WO2013153841A1

WO2013153841A1 - Non-contact power transmission system

Info

Publication number: WO2013153841A1
Application number: PCT/JP2013/052634
Authority: WO
Inventors: 博紀酒井
Original assignee: 株式会社村田製作所
Priority date: 2012-04-13
Filing date: 2013-02-05
Publication date: 2013-10-17
Also published as: CN204145084U; JP5794444B2; JPWO2013153841A1

Abstract

A power transmission device (10) comprises a power transmission side active electrode (E1) and a power transmission side passive electrode (E2) disposed along the upper surface of a housing (CB1). A power receiving device (30) comprises a power receiving side active electrode (E3) and a power receiving side passive electrode (E4) disposed along the upper surface of a housing (CB2). Herein, the size of each of the power transmission side active electrode (E1) and the power receiving side active electrode (E3) is adjusted so that the power receiving side active electrode (E3) is accommodated in the outer edge of the power transmission side active electrode (E1) when viewed from the direction orthogonal to each of the upper surfaces in a specific state where the upper surface of the housing (CB1) faces the upper surface of the housing (CB2). Also, the power transmission side active electrode (E1) is divided by notches (CT1 to CT5), and the arrangement of the notches (CT1 to CT5) is adjusted so that part of the power receiving side passive electrode (E4) faces part of the notches (CT1 to CT5) in the specific state.

Description

Non-contact power transmission system

The present invention relates to a contactless power transmission system, and more particularly to a contactless power transmission system that transmits electric power from a power transmission device to a power reception device using an electric field.

An example of this type of system is disclosed in Patent Document 1. According to this background art, the power feeding device has two power feeding electrodes respectively connected to one end and the other end of the resonance unit. The AC signal generated in the resonance part is applied to the two power supply electrodes and radiated to the outside as a potential difference in the electrostatic field. On the other hand, the power receiving device includes 16 power receiving electrodes that sense a potential difference radiated from the power feeding device, and a selection determination unit that classifies these power receiving electrodes into a first set and a second set. The electric signal output from the power receiving electrode belonging to the first set is applied to one end of the resonance part, the electric signal output from the power receiving electrode belonging to the second set is applied to the other end of the resonance part, and the resonance The output of the unit is supplied to the load through the rectifying unit.

JP 2009-296857 A

However, in the background art, since the feeding electrode is much larger than the receiving electrode, the capacity of the receiving electrode on the side belonging to the second set having the opposite polarity to that of the first feeding electrode is increased. May decrease.

Therefore, a main object of the present invention is to provide a non-contact power transmission system that can avoid a decrease in power transmission efficiency.

A non-contact power transmission system according to the present invention includes a first power transmission electrode (AC1) that is provided along a first main surface of a first housing (CB1: reference numeral corresponding to the embodiment; the same applies hereinafter) to which an AC voltage is applied. E1) and a power transmission device (10) including a second power transmission electrode (E2), and an electric field coupling with the first power transmission electrode and the second power transmission electrode provided along the second main surface of the second housing (CB2). A non-contact power transmission system formed by a power receiving device (20) including a first power receiving electrode (E3) and a second power receiving electrode (E4), each size of the first power transmitting electrode and the first power receiving electrode Is adjusted so that the first power receiving electrode is within the outer edge of the first power transmitting electrode when viewed from the direction orthogonal to the second main surface in a specific state where the second main surface is opposed to the first main surface. The electrode is divided into a plurality of partial electrodes (E1_1 to E1_6) by the notch, and the arrangement of the notch is in a specific state. Part of the second power receiving electrode is adjusted so as to face the notch Te.

Preferably, the notch is formed so that a plurality of partial electrodes (E1_1 to E1_6) are arranged in the first direction.

More preferably, each of the plurality of partial electrodes forms a strip extending in the second direction orthogonal to the first direction, and the maximum distance between two points assigned to the outline of the first power receiving electrode is the width of the notch and the length of the strip. It exceeds the distance corresponding to the sum of the width.

Preferably, the main surface of the second power receiving electrode has a rectangular shape, the second power transmitting electrode has a rectangular opening for accommodating the first power transmitting electrode, and the length of the short side of the rectangle forming the main surface of the second power receiving electrode is It is larger than the length of the short side of the rectangle forming the opening.

Preferably, the main surface of the second power receiving electrode has a size covering the main surface of the first power receiving electrode, and the first power receiving electrode is stacked on the second power receiving electrode toward the outside of the second housing.

Preferably, the second main surface has a size covered by the first main surface, and the specific state is a positional relationship in which the second main surface is within the outer edge of the first main surface when viewed from a direction orthogonal to the second main surface. Assuming

Preferably, there is further provided selection means (SW2) for selecting any one of the plurality of partial electrodes as an AC voltage application destination, and control means (16) for controlling the operation of the selection means with reference to impedance characteristics. .

According to this invention, when the power receiving device is brought close to the power transmitting device in a posture in which the second main surface faces the first main surface, the AC voltage is changed to the first power transmitting electrode, the second power transmitting electrode, the first power receiving electrode, and the second power receiving The power is transmitted from the power transmission device to the power reception device via the electrode.

