power supply circuit 110 into AC power. The drive circuit 120 includes a switching circuit in which a plurality of switching elements are bridge-connected. The drive circuit 120 supplies an alternating current at a drive frequency to a power transmission side resonance circuit 130 described later.

The power transmission side resonance circuit 130 includes a power transmission coil L1 and a power transmission side capacitor unit C1. Specifically, the power transmission side resonance circuit 130 constitutes an LC resonance circuit formed by the power transmission coil L1 and the power transmission side capacitor unit C1. By setting the resonance frequency f _TX of this LC resonance circuit close to the resonance frequency f _RX of the power receiving side resonance circuit 230 described later, magnetic field resonance type power transmission is realized. In addition, as shown in this embodiment, the reactor Ls may be inserted in series with the power transmission side capacitor | condenser part C1. In this case, it becomes easy to control the imaginary part of the impedance of the wireless power transmission network including the power transmission side resonance circuit 130, the power reception side resonance circuit 230 described later, and the load 220 described later to be positive. Further, reactor Ls becomes a high impedance with respect to high enough frequency components than the resonance frequency f _TX, and thus serve as a filter for supplying power a high frequency component is removed to the power transmission coil L1.

  The power transmission coil L1 is formed by winding a litz wire such as copper or aluminum. The number of windings is appropriately set based on a separation distance between the power transmission coil L1 and a power reception coil L2 described later and a desired power transmission efficiency. In the power transmission coil L1, an alternating current flows at the driving frequency due to the alternating voltage of the driving frequency output from the driving circuit 120, and an alternating magnetic field is generated. That is, AC power is transmitted toward the power receiving coil L2 described later by this AC magnetic field. When the wireless power transmission system S1 of this embodiment is used in a power supply facility for a vehicle such as an electric vehicle, the power transmission coil L1 is disposed in the ground or in the vicinity of the ground.

  The power transmission side capacitor unit C1 forms a power transmission side resonance circuit 130 together with the power transmission coil L1. The power transmission side capacitor unit C1 has a function of adjusting the drive frequency and the voltage across the load 220. In this embodiment, although the power transmission side capacitor | condenser part C1 is comprised with the capacitor | condenser C11 connected in series with the power transmission coil L1, and the capacitor | condenser C12 connected in parallel, it is not restricted to this. For example, only the capacitor C11 connected in series to the power transmission coil L1 may be used.

The power receiving side resonance circuit 230 includes a power receiving coil L2 and a power receiving side capacitor unit C2. Specifically, the power reception side resonance circuit 230 constitutes an LC resonance circuit formed by the power reception coil L2 and the power reception side capacitor unit C2. By setting the resonance frequency f _RX of the LC resonance circuit close to the resonance frequency f _TX of the power transmission side resonance circuit 130, magnetic field resonance type power transmission is realized. As shown in the present embodiment, a reactor Lr may be inserted in series in the power receiving side capacitor unit C2. The reactor Lr has a high impedance with respect to a frequency component sufficiently higher than the resonance frequency f _RX , and serves as a filter that supplies electric power from which a high frequency component has been removed to a load 220 described later.

  The power receiving coil L2 is configured to receive power from the power transmitting coil L1, and is formed by winding a litz wire such as copper or aluminum. The number of turns is appropriately set based on the separation distance between the power transmission coil L1 and the power reception coil L2 and the desired power transmission efficiency. When the wireless power transmission system S1 of the present embodiment is used for a power supply facility for a vehicle such as an electric vehicle, the power receiving coil L2 is mounted on the lower portion of the vehicle or in the vicinity thereof.

  The power receiving side capacitor unit C2 forms a power receiving side resonance circuit 230 together with the power receiving coil L2. The power receiving side capacitor unit C <b> 2 has a function of adjusting the drive frequency and the voltage across the load 220. In the present embodiment, the power receiving side capacitor unit C2 includes the capacitor C22 connected in parallel to the power receiving coil L2 and the capacitor C21 connected in series, but is not limited thereto. For example, only the capacitor C21 connected in series to the power receiving coil L2 may be used.

  Here, in the present embodiment, the power transmission coil L1 and the power reception coil L2 are arranged at a distance G (cm) away from each other in the opposing direction (Z-axis direction in the drawing) of the power transmission coil L1 and the power reception coil L2, and the power transmission coil L1 In the direction orthogonal to the facing direction of the power receiving coil L2 (the X-axis direction in the drawing), the distance between the center points of the coils is arranged at a distance L (cm). Between the power transmission coil L1 and the power reception coil L2, there exists a coupling coefficient given by the equation k = M / √ (self inductance of the power transmission coil L1 × self inductance of the power reception coil L2). M is a mutual inductance defined by the amount of magnetic flux generated from the power transmission coil L1 linked to the power reception coil L2 by the high-frequency current fed from the drive circuit 120 to the power transmission coil L1. That is, the coupling coefficient k between the power transmission coil L1 and the power reception coil L2 is correlated with the distance G (cm) in the Z-axis direction and the distance L (cm) in the X-axis direction, and the distance G ( cm) is the smallest when the distance L (cm) in the X-axis direction is 0, and the largest when the distance G (cm) in the Z-axis direction is large and the distance L (cm) in the X-axis direction is large. Get smaller. Note that the Y-axis direction perpendicular to the X-axis direction also exhibits the same properties as those in the X-axis direction, and a description thereof is omitted here.

  The load 220 includes a rectifier circuit 210 and a variable load Vload. The load 220 stores or consumes AC power received by the power receiving coil L2.

  The rectifier circuit 210 has a function of rectifying the AC power received by the power receiving coil L2. Specifically, the rectifier circuit 210 converts AC power received by the power receiving coil L2 into DC power and supplies it to the variable load Vload. Examples of the rectifier circuit 210 include a half-wave rectifier circuit composed of a single switching element or a diode and a smoothing capacitor, a full-wave rectifier circuit composed of a bridge-connected four-element switching element or a diode and a smoothing capacitor, and the like. It is done.

  The variable load Vload is connected between the output terminals of the rectifier circuit 210, and stores or consumes power converted from AC power to DC power by the rectifier circuit 210. Examples of the variable load Vload include a resistor, an electronic load, an electric device such as an electric motor, a secondary battery, a battery charger for charging the secondary battery, and the like. The variable load Vload can be regarded as a resistive load in which the equivalent resistance value of the load changes with time depending on the power demand state (storage state or consumption state). Since the power consumption in the rectifier circuit 210 is sufficiently smaller than the power consumption in the variable load Vload, the equivalent resistance value of the load 220 may be regarded as the equivalent resistance value of the variable load Vload.

  Here, the F matrix of the four-terminal network composed of the power transmission side resonance circuit 130 and the power reception side resonance circuit 230 is expressed by Equation (1), the real part of A of the F matrix is Ra, the imaginary part is Xa, and the F matrix The real part of B is Rb, the imaginary part is Xb, and two terminals constituted by the power transmission side resonance circuit 130, the power reception side resonance circuit 230, and the load 220 when the power transmission side resonance circuit is viewed from the output side of the drive circuit 120. The imaginary part of the impedance Z of the network is X, the change of the imaginary part X of the impedance Z with respect to the frequency f of the AC power of the drive circuit 120 is δX, and the equivalent resistance when the load 220 is a load of an arbitrary size is RL0. The circuit constants of the four-terminal network are determined so that A and B of the F matrix satisfy the following expressions (2), (3), and (4). Note that A and B of the F matrix are determined by the resistance value, the capacitance value, the inductance value, and the drive frequency of the circuit components that constitute the four-terminal circuit network. The upper and lower limits of the drive frequency are not particularly limited, but when the coupling coefficient k between the power transmission coil L1 and the power reception coil L2 is the maximum determined by the specification, that is, between the center points of the power transmission coil L1 and the power reception coil L2. When the driving frequency of the selected driving circuit 120 is the upper limit value when the distance of the power is the minimum determined by the specification, the coupling coefficient k between the power transmission coil L1 and the power receiving coil L2 is the minimum determined by the specification That is, the drive frequency of the drive circuit 120 selected when the distance between the center points of the power transmission coil L1 and the power reception coil L2 is the maximum determined by the specification may be set as the lower limit value.

（但し、ｊ^２＝−１である。）

(However, j ² = −1.)

  More preferably, the four-terminal network is such that A and B of the F matrix satisfy the expressions (2), (3), and (4), and the drive frequency satisfies the following expressions (5) and (6): Circuit constants are determined.

  Here, the reason that the change in the voltage across the load can be reduced to ± 10% or less even if the equivalent resistance value of the load changes by satisfying the expressions (2), (3), and (4) of A and B of the F matrix Will be described in detail.

  When the input voltage of the power transmission side resonance circuit 130 is Vi, the input current is Ii, the voltage across the load 220 (output voltage) is Vo, and the current flowing into the load 220 (output current) is Io, an F matrix of a four-terminal network. (1) and the relationship between the input voltage Vi, the input current Ii, the output voltage Vo, and the output current Io are expressed by the following expressions (7) to (9).

  Here, the load 220 is a load of an arbitrary size, and the equivalent resistance is represented by RL0. Since the load 220 is connected between the output terminals of the power receiving side resonance circuit 230, the output voltage Vo and the output current Io And the equivalent resistance RL0 of the load 220, the relationship of the following formula (10) is established.

  Substituting this equation (10) into equations (8) and (9) yields the following equation (11).

  Here, the condition that the change in the output voltage Vo becomes 0 with respect to the change in the equivalent resistance RL0 of the load 220 is expressed by the following equation (12).

  Therefore, in order for equation (12) to always hold, B = 0 must be satisfied. In general, B is a complex number B = Rb + jXb represented by a real part Rb and an imaginary part Xb. The real part Rb and the imaginary part Xb are a resistance value, a capacitance value, an inductance value, and a circuit component constituting a four-terminal network. It depends on the driving frequency. However, when the Q values (described later) of the power transmission coil L1 and the power reception coil L2 are very high, Rb≈0, so that the circuit constant of the four-terminal network that substantially satisfies the imaginary part Xb = 0 of B. To the problem of seeking Therefore, in the wireless power transmission system S1, when the circuit constant of the four-terminal network is set so that the driving frequency satisfies the imaginary part Xb = 0 of B in Formula (1) of the F-matrix of the four-terminal network, the load 220 Even if the value of the equivalent resistance RL0 changes, the change in the voltage Vo across the load 220 can be minimized.

  The change δVo of the voltage Vo at both ends of the load 220 due to the load fluctuation is preferably as small as possible. However, when the variable load Vload as a component of the load 220 is a power supply circuit such as a battery charger, the input voltage fluctuation of the power supply circuit is generally In general, it is allowed up to a range of ± 10%. Therefore, when the equivalent resistance RL0 of the load 220 at an arbitrary load is substituted into the expression (11), the voltage Vo (RL0) across the load 220 and the equivalent resistance RL of the load 220 different from the equivalent resistance RL0 are expressed by the expressions ( 11), the difference from the both-ends voltage Vo (RL) of the load 220 when substituted into 11) is defined as a change δVo of the both-ends voltage Vo of the load 220 when the equivalent resistance of the load 220 changes from RL0 to RL. When the ratio δVo / Vo of the change δVo of the voltage 220 across the load 220 to the voltage Vo (RL0) across the load 220 when the resistance is RL0 is calculated, the following equation (13) is obtained.

  Here, Ra and Xa in Formula (13) are the real part and imaginary part of A in F matrix formula (1), and Rb and Xb are the real part and imaginary part of B in F matrix formula (1). It is. The real part Ra and the imaginary part Xa of A and the real part Rb and the imaginary part Xb of B are determined by the resistance value, the capacitance value, the inductance value, and the drive frequency of the circuit components constituting the four-terminal network. Further, the equivalent resistance RL0 of the load 220 at an arbitrary load is set as a load when the demand power of the load becomes maximum, and the equivalent resistance RL of the load 220 different from the equivalent resistance RL0 is set as the case where the demand power of the load is minimum. Assuming that the load is the load, the equivalent resistance RL when the demand power of the load is the minimum is an infinite value, so the δVo / Vo is the maximum, as shown in the following formula (14).

  Further, in the equation (13), when RL> RL0, the ratio δVo / Vo of the change δVo of the voltage 220 across the load 220 to the voltage Vo (RL0) across the load 220 when the equivalent resistance of the load 220 is RL0 is always positive. Therefore, the condition to be satisfied by the imaginary part Xb of B in the F matrix formula (1) in which the δVo / Vo is 10% or less is the formula (14) ≦ 0.1, and the following formula (15) It becomes like this. Also, the discriminant D on the left side of the equation (15) is as the following equation (16).

From the equation (15), the condition to be satisfied by the imaginary part Xb of B in the F matrix equation (1) in which the ratio δVo / Vo of the voltage across the load 220 is 10% or less is the value on the left side of the equation (15). Therefore, the real number range of the imaginary part Xb in which is always 0 or negative is obtained. Here, in order to make the imaginary part Xb a real number, the discriminant D in the equation (16) should always be 0 or positive. In addition, since the circuit Q value of the four-terminal network of the wireless power transmission system that wirelessly and efficiently transmits power from the power transmission side to the power reception side is very large (the power transmission coil L1 of the power transmission side resonance circuit, the power transmission side capacitor unit C1). Since the equivalent series resistance ESR of the power receiving coil L2 and the power receiving side capacitor C2 of the power receiving side resonance circuit is sufficiently small), (Xa / Ra) ² is (Xa / Ra) ² ≈0. Therefore, when the condition that the discriminant D in Expression (16) is 0 or positive and the condition that (Xa / Ra) ² ≈0 are applied to Expression (15) and Expression (16), the drive frequency during actual operation , The equivalent resistance RL0 of the load 220 at an arbitrary load is in the range of the equation (2), and the imaginary part Xb of B in the equation (1) of the F matrix represents the equations (3) and (4). If the circuit constants of the four-terminal network are set so as to satisfy, the change in the voltage Vo across the load 220 can be suppressed to 10% or less even if the load value changes.

  In Equation (13), the equivalent resistance RL0 of the load 220 at an arbitrary load is a load when the load demand power is minimum, and the equivalent resistance RL of the load 220 different from the equivalent resistance RL0 is the demand for the load. Assuming that the load is when the power is maximum, the ratio δVo / Vo of the change δVo of the voltage 220 across the load 220 to the voltage Vo (RL0) across the load 220 when the equivalent resistance of the load 220 is RL0 is always negative, and δVo The condition satisfying /Vo≧−0.1 was a range wider than the range represented by the formulas (2), (3), and (4). Therefore, even when the load is suddenly heavy (the equivalent resistance RL0 of the load 220 becomes small) or light (the equivalent resistance RL0 of the load 220 becomes large) when operating with an arbitrary load, the F matrix When the circuit constants of the four-terminal network represented by Expression (1) are set so as to satisfy Expressions (2), (3), and (4), the voltage Vo across the load 220 when the equivalent resistance of the load 220 is RL0. The ratio δVo / Vo of the change δVo of the voltage Vo across the load 220 with respect to (RL0) can be within ± 10%.

  As described above, the wireless power transmission system S1 according to the present embodiment includes the A and B of the F matrix of the four-terminal network composed of the power transmission side resonance circuit 130 and the power reception side resonance circuit 230 of the wireless power transmission system S1. However, since the four-terminal network is configured to satisfy the expressions (2), (3), and (4), the change in the voltage across the load 220 can be suppressed to ± 10% or less even when the load fluctuates. . Specifically, when the load 220 is a power supply circuit such as a battery charger, the allowable input voltage range of the power supply circuit is normally defined as ± 10%, and input of a voltage exceeding the range is a component constituting the power supply circuit. There is a risk that a high load is applied to or stopped. In the wireless power transmission system S1 according to the present embodiment, even if the equivalent resistance of the power supply circuit that is the load 220 varies, the fluctuation of the input voltage of the power supply circuit that is the load 220 is within the allowable input voltage range of ± 10%. The following can be suppressed. That is, the fluctuation of the voltage across the load 220 can be suppressed with respect to the fluctuation of the equivalent resistance of the load 220.

  In the wireless power transmission system S1 according to the present embodiment, the driving frequency is f, the change in the driving frequency f is δf, and the wireless power transmission is configured by the power transmission side resonance circuit 130, the power reception side resonance circuit 230, and the load 220. If the imaginary part of the impedance Z of the mesh is X and the change of the imaginary part X with respect to the driving frequency f is δX, the driving frequency f satisfies Expressions (5) and (6). Therefore, when the drive frequency f satisfies the formula (5), the phase of the impedance Z is not 0 and is inductive, so that an excessive current output such as an inrush current is output from the drive circuit to the power transmission coil L1 side. Can be suppressed. Further, when the drive frequency f satisfies the formula (6), the power per time average supplied from the drive circuit to the power transmission coil L1 side becomes positive, and there is no return of power to the drive circuit side. The load on the components to be configured can be suppressed.

  Here, the fact that the fluctuation of the voltage across the load 220 can be suppressed with respect to the fluctuation of the equivalent resistance of the load 220 according to the above-described embodiment will be described using a specific example.

The wireless power transmission system S1 according to the first embodiment is configured as follows. First, based on the specification of the allowable separation distance between the power transmission coil L1 and the power reception coil L2 and the power transmission efficiency, the inductance value of the power transmission coil L1 is 120 (μH), the inductance value of the power reception coil L2 is 126 (μH), and the reactor Ls The inductance value was 10 (μH), and the inductance value of the reactor Lr was 10 (μH). At this time, the coupling coefficient k between the power transmission coil L1 and the power reception coil L2 is 10 (cm) at a minimum in the distance G (cm) in the Z-axis direction and 0 (cm) in the distance L (cm) in the X-axis direction. It was 0.33. The Q value indicating the loss of the power transmission coil L1, the power receiving coil L2, the reactor Ls, and the reactor Lr is represented by Q = ωL / where L represents the inductance of each coil or each reactor, r represents its DC resistance component, and fq represents the frequency. represented by r. However, fq of ω = 2πfq is a value near the driving frequency. In this example, each Q value is 200. Further, since the Q value indicating the loss of the capacitors C11, C12, C21, C22 is sufficiently larger than the Q values of the power transmission coil L1, the power receiving coil L2, the reactor Ls, and the reactor Lr, the capacitors C11, C12, C21, C22 The loss was ignored. As the load 220, a full-wave rectifier circuit is used as the rectifier circuit 210, an electronic load is used as the variable load Vload, and the input voltage of the electronic load, which is the voltage across the load 220, is 245 (V) based on the specifications, and the maximum power 3 The minimum resistance value of the electronic load was 18 (Ω) so that .3 (kW) was obtained. Note that the power consumption in the rectifier circuit 210 is ignored because it can be regarded as relatively small when the power consumption in the variable load Vload is sufficiently large. That is, the equivalent resistance of the load 220 is that the voltage across the load 220 is 245 (V) and the power demand of the load 220 is the maximum power 3.3 (kW), so equivalent resistance = (voltage across the load) ² / load the basis of the power demand ^{relationship,} the 245 2/3300 = 18 (Ω ).

  Here, referring to FIG. 2, the driving frequency when the distance G (cm) in the Z-axis direction is at least 10 (cm) and the distance L (cm) in the X-axis direction is 0 (cm) is defined as the upper limit value. Explain why. FIG. 2 is a graph showing the frequency at which the change amount δVo with respect to the load fluctuation of the voltage across the load is the smallest with respect to the relative separation distance between the power transmission coil L1 and the power reception coil L2. In the graph shown in FIG. 2, the horizontal axis indicates the relative separation distance OFFSET (cm) in the X-axis direction or the Y-axis direction of the power transmitting coil L1 and the power receiving coil L2, and the vertical axis indicates the load fluctuation of the voltage Vo across the load 220. The frequency (kHz) at which the change amount δVo with respect to the smallest value is displayed. In the example shown in FIG. 2, the case where the relative separation distance of the power transmission coil L1 and the power reception coil L2 in the Z-axis direction is 8 cm, 10 cm, 13 cm, and 18 cm is displayed. As shown in FIG. 2, when the relative distance between the power transmission coil L1 and the power reception coil L2 is the shortest, it can be seen that the frequency at which the change amount δVo with respect to the load fluctuation of the voltage Vo at both ends of the load 220 is the smallest becomes a high value. . That is, when the relative distance between the power transmission coil L1 and the power reception coil L2 determined by a predetermined specification is the smallest, the frequency at which the change amount δVo with respect to the load fluctuation of the both-end voltage Vo of the load 220 is the smallest is the upper limit value of the drive frequency. As a result, even when the relative distance between the power transmission coil L1 and the power reception coil L2 changes, the frequency at which the change amount δVo with respect to the load fluctuation of the voltage Vo across the load 220 is reduced to a frequency lower than the upper limit value is found. It becomes possible.

  Subsequently, the output voltage of the drive circuit 120 is an effective value of 390 (V), the equivalent resistance RL0 of the load 220 is 18Ω, the drive frequency is 90 ± 0.125 (kHz), and the voltage Vo across the load 220 is Vo = A set of capacitors C11, C12, C21, and C22 in which the imaginary part Xb of B in Formula (1) of the F matrix satisfies Xb≈0 in the range of 245 ± 1 (V) was obtained, and the circuit characteristics at that time were obtained. The results are shown in Samples No. 1 to No. 5 in Table 1. In Table 1, δVo / Vo is the voltage across the load 220 when the equivalent resistance RL0 of the load 220 is changed from 18Ω to 18Ω + 1 kΩ with respect to the voltage Vo across the load 220 when the equivalent resistance RL0 of the load 220 is 18Ω. Represents the ratio of the voltage difference (change amount) δVo, and η (%) represents the power transmission efficiency between the power transmission side resonance circuit 130 and the power reception side resonance circuit 230. As shown in Table 1, in Sample No. 4 and Sample No. 5, the equivalent resistance RL0 of the load 220 does not satisfy Equation (2), and the imaginary part Xb (real value) of B in Equation (1) of the F matrix is an imaginary value. Since the equations (3) and (4) are not satisfied, the change of the voltage Vo across the load 220 with respect to the load fluctuation exceeds 10 (%), which is not suitable. On the other hand, in the samples No1 to No3, the equivalent resistance RL0 of the load 220 satisfies Expression (2), and the imaginary part Xb of B in Expression (1) of the F matrix satisfies Expressions (3) and (4). Therefore, the power transmission efficiency is high, and the change with respect to the load fluctuation of the voltage Vo between both ends of the load 220 can be suppressed to 10% or less. From the above, when the capacitors C11, C12, C21, and C22, which are circuit constants of the four-terminal network, are set to the values of the samples No1 to No3, fluctuations in the voltage Vo across the load 220 can be suppressed.

  Subsequently, the voltage Vo (V) across the load 220 with respect to the driving frequency, the imaginary part X (Ω) of the impedance Z, and the power transmission efficiency η (%) between the power transmission side resonance circuit 130 and the power reception side resonance circuit 230 are obtained. It was. The results are shown in FIG. FIG. 3 is a graph showing various characteristics with respect to the driving frequency of the wireless power transmission system according to the first embodiment of the present invention. The graph shown in FIG. 3 displays the drive frequency (kHz) on the horizontal axis, the voltage Vo (V) across the load 220 on the vertical axis (left side in the figure), and the power transmission side resonance circuit on the vertical axis (right side in the figure). The power transmission efficiency η (%) between 130 and the power receiving resonance circuit 230 and the imaginary part X (Ω) of the impedance Z are displayed. In this example, various characteristics with respect to the drive frequency when the coupling coefficient k between the power transmission coil L1 and the power reception coil L2 is 0.33 and the equivalent resistance of the load 220 is 18Ω are shown. As shown in FIG. 3, there are two drive frequencies at which the voltage Vo across the load 220 exhibits a maximum value. However, it is preferable to adopt the O point near the maximum point with the higher frequency as the drive frequency of the drive circuit 120. Of the drive frequencies at which the voltage Vo across the load 220 exhibits a maximum value, the lower frequency does not satisfy the equation (5), but the higher frequency satisfies the equations (5) and (6). Therefore, the output of excessive current such as inrush current from the drive circuit 120 to the power transmission coil L1 side can be suppressed and the drive circuit 120 to the power transmission coil L1 side. Since the supplied power per time average is positive and there is no return of power to the drive circuit 120 side, the load on the components constituting the drive circuit 120 can be suppressed.

(Second Embodiment)
Next, the configuration of the wireless power transmission system S2 according to the second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a configuration diagram illustrating a wireless power transmission system according to the second embodiment of the present invention.

  The wireless power transmission system S2 includes a power transmission device 100 and a power reception device 200, as in the first embodiment. In the wireless power transmission system S <b> 2, power is transmitted wirelessly from the power transmission device 100 to the power reception device 200. In the present embodiment, the power transmission device 100 includes a power supply circuit 111, a drive circuit 120, a power transmission side resonance circuit 130, and a control circuit 140. The power receiving device 200 includes a power receiving side resonance circuit 230, a load 221, an output voltage detection circuit 250, and a power receiving side control circuit 260. The configuration of the drive circuit 120, the power transmission side resonance circuit 130, and the power reception side resonance circuit 230 is the same as that of the wireless power transmission system S1 according to the first embodiment. That is, the wireless power transmission system S2 according to the second embodiment includes a power supply circuit 111 and a load 221 instead of the power supply circuit 110 and the load 220, a control circuit 140, an output voltage detection circuit 250, and a power receiving side control circuit. The second embodiment is different from the first embodiment in that 260 is provided. Hereinafter, a description will be given focusing on differences from the first embodiment.

  The power supply circuit 111 is connected to the commercial power supply 180, converts input AC power into DC power, and supplies the DC power to the drive circuit 120. In the present embodiment, the power supply circuit 111 includes a high voltage high power power supply 150 and a low voltage low power power supply 160. Specifically, the high voltage high power power supply 150 supplies a DC voltage of about 350 (V) to 430 (V) to the drive circuit 120, and the low voltage low power power supply 160 is 50 (V) to 150 (V). ) About DC voltage is supplied to the drive circuit 120. Therefore, in this embodiment, the drive circuit 120 converts the DC voltage supplied from the high-voltage high-power power supply 150 or the low-voltage low-power power supply 160 into an AC voltage. The high voltage high power power supply 150 has a high voltage output terminal T3 connected to the high voltage input terminal T5 of the drive circuit 120, and a GND terminal T4 connected to the low voltage input terminal T6 of the drive circuit 120. Further, the high-voltage high-power power supply 150 has a control terminal CNT1, and is configured such that an output can be switched between an on state and a high impedance state by a control circuit 140 described later. As the high-voltage high-power power supply 150 configured in this way, a power supply (power factor correction circuit built-in power supply) equipped with a PFC (Power Factor Correction) circuit is preferable. More preferably, a power supply equipped with a PFC circuit and capable of varying the output voltage in a range where the efficiency decrease is small is preferable. On the other hand, in the low voltage low power power supply 160, the high voltage output terminal T1 is connected to the high voltage input terminal T5 of the drive circuit 120 via the diode D1, and the GND terminal T2 is connected to the low voltage input terminal T6 of the drive circuit 120. Specifically, the anode of the diode D1 is connected to the high voltage output terminal T1 of the low voltage low power source 160, the cathode of the diode D1 is connected to the high voltage input terminal T5 of the drive circuit 120, and the high voltage input terminal T5 of the drive circuit 120 is connected. Is prevented from flowing into the high-voltage output terminal T1 of the low-voltage low-power power supply 160. The low-voltage low-power power supply 160 has a control terminal CNT2, and is configured such that an output can be switched between an on state and a high impedance state by a control circuit 140 described later. An example of the low-voltage low-power power supply 160 configured in this way is a switching power supply.

  The control circuit 140 has a function of controlling the drive frequency of the alternating current supplied from the drive circuit 120 to the power transmission side resonance circuit 130. That is, the control circuit 140 is configured to perform a frequency search operation for the drive frequency. A specific frequency search operation will be described later. The control circuit 140 also has a function of switching the outputs of the high voltage high power power supply 150 and the low voltage low power power supply 160. In the present embodiment, the control circuit 140 controls to stop the supply of the DC voltage from the high voltage high power power supply 150 to the drive circuit 120 during the frequency search operation of the drive frequency. That is, during the frequency search operation of the drive frequency, the control circuit 140 outputs a signal to the control terminal CNT1 so that the output of the high voltage high power source 150 is in a high impedance state, and the output of the low voltage low power source 160 is A signal is output to the control terminal CNT2 so as to be turned on. Thus, by performing the frequency search operation by the low voltage low power power supply 160 with the output of the high voltage high power power supply 150 stopped, unnecessary radiation leaking from the power transmission device 100 during the frequency search operation can be suppressed to a low level. . Further, the control circuit 140 transmits an instruction to turn on or off a switch element SW of a load 221 described later to a power receiving side control circuit 260 described later via a communication unit (not shown).

  The load 221 includes a rectifier circuit 210, a variable load Vload, and a pseudo load 240. The rectifier circuit 210 has a function of rectifying the AC power received by the power receiving coil L2 as in the first embodiment. The variable load Vload is connected between the output terminals of the rectifier circuit 210 as in the first embodiment, and stores or consumes the power converted from AC power to DC power by the rectifier circuit 210. The pseudo load 240 has a function of changing the equivalent resistance value of the load 221. Specifically, the pseudo load 240 includes a switch element SW and a resistance element Rd, and is connected in parallel to the variable load Vload. The switch element SW plays a role of switching connection / disconnection of the resistance element Rd to the variable load Vload. The resistance element Rd is connected in series with the switch element SW. The pseudo load 240 configured as described above changes the equivalent resistance value of the load 221 by switching the ON state and the OFF state of the switch element SW by the power receiving side control circuit 260 described later.

  The output voltage detection circuit 250 detects the voltage across the load 221. Specifically, the output voltage detection circuit 250 is connected between the rectifier circuit 210 and the variable load Vload, and detects the output voltage value of the rectifier circuit 210. That is, the output voltage value of the rectifier circuit 210 corresponds to the voltage value across the load 221. Examples of the output voltage detection circuit 250 include a voltage dividing circuit and a voltage detection transformer. The voltage value detected by the output voltage detection circuit 250 is output as a voltage detection signal to the power receiving side control circuit 260 described later.

  The power receiving side control circuit 260 has a function of switching the on state and the off state of the switch element SW of the pseudo load 240 based on an instruction from the control circuit 140. The power receiving side control circuit 260 also has a function of transmitting the voltage value received from the output voltage detection circuit 250 to the control circuit 140 via communication means (not shown).

  Next, the frequency search operation of the wireless power transmission system S2 according to the second embodiment of the present invention will be described in detail with reference to the flowchart of FIG. FIG. 5 is a flowchart illustrating a frequency search operation of the wireless power transmission system according to the second embodiment of the present invention.

  Here, the frequency search operation performed by the control circuit 140 means that the drive frequency of the drive circuit 120 is changed within a predetermined frequency range, and the voltage detection signal output from the output voltage detection circuit 250 is changed to the ON state of the switch element SW. The frequency characteristic data for the drive frequency of the drive circuit 120 in both of the off states is stored in the memory, and the frequency characteristic data when the switch element SW is in the on state and the frequency characteristic data when the switch element SW is in the off state. In comparison, the frequency that minimizes the voltage difference between the two frequency characteristic data is selected. Hereinafter, the frequency search operation will be described in detail.

  First, the control circuit 140 clears all the memories related to the search, and sets the drive frequency of the drive circuit 120 to the upper limit frequency in the frequency range (predetermined frequency range) to be searched (setting of the initial frequency). (Step S100)

  Subsequently, the control circuit 140 turns off the high-voltage high-power power supply 150 and turns on the low-voltage low-power power supply 160 among the two types of power supplies that constitute the power supply circuit 111. That is, the control circuit 140 outputs a signal to the control terminal CNT1 so that the output of the high-voltage high-power power supply 150 is in a high impedance state, and outputs a signal to the control terminal CNT2 so that the output of the low-voltage low-power power supply 160 is turned on. Is output. Thereby, a low initial voltage (about 50 V to 150 V) is supplied from the power supply circuit 111 to the drive circuit 120. (Step S101)

  Subsequently, the control circuit 140 transmits an instruction to turn on the switch element SW of the pseudo load 240 to the power receiving side control circuit 260 via the communication unit. The power receiving side control circuit 260 turns on the switch element SW of the pseudo load 240 based on an instruction from the control circuit 140. As a result, the resistance element Rd is connected in parallel to the variable load Vload, and the equivalent resistance value of the load 221 is temporarily low. In this state, the drive circuit 120 is operated to supply an alternating current to the power transmission side resonance circuit 130. (Step S102)

  When AC current is supplied from the drive circuit 120 to the power transmission side resonance circuit 130, the power transmission coil L1 generates an AC magnetic field based on the AC current, and the power receiving coil L2 receives AC power via the AC magnetic field. Then, the rectifier circuit 210 converts AC power received by the power receiving coil L2 into DC power and supplies it to the variable load Vload. At this time, the output voltage detection circuit 250 detects the output voltage value of the rectifier circuit 210 and outputs it to the power receiving side control circuit 260 as a voltage detection signal. The power receiving side control circuit 260 transmits the voltage value detected by the output voltage detection circuit 250 to the control circuit 140 via the communication means. (Step S103)

  Subsequently, the control circuit 140 stores the combination of the voltage value and the initial frequency transmitted from the power receiving side control circuit 260 in step S103 in the first search memory in the control circuit 140 as array data. (Step S104)

  Subsequently, the control circuit 140 changes the driving frequency of the driving circuit 120 from the initial frequency to a lower frequency in the frequency range for searching, and drives the driving circuit 120. (Step S105) The output voltage value of the rectifier circuit 210 at this time is detected by the output voltage detection circuit 250, and is output to the power receiving side control circuit 260 as a voltage detection signal. The power receiving side control circuit 260 transmits the voltage value detected by the output voltage detection circuit 250 to the control circuit 140 via the communication means. (Step S106) Then, the control circuit 140 uses the combination of the voltage value transmitted from the power receiving side control circuit 260 in step S106 and the changed frequency as array data in the first search memory in the control circuit 140. Store additional in order. (Step S107)

  Subsequently, the output voltage value of the rectifier circuit 210 having the second array element number from the tail stored in the first search memory of the control circuit 140 is compared with the output voltage value of the rectifier circuit 210 acquired in step S107. (Step S108), when the output voltage value of the rectifier circuit 210 acquired in Step S107 is equal to or lower than the output voltage value of the rectifier circuit 210 of the second array number from the last stored in the first search memory And the last array element number is stored in the storage memory in the control circuit 140 (step S108Y). When the output voltage value of the rectifier circuit 210 acquired in step S107 is larger than the output voltage value of the rectifier circuit 210 having the second array element number from the tail stored in the first search memory (step S108N), The frequency to be changed is compared with the lower limit frequency in the frequency range to be searched (step S109). When the frequency to be changed reaches the lower limit frequency in the frequency range to be searched, the processing operation is stopped and the last array number is controlled. The data is stored in the storage memory in the circuit 140 (step S109Y). On the other hand, when the frequency to be changed has not reached the lower limit frequency in the frequency range to be searched (step S109N), the processing operations from step S105 to step S109 are repeatedly executed.

  Subsequently, in step S108Y or step S109Y, the control circuit 140 resets (resets the initial frequency) to the upper limit frequency in the frequency range (predetermined frequency range) in which the drive frequency of the drive circuit 120 is searched. . (Step S110)

  Subsequently, the control circuit 140 transmits an instruction to turn off the switch element SW of the pseudo load 240 to the power receiving side control circuit 260 via the communication unit. The power receiving side control circuit 260 turns off the switch element SW of the pseudo load 240 based on an instruction from the control circuit 140. Thereby, the resistance element Rd is disconnected from the variable load Vload, and the equivalent resistance value of the load 221 returns to a high state. In this state, the drive circuit 120 is operated to supply an alternating current to the power transmission side resonance circuit 130. (Step S111)

  Subsequently, when AC current is supplied from the drive circuit 120 to the power transmission side resonance circuit 130, the power transmission coil L1 generates an AC magnetic field based on the AC current, and the power receiving coil L2 receives AC power via the AC magnetic field. . Then, the rectifier circuit 210 converts AC power received by the power receiving coil L2 into DC power and supplies it to the variable load Vload. At this time, the output voltage detection circuit 250 detects the output voltage value of the rectifier circuit 210 and outputs it to the power receiving side control circuit 260 as a voltage detection signal. The power receiving side control circuit 260 transmits the voltage value detected by the output voltage detection circuit 250 to the control circuit 140 via the communication means. (Step S112)

  Subsequently, the control circuit 140 stores the set of the voltage value and the initial frequency transmitted from the power receiving side control circuit 260 in step S112 in the second search memory in the control circuit 140 as array data. (Step S113)

  Subsequently, the control circuit 140 changes the driving frequency of the driving circuit 120 from the initial frequency to a lower frequency in the frequency range for searching, and drives the driving circuit 120. (Step S114) The output voltage value of the rectifier circuit 210 at this time is detected by the output voltage detection circuit 250 and output to the power receiving side control circuit 260 as a voltage detection signal. The power receiving side control circuit 260 transmits the voltage value detected by the output voltage detection circuit 250 to the control circuit 140 via the communication means. (Step S115) Then, the control circuit 140 uses the combination of the voltage value transmitted from the power receiving side control circuit 260 in step S115 and the changed frequency as array data in the second search memory in the control circuit 140. Store additional in order. (Step S116)

  Subsequently, the array element number stored in the second search memory and the last array element number stored in the storage memory of the control circuit 140 are compared (step S117) and stored in the second search memory. If the array element number does not match the last array element stored in the storage memory of the control circuit 140 (step S117N), the array element number stored in the second search memory is stored in the storage memory of the control circuit 140. Steps S114 to S117 are repeatedly executed until the stored last array element number is reached. On the other hand, when the array element number stored in the second search memory matches the last array element number stored in the storage memory of the control circuit 140 (step S117Y), the control circuit 140 causes the first search element to be searched. The output voltage value and frequency array data of the rectifier circuit 210 stored in the memory and the output voltage value and frequency array data of the rectifier circuit 210 stored in the second search memory are compared, and the first The frequency that minimizes the difference between the output voltage value of the rectifier circuit 210 stored in the search memory and the output voltage value of the rectifier circuit 210 stored in the second search memory is searched. (Step S118)

  Subsequently, the control circuit 140 stores the frequency at which the difference between the output voltage values of the rectifier circuit 210 searched in step S118 is the smallest in the setting memory in the control circuit 140. (Step S119)

  Then, the control circuit 140 sets the frequency stored in the setting memory to the drive frequency of the drive circuit 120. Thus, when the drive frequency of the drive circuit 120 is set to the frequency stored in the setting memory, the frequency search operation ends. (Step S120) As described above, the frequency search operation performed by the control circuit 140 is the voltage value detected by the output voltage detection circuit 250 when the switch element SW is on and the output when the switch element SW is off. The drive frequency is set to a frequency at which the difference between the voltage values detected by the voltage detection circuit 250 is minimized.

  When the frequency search operation is finished and the control circuit 140 sets the frequency stored in the setting memory as the drive frequency of the drive circuit 120, the control circuit 140 is the high power source among the two types of power supplies constituting the power supply circuit 111. The high voltage power source 150 is turned on, and the low voltage low power source 160 is turned off. That is, the control circuit 140 outputs a signal to the control terminal CNT1 so that the output of the high voltage high power source 150 is turned on, and outputs a signal to the control terminal CNT2 so that the output of the low voltage low power source 160 is in a high impedance state. Is output. As a result, in the wireless power transmission system S2, the voltage across the load 221 (the output voltage of the rectifier circuit 210) is boosted to a desired voltage value, and the voltage across the load 221 is unlikely to change due to load fluctuations. It becomes possible to transmit electric power.

  As described above, in the wireless power transmission system S2 according to the present embodiment, the power transmission device 100 further includes the control circuit 140 that controls the drive frequency, and the power reception device 200 detects the output voltage across the load 221. The circuit 250 further includes a load 221 that rectifies the AC power received by the power receiving coil L2, a variable load Vload connected between the output terminals of the rectifier circuit 210, and the variable load Vload in parallel. The control circuit 140 includes an output voltage detection circuit 250 when the switch element SW is in an ON state. The pseudo load 240 includes a switch element SW connected and a resistance element Rd connected in series to the switch element SW. The difference between the voltage value detected by the output voltage detection circuit 250 and the voltage value detected by the output voltage detection circuit 250 when the switch element SW is in the OFF state is the largest. And performing frequency search operation for setting the driving frequency to a frequency at which. Therefore, by changing the load resistance by switching the switch element SW between the on state and the off state, the frequency search operation for searching for the frequency at which the change in the voltage across the load 221 is minimized, Even when the distance or angle cannot be within the desired range, the fluctuation of the voltage across the load 221 can be minimized with respect to the load fluctuation by a simple and inexpensive means such as the switch element SW and the resistance element Rd. it can.

  In the wireless power transmission system S2 according to the present embodiment, the power transmission device 100 further includes a high voltage high power power source 150 and a low voltage low power power source 160, and the drive circuit 120 includes the high voltage high power power source 150 or a low power source. The DC voltage supplied from the low voltage power source 160 is converted into an AC voltage, and the high voltage high power source 150 stops supplying the DC voltage to the drive circuit 120 during the frequency search operation. Therefore, unnecessary radiation leaking from the power transmission device 100 during the frequency search operation can be suppressed to a low level by performing the frequency search operation by the low-voltage low-power power supply 160 in a state where the output of the high-voltage high-power power supply 150 is stopped.

(Third embodiment)
Next, the configuration of the wireless power transmission system S3 according to the third embodiment of the present invention will be described with reference to FIG. FIG. 6 is a configuration diagram showing a wireless power transmission system according to the third embodiment of the present invention.

  The wireless power transmission system S3 includes a power transmission device 100 and a power reception device 200, as in the first embodiment. In the wireless power transmission system S <b> 3, power is transmitted wirelessly from the power transmission device 100 to the power reception device 200. In the present embodiment, the power transmission device 100 includes a power supply circuit 111, a drive circuit 120, a power transmission resonance circuit 130, and a control circuit 141. The power receiving device 200 includes a power receiving side resonance circuit 230, a load 222, an output voltage detection circuit 250, and a power receiving side control circuit 260. The configuration of the drive circuit 120, the power transmission side resonance circuit 130, and the power reception side resonance circuit 230 is the same as that of the wireless power transmission system S1 according to the first embodiment. That is, the wireless power transmission system S3 according to the third embodiment includes a power supply circuit 111 and a load 222 instead of the power supply circuit 110 and the load 220, a control circuit 141, an output voltage detection circuit 250, and a power receiving side control circuit. The second embodiment is different from the first embodiment in that 260 is provided. Note that the configurations of the power supply circuit 111, the output voltage detection circuit 250, and the power receiving side control circuit 260 are the same as those of the wireless power transmission system S2 according to the second embodiment, and thus description thereof is omitted. Hereinafter, a description will be given focusing on differences from the first and second embodiments.

  The control circuit 141 has a function of controlling the drive frequency of the alternating current supplied from the drive circuit 120 to the power transmission side resonance circuit 130. That is, the control circuit 141 is configured to perform a frequency search operation for the drive frequency. A specific frequency search operation will be described later. The control circuit 141 also has a function of switching the output of the high voltage high power power supply 150 and the low voltage low power power supply 160 of the power supply circuit 111. In the present embodiment, the control circuit 141 controls to stop the supply of the DC voltage from the high-voltage high-power power source 150 to the drive circuit 120 during the frequency search operation of the drive frequency. That is, during the frequency search operation of the drive frequency, the control circuit 141 outputs a signal to the control terminal CNT1 so that the output of the high voltage high power power supply 150 is in a high impedance state, and the output of the low voltage low power power supply 160 is A signal is output to the control terminal CNT2 so as to be turned on. Thus, by performing the frequency search operation by the low voltage low power power supply 160 with the output of the high voltage high power power supply 150 stopped, unnecessary radiation leaking from the power transmission device 100 during the frequency search operation can be suppressed to a low level. . Further, the control circuit 141 transmits an instruction to turn on or off a switch element SW of a load 222 described later to a power receiving side control circuit 260 described later via a communication unit (not shown).

  The load 222 includes a rectifier circuit 210, a variable load Vload, and a pseudo load 241. The rectifier circuit 210 has a function of rectifying the AC power received by the power receiving coil L2 as in the first embodiment. The variable load Vload is connected between the output terminals of the rectifier circuit 210 as in the first embodiment, and stores or consumes the power converted from AC power to DC power by the rectifier circuit 210. The pseudo load 241 has a function of changing the equivalent resistance value of the load 222 to 10Ω or less. Specifically, the pseudo load 241 includes a switch element SW and a resistance element Rd1, and is connected in parallel to the variable load Vload. The switch element SW plays a role of switching connection / disconnection of the resistance element Rd1 to the variable load Vload. The resistance element Rd1 is connected in series to the switch element SW. In the present embodiment, the resistance element Rd1 is set to 10Ω or less. The pseudo load 241 configured in this manner changes the equivalent resistance value of the load 222 to 10Ω or less by switching the switch element SW to an on state by a power receiving side control circuit 260 described later.

  Here, the reason why the resistance element Rd1 of the pseudo load 241 is 10Ω or less will be described in detail with reference to FIGS.

  FIG. 8 is a graph showing frequency characteristics of the voltage across the load with respect to the equivalent resistance value of the load. In the graph shown in FIG. 8, the drive frequency (kHz) is displayed on the X axis, and the both-ends voltage Vo (V) of the load is displayed on the Y axis. In the example shown in FIG. 8, the coupling coefficient k between the power transmitting and receiving coils is set to a fixed value of 0.3, and both ends of the load when the equivalent resistance value of the load is changed to 5Ω, 10Ω, 20Ω, 100Ω, and 1 kΩ. The voltage Vo is shown.

  As shown in FIG. 8, when the equivalent resistance value of the load is 10Ω or less, there is a maximum point of the voltage Vo at both ends of the load on both the low frequency side and the high frequency side, particularly near the frequency of the maximum point on the high frequency side. It can be read that there is a frequency region P in which the change in the voltage Vo across the load is small even when the equivalent resistance value of the load changes from 5Ω to 1 kΩ. On the other hand, when the equivalent resistance value of the load is 20Ω or more, the maximum point of the voltage Vo across the load in the frequency region P disappears.

  FIG. 9 is a graph showing the frequency characteristics of the imaginary part of the impedance of the wireless power transmission network including the power transmission side resonance circuit, the power reception side resonance circuit, and the load with respect to the equivalent resistance value of the load. The graph shown in FIG. 9 displays the drive frequency (kHz) on the X axis and the imaginary part X (Ω) of the impedance Z on the Y axis. In the example shown in FIG. 9, the coupling coefficient k between the power transmitting and receiving coils is set to a fixed value of 0.3, and the impedance Z when the equivalent resistance value of the load is changed to 5Ω, 10Ω, 20Ω, 100Ω, and 1 kΩ. An imaginary part X is shown.

  As shown in FIG. 9, the imaginary part X of the impedance Z of the wireless power transmission network composed of the power transmission side resonance circuit, the power reception side resonance circuit, and the load in the vicinity of the frequency region P where the maximum point of the voltage across the load exists exists. It can be read that the expressions (5) and (6) are satisfied. As a result, when the equivalent resistance value of the load resistance is 10Ω or less, the voltage Vo across the load has a local maximum in the vicinity of the frequency region P. At this local maximum, the amount of change due to load fluctuation of the voltage Vo across the load is Minimal. Further, as an incidental characteristic, at this maximum point, the imaginary part X of the impedance Z of the wireless power transmission network composed of the power transmission side resonance circuit, the power reception side resonance circuit, and the load is expressed by the following equations (5) and (6). Satisfies. Therefore, the resistance element Rd1 of the pseudo load 241 is set to 10Ω or less, the equivalent resistance value of the load 222 is varied to 10Ω or less, and the frequency at which the voltage across the load 222 exhibits a maximum is found by the frequency search operation. By setting the drive frequency, it is possible to obtain a wireless power transmission system in which a change in the voltage across the load 222 is small with respect to a load change.

  Next, the reason why the equivalent resistance value of the load is preferably 10Ω or less even when the coupling coefficient k between the power transmitting and receiving coils is changed will be described with reference to FIG. FIG. 10 is a graph showing the maximum value of the equivalent resistance value of a load in which the voltage across the load has a local maximum in the vicinity of the frequency region P with respect to the change in the coupling coefficient between the power transmitting and receiving coils. In the graph shown in FIG. 10, the coupling coefficient k is displayed on the X axis, and the maximum value of the equivalent resistance value of the load having the maximum point near the frequency region P is displayed on the Y axis. Here, in this example, the capacitors C11 and C12 of the power transmission side resonance circuit 130 and the capacitors C21 and C22 of the power reception side resonance circuit 230 are adjusted so that the voltage across the load has a maximum point near the frequency region P. In the example shown in FIG. 10, the inductance value L10 of the power transmission coil L1 and the inductance value L20 of the power reception coil L2 are L10 = L20 = 55 μH, L10 = L20 = 74.7 μH, L10 = L20 = 95.8 μH, L10 = L20. = 141.4 μH, L10 = 128.3 μH, and L20 = 93.4 μH, the voltage across the load shows the maximum value of the equivalent resistance value of the load having a local maximum near the frequency range P . Note that the minimum coupling coefficient k between the power transmission and reception coils was set to a distance of 20 cm between the power transmission coil and the power reception coil in the facing direction.

  As shown in FIG. 10, when the coupling coefficient k between the power transmitting and receiving coils decreases, the maximum value of the equivalent resistance value of the load having a local maximum point near the frequency region P is also reduced. When the coupling coefficient k between the power transmitting and receiving coils is the minimum, as shown by the region Q in FIG. Specifically, the region Q indicates the maximum value of the equivalent resistance value of the load having a maximum point near the frequency region P where the voltage at both ends of the load is the minimum when the coupling coefficient k of each combination of the power transmitting and receiving coils is minimum. The value is about 10Ω. Therefore, when the equivalent resistance value of the load is set to 10Ω or less, the voltage at both ends of the load has a maximum point near the frequency region P even when the coupling coefficient k between the power transmission and reception coils is minimum. A frequency indicating a point is found by a frequency search operation, and by setting the frequency as a driving frequency, a wireless power transmission system in which a change in voltage across the load is small with respect to a load change can be obtained.

  Next, the frequency search operation of the wireless power transmission system S3 according to the third embodiment of the present invention will be described in detail with reference to the flowchart of FIG. FIG. 7 is a flowchart showing a frequency search operation of the wireless power transmission system according to the third embodiment of the present invention.

  Here, the frequency search operation performed by the control circuit 141 is to change the drive frequency of the drive circuit 120 within a predetermined frequency range, and to change the voltage detection signal output from the output voltage detection circuit 250 when the switch element SW is on. The frequency characteristic data corresponding to the drive frequency of the drive circuit 120 is stored in the memory, and the frequency corresponding to the maximum value of the voltage detection signal output from the output voltage detection circuit 250 when the switch element SW is in the on state is selected. . Hereinafter, the frequency search operation will be described in detail.

  First, the control circuit 141 clears all the memories related to the search, and sets the drive frequency of the drive circuit 120 to the upper limit frequency in the frequency range (predetermined frequency range) to be searched (set the initial frequency). (Step S200)

  Subsequently, the control circuit 141 turns off the high-voltage high-power power supply 150 and turns on the low-voltage low-power power supply 160 among the two types of power supplies constituting the power supply circuit 111. That is, the control circuit 140 outputs a signal to the control terminal CNT1 so that the output of the high-voltage high-power power supply 150 is in a high impedance state, and outputs a signal to the control terminal CNT2 so that the output of the low-voltage low-power power supply 160 is turned on. Is output. Thereby, a low initial voltage (about 50 V to 150 V) is supplied from the power supply circuit 111 to the drive circuit 120. (Step S201)

  Subsequently, the control circuit 141 transmits an instruction to turn on the switch element SW of the pseudo load 241 to the power receiving side control circuit 260 via the communication unit. The power receiving side control circuit 260 turns on the switch element SW of the pseudo load 241 based on an instruction from the control circuit 141. As a result, the resistance element Rd1 is connected in parallel to the variable load Vload, and the equivalent resistance value of the load 222 temporarily becomes 10Ω or less. In this state, the drive circuit 120 is operated to supply an alternating current to the power transmission side resonance circuit 130. (Step S202)

  When AC current is supplied from the drive circuit 120 to the power transmission side resonance circuit 130, the power transmission coil L1 generates an AC magnetic field based on the AC current, and the power receiving coil L2 receives AC power via the AC magnetic field. Then, the rectifier circuit 210 converts AC power received by the power receiving coil L2 into DC power and supplies it to the variable load Vload. At this time, the output voltage detection circuit 250 detects the output voltage value of the rectifier circuit 210 and outputs it to the power receiving side control circuit 260 as a voltage detection signal. The power receiving side control circuit 260 transmits the voltage value detected by the output voltage detection circuit 250 to the control circuit 141 via the communication means. (Step S203)

  Subsequently, the control circuit 141 stores the set of the voltage value and the initial frequency transmitted from the power receiving side control circuit 260 in step S203 in the search memory in the control circuit 141 as array data. (Step S204)

  Subsequently, the control circuit 141 drives the drive circuit 120 by changing the drive frequency of the drive circuit 120 from the initial frequency to a lower frequency in the frequency range in which the drive circuit 120 is searched. (Step S205) The output voltage value of the rectifier circuit 210 at this time is detected by the output voltage detection circuit 250, and is output to the power receiving side control circuit 260 as a voltage detection signal. The power receiving side control circuit 260 transmits the voltage value detected by the output voltage detection circuit 250 to the control circuit 141 via the communication means. (Step S206) Then, the control circuit 141 additionally stores the set of the voltage value and the changed frequency transmitted from the power receiving side control circuit 260 in step S206 as array data in the search memory in the control circuit 141 in the order of array numbers. To do. (Step S207)

  Subsequently, the output voltage value of the rectifier circuit 210 with the array element number second from the tail stored in the search memory of the control circuit 141 is compared with the output voltage value of the rectifier circuit 210 acquired in step S207 (step S208). ), The processing operation is stopped when the output voltage value of the rectifier circuit 210 acquired in step S207 is equal to or lower than the output voltage value of the rectifier circuit 210 having the second array element number stored in the search memory. Are stored in the setting memory in the control circuit 141 (step S208Y). When the output voltage value of the rectifier circuit 210 acquired in step S207 is larger than the output voltage value of the rectifier circuit 210 having the second array element number from the last stored in the search memory (step S208N), the frequency to be changed The lower limit frequency in the frequency range to be searched is compared (step S209), and when the frequency to be changed reaches the lower limit frequency in the frequency range to be searched, the processing operation is stopped and the frequency of the last array element number is controlled by the control circuit. 141 is stored in the setting memory in step 141 (step S209Y). On the other hand, when the frequency to be changed does not reach the lower limit frequency in the frequency range to be searched (step S209N), the processing operations from step S205 to step S209 are repeatedly executed.

  Then, the control circuit 141 sets the frequency stored in the setting memory to the drive frequency of the drive circuit 120 (step S210). In this way, when the drive frequency of the drive circuit 120 is set to the frequency stored in the setting memory, the control circuit 141 turns off the switch element SW of the pseudo load 241 to the power receiving side control circuit 260 via the communication unit. Send an instruction to set the status. The power receiving side control circuit 260 turns off the switch element SW of the pseudo load 241 based on an instruction from the control circuit 141. As a result, the resistance element Rd1 is disconnected from the variable load Vload, the equivalent resistance value of the load 222 returns to the original high state, and the frequency search operation ends (step S211). As described above, the frequency search operation performed by the control circuit 141 is to set the drive frequency to a frequency corresponding to the maximum value of the voltage value detected by the output voltage detection circuit 250 when the switch element SW is in the ON state. is there.

  When the frequency search operation is completed and the control circuit 141 sets the frequency stored in the setting memory to the drive frequency of the drive circuit 120, the control circuit 141 is the high power source among the two types of power supplies constituting the power supply circuit 111. The high voltage power source 150 is turned on, and the low voltage low power source 160 is turned off. That is, the control circuit 140 outputs a signal to the control terminal CNT1 so that the output of the high voltage high power source 150 is turned on, and outputs a signal to the control terminal CNT2 so that the output of the low voltage low power source 160 is in a high impedance state. Is output. As a result, in the wireless power transmission system S3, the voltage across the load 222 (the output voltage of the rectifier circuit 210) is boosted to a desired voltage value, and the voltage across the load 222 is unlikely to change due to load fluctuations. It becomes possible to transmit electric power.

  As described above, in the wireless power transmission system S3 according to the present embodiment, the power transmission device 100 further includes the control circuit 141 that controls the drive frequency, and the power receiving device 200 detects the voltage across the load 222. The load 222 further includes a circuit 250. The load 222 rectifies the AC power received by the power receiving coil L2, a variable load Vload connected between the output terminals of the rectifier circuit 210, and the variable load Vload in parallel. A switching element SW connected and a pseudo load 241 composed of a resistance element Rd1 connected in series to the switching element SW, the resistance element Rd1 is 10Ω or less, and the control circuit 141 includes a switching element SW Frequency search for setting the drive frequency to a frequency at which the voltage value detected by the output voltage detection circuit 250 becomes a maximum value in the ON state It is doing the work. Therefore, when the switch element SW of the pseudo load 241 is turned on, the output is output even when the load 222 is small (when the equivalent resistance value of the load 222 is large) or when the separation distance between the power transmitting and receiving coils is large and the magnetic coupling is weak. The voltage detection circuit 250 can detect the maximum value of the voltage across the load 222, and the frequency corresponding to the maximum value is substantially the same as the frequency at which the change in the voltage across the load 222 is minimized with respect to the load fluctuation. It becomes. Therefore, when the frequency corresponding to the maximum value is set to the frequency of the drive circuit 120 and the power is transmitted after the switch element SW is returned to the off state (shut off state), the voltage across the load 222 against the load fluctuation Variations can be suppressed.

  In the wireless power transmission system S3 according to the present embodiment, the power transmission apparatus 100 further includes a high voltage high power power source 150 and a low voltage low power power source 160, and the drive circuit 120 includes the high voltage high power power source 150 or a low power source. The DC voltage supplied from the low voltage power source 160 is converted into an AC voltage, and the high voltage high power source 150 stops supplying the DC voltage to the drive circuit 120 during the frequency search operation. Therefore, unnecessary radiation leaking from the power transmission device 100 during the frequency search operation can be suppressed to a low level by performing the frequency search operation by the low-voltage low-power power supply 160 in a state where the output of the high-voltage high-power power supply 150 is stopped.

(Fourth embodiment)
Next, the configuration of the wireless power transmission system S4 according to the fourth embodiment of the present invention will be described with reference to FIG. FIG. 11 is a configuration diagram illustrating a wireless power transmission system according to the fourth embodiment of the present invention.

  The wireless power transmission system S4 includes a power transmission device 100 and a power reception device 200, as in the second embodiment. In the wireless power transmission system S <b> 4, power is transmitted wirelessly from the power transmission device 100 to the power reception device 200. In the present embodiment, the power transmission device 100 includes a power supply circuit 111, a drive circuit 120, a power transmission side resonance circuit 130, a control circuit 142, and a position adjustment unit 170. The power receiving device 200 includes a power receiving side resonance circuit 230, a load 221, an output voltage detection circuit 250, and a power receiving side control circuit 260. The configuration of the power supply circuit 111, the drive circuit 120, the power transmission side resonance circuit 130, the power reception side resonance circuit 230, the load 221, the output voltage detection circuit 250, and the power reception side control circuit 260 is the same as that of the wireless power transmission system S2 according to the second embodiment. It is the same. That is, the wireless power transmission system S4 according to the fourth embodiment is different from the second embodiment in that a control circuit 142 is provided instead of the control circuit 140 and a position adjusting unit 170 is provided. The wireless power transmission system S4 according to the fourth embodiment may include a control circuit 142 instead of the control circuit 141 in the wireless power transmission system S3 according to the third embodiment, and may include a position adjusting unit 170. . Hereinafter, a description will be given focusing on differences from the second embodiment.

  Similar to the control circuit 140 according to the second embodiment, the control circuit 142 has a function of controlling the drive frequency of the alternating current supplied from the drive circuit 120 to the power transmission side resonance circuit 130. That is, the control circuit 142 is configured to perform a frequency search operation for the drive frequency. The control circuit 142 also has a function of switching the outputs of the high voltage high power power supply 150 and the low voltage low power power supply 160. In the present embodiment, the control circuit 142 outputs a control signal to move the position of the power transmission coil L1 or the power reception coil L2 to the position adjustment unit 170 described later so that the drive frequency obtained by the frequency search operation becomes the highest. . Here, “the drive frequency is the highest” means that an error range of about ± 0.5 kHz of the maximum value is included in addition to the maximum value of the drive frequency. A specific position adjustment operation will be described later.

  The position adjusting unit 170 has a function of moving the position of the power transmission coil L1 or the power reception coil L2. In the present embodiment, the position adjusting unit 170 has a function of moving the physical position of the power transmission coil L1, but is not particularly limited as long as the power transmission coil L1 moves, and the power transmission side provided with the power transmission coil L1. The physical position of the resonance circuit 130 may be moved, or the physical position of the entire power transmission device 100 may be moved. Similarly, when the position adjusting unit 170 has a function of moving the position of the power receiving coil L2, there is no particular limitation as long as the power receiving coil L2 moves, and the physical position of the power receiving coil L2 may be moved. The physical position of the power receiving resonance circuit 230 including the power receiving coil L2 may be moved, or the physical position of the entire power receiving apparatus 200 may be moved. The position adjusting unit 170 is configured by an actuator or the like that is driven based on a control signal from the control circuit 142, and the power transmission coil L1 or the power reception coil L2 is in an in-plane direction (perpendicular to the facing direction of the power transmission coil L1 and the power reception coil L2) Direction). Note that the position adjustment unit 170 may be disposed in the power transmission device 100 or the power reception device 200, or may be disposed outside the power transmission device 100 or the power reception device 200.

  Here, the position adjustment operation according to the present embodiment will be described in detail. In this description, the case where the wireless power transmission system S4 according to the present embodiment is applied to a power supply facility for a vehicle such as an electric vehicle will be described. First, when the vehicle is parked in the power feeding area, the control circuit 142 performs a frequency search operation to obtain a driving frequency. This drive frequency is set as a reference frequency. Next, the control circuit 142 outputs a control signal to the position adjusting unit 170 so as to move the position of the power transmission coil L1 in the vehicle width direction. The position adjusting unit 170 moves the position of the power transmission coil L <b> 1 based on the control signal of the control circuit 142. Next, the control circuit 142 performs a frequency search operation again, compares the obtained drive frequency with the reference frequency, and if the obtained drive frequency is high, the direction in which the position of the power transmission coil L1 in the vehicle width direction is moved. Move further. On the other hand, if the reference frequency is high, the power transmission coil L1 is moved in the direction opposite to the direction in which the position in the vehicle width direction is moved. The control circuit 142 repeats this operation, and ends the position adjustment operation in the vehicle width direction when the position of the power transmission coil L1 in the vehicle width direction where the drive frequency is highest is specified. Next, the control circuit 142 specifies the position of the power transmission coil L1 in the vehicle length direction where the drive frequency is highest, using the same method as the position adjustment operation in the vehicle width direction. The position adjustment operation in the length direction is terminated. Thereby, the position of the power transmission coil L1 with the highest drive frequency is specified. In other words, the position of the power transmission coil L1 is moved by the position adjusting means 170 so that the drive frequency becomes the highest. In this description, the position adjustment is performed in two stages of the vehicle width direction and the vehicle length direction. However, the position adjustment is not limited to this, and the position adjustment is performed by freely moving the power transmission coil L1 in the in-plane direction. You may go.

  As described above, when the power transmission coil L1 is moved to the position where the drive frequency becomes the highest by the position adjusting unit 170, the relative separation distance between the power transmission coil L1 and the power reception coil L2 becomes the smallest. Therefore, the magnetic flux generated by the power transmission coil L1 is efficiently linked to the power reception coil L2, and the magnetic flux leaking from the power transmission coil L1 is also reduced. As a result, it is possible to reduce unnecessary radiation while maintaining high power transmission efficiency.

  As described above, the wireless power transmission system S4 according to the present embodiment further includes the position adjustment unit 170 that moves the position of the power transmission coil L1 or the power reception coil L2, and the position adjustment unit 170 has the highest drive frequency. The position of the power transmission coil L1 or the power reception coil L2 is moved. Therefore, since the relative positional deviation between the power transmission coil L1 and the power reception coil L2 can be reduced, the change in the voltage at both ends of the load with respect to load fluctuations while maintaining high power transmission efficiency and low unnecessary radiation. It is possible to realize a stable power supply with reduced noise.

  According to the wireless power transmission system of the present invention, it is possible to realize a wireless power transmission system in which the fluctuation of the voltage across the load with respect to the fluctuation of the equivalent resistance of the load is suppressed.

  DESCRIPTION OF SYMBOLS 100 ... Power transmission apparatus, 110, 111 ... Power supply circuit, 120 ... Drive circuit, 130 ... Power transmission side resonance circuit, 140, 141, 142 ... Control circuit, 150 ... High voltage high power power source, 160 ... Low voltage low power power source, 170 ... Position adjusting means, 180 ... Commercial power supply, L1 ... Power transmission coil, C1 ... Power transmission side capacitor part, C11, C12 ... Capacitor of power transmission side capacitor part, T1, T3 ... High voltage output terminal, T2, T4 ... GND terminal, T5 ... High voltage input terminal, T6: Low voltage input terminal, CNT1, CNT2 ... Control terminal, D1 ... Diode, 200 ... Power receiving device, 210 ... Rectifier circuit, 220, 221, 222 ... Load, 230 ... Power receiving side resonance circuit, 240, 241 ... Pseudo load, 250 ... output voltage detection circuit, 260 ... power reception side control circuit, L2 ... power reception coil, C2 ... power reception side capacitor section, C21, C22 Receiving-side capacitor of the capacitor, Vload ... variable load, SW ... switching device, Rd, Rd1 ... resistance element, S1 to S4 ... wireless power transmission system.

Claims (6)

A wireless power transmission system for transmitting AC power wirelessly from a power transmitting device to a power receiving device,
The power transmission device includes a power transmission side resonance circuit having a power transmission coil and a power transmission side capacitor unit, and a drive circuit that supplies an alternating current to the power transmission side resonance circuit at a drive frequency,
The power receiving device includes a power receiving side resonance circuit having a power receiving coil and a power receiving side capacitor, and a load to which power is supplied from the power receiving side resonance circuit,
When the power transmission side resonance circuit is viewed from the drive circuit, an F matrix of a four-terminal network composed of the power transmission side resonance circuit and the power reception side resonance circuit is expressed by Equation (1), and F of the four-terminal circuit network If the real part of A in the matrix is Ra, the imaginary part is Xa, the real part of B in the F matrix of the four-terminal network is Rb, the imaginary part is Xb, and the equivalent resistance of the load is RL0,
A wireless power transmission system, wherein A and B of the F matrix satisfy the following expressions (2), (3), and (4):

(However, j ² = −1.)

The drive frequency is f, the change in the drive frequency is δf, the imaginary part of the impedance of the wireless power transmission network composed of the power transmission side resonance circuit, the power reception side resonance circuit and the load is X, and the imaginary part is If the change with respect to the drive frequency is δX,
The wireless power transmission system according to claim 1, wherein the drive frequency f satisfies the following expressions (5) and (6).

The power transmission device further includes a control circuit that controls the drive frequency,
The power receiving device further includes an output voltage detection circuit that detects a voltage across the load,
The load includes a rectifier circuit that rectifies AC power received by the power receiving coil, a variable load connected between output terminals of the rectifier circuit, a switch element connected in parallel to the variable load, and the switch Including a pseudo load composed of a resistance element connected in series to the element,
The control circuit has a minimum difference between a voltage value detected by the output voltage detection circuit when the switch element is on and a voltage value detected by the output voltage detection circuit when the switch element is off. The wireless power transmission system according to claim 1, wherein a frequency search operation for setting the drive frequency to a frequency is performed. The power transmission device further includes a control circuit that controls the drive frequency,
The power receiving device further includes an output voltage detection circuit that detects a voltage across the load,
The load includes a rectifier circuit that rectifies AC power received by the power receiving coil, a variable load connected between output terminals of the rectifier circuit, a switch element connected in parallel to the variable load, and the switch Including a pseudo load composed of a resistance element connected in series to the element,
The resistance element is 10Ω or less,
The control circuit performs a frequency search operation for setting the drive frequency to a frequency at which the voltage value detected by the output voltage detection circuit becomes a maximum value when the switch element is on. Wireless power transmission system as described in. The power transmission device further includes a high voltage high power power source and a low voltage low power power source,
The drive circuit converts a DC voltage supplied from the high voltage high power power source or the low voltage low power power source into an AC voltage,
5. The wireless power transmission system according to claim 3, wherein the high-voltage high-power power supply stops the supply of a DC voltage to the drive circuit during the frequency search operation. A position adjusting means for moving the position of the power transmission coil or the power reception coil;
The wireless power transmission system according to any one of claims 3 to 5, wherein the position adjusting unit moves the position of the power transmission coil or the power reception coil so that the drive frequency becomes the highest.

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