Here, each of the first power transmission electrode and the first power reception electrode has the first power reception electrode viewed from the direction orthogonal to the second main surface in a specific state in which the second main surface is opposed to the first main surface. The size fits within the outer edge of the power transmission electrode. Accordingly, when the relative position of the power receiving device is changed along the first main surface, the amount of change in the coupling capacitance between the first power transmission electrode and the first power receiving electrode is suppressed compared to the amount of change in the relative position. .

Also, the first power transmission electrode is divided into a plurality of partial electrodes by the notch, and the arrangement of the notch is adjusted so that a part of the second power receiving electrode faces the notch in a specific state. Thereby, the capacity | capacitance of a 2nd receiving electrode and a 1st power transmission electrode is suppressed. Thus, a decrease in power transmission efficiency is avoided.

The above object, other objects, features, and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

It is a perspective view which shows an example of the external appearance of the power transmission apparatus applied to the non-contact electric power transmission system of this Example. It is a perspective view which shows an example of the external appearance of the power receiving apparatus applied to the non-contact electric power transmission system of this Example. (A) is an illustration figure which shows an example of an electrode raw material, (B) is an illustration figure which shows an example of the power transmission side active electrode produced by forming a notch in an electrode raw material. (A) is an illustration figure which shows another example of an electrode raw material, (B) is an illustration figure which shows an example of the power transmission side passive electrode produced by forming opening in an electrode raw material. It is an illustration figure which shows an example of a receiving side active electrode and a receiving side passive electrode. It is an illustration figure which shows an example of the difference in size between a power transmission apparatus and a power receiving apparatus. (A) is an illustration figure which shows an example of the positional relationship of a power transmission apparatus and a power receiving apparatus, (B) is an illustration figure which shows another example of the positional relationship of a power transmission apparatus and a power receiving apparatus. (A) is an illustration figure which shows the other example of the positional relationship of a power transmission apparatus and a power receiving apparatus, (B) is an illustration figure which shows another example of the positional relationship of a power transmission apparatus and a power receiving apparatus. (A) is an illustrative view showing another example of the positional relationship between the power transmitting device and the power receiving device, and (B) is an illustrative view showing another example of the positional relationship between the power transmitting device and the power receiving device. It is a block diagram which shows an example of a structure of the non-contact electric power transmission system of this Example. It is an illustration figure which shows an example of a structure of the switch circuit applied to a power transmission apparatus. It is a flowchart which shows a part of operation | movement of CPU applied to a power transmission apparatus. It is a flowchart which shows a part of other operation | movement of CPU applied to a power transmission apparatus. (A) is an illustrative view showing another example of the power transmission side active electrode, and (B) is an illustrative view showing another example of the power transmission side active electrode. It is an illustration figure which shows an example of the power transmission apparatus and power receiving apparatus which are applied to another Example. It is a block diagram which shows a part of structure of the power transmission apparatus applied to another Example.

The contactless power transmission system of this embodiment is formed by the power transmission device 10 shown in FIG. 1 and the power reception device 30 shown in FIG. The power transmission device 10 has a plate-like casing CB1 provided with a power transmission side active electrode E1 and a power transmission side passive electrode E2, and the power reception device 30 is a plate provided with a power reception side active electrode E3 and a power reception side passive electrode E4. The housing CB2 has a shape. More specifically, the power transmission side active electrode E1 and the power transmission side passive electrode E2 are provided along the upper surface of the housing CB1, and the power reception side active electrode E3 and the power reception side passive electrode E4 are provided along the upper surface of the housing CB2. The power transmission side active electrode E1 is formed by six partial electrodes E1_1 to E1_6.

The power transmission side active electrode E1 is produced based on the electrode material EM1 shown in FIG. The electrode material EM1 has a rectangular main surface with long sides and short sides extending in the X direction and the Y direction, respectively, and is formed in a plate shape. Here, the thickness of the electrode material EM1 is much smaller than the thickness of the housing CB1.

In the electrode EM1, notches CT1 to CT5 each having a width corresponding to “W1” and extending in the Y direction are formed as shown in FIG. The notches CT1 to CT5 are formed at the same distance in the X direction. Thus, strip-shaped partial electrodes E1_1 to E1_6 having a common size are obtained. Each main surface of the partial electrodes E1_1 to E1_6 has a short side extending in the X direction and a long side extending in the Y direction. The length of the short side corresponds to “X1”, while the length of the long side is Corresponds to “Y1”.

The power transmission side passive electrode E2 is produced based on the electrode material EM2 shown in FIG. The electrode material EM2 has a rectangular main surface with long sides and short sides extending in the X direction and the Y direction, respectively, and is formed in a plate shape. Here, the thickness of the electrode material EM2 is also much smaller than the thickness of the housing CB1. The length of the long side corresponds to “X2a”, while the length of the short side corresponds to “Y2a”. Furthermore, the size of the main surface of the electrode material EM2 matches the size of the upper surface of the housing CB1.

When the rectangular opening OP1 is formed in the center of the electrode material EM2, a power transmission side passive electrode E2 shown in FIG. 4B is obtained. Here, the long side and the short side of the rectangle forming the opening OP1 extend in the X direction and the Y direction, the length of the long side corresponds to “X2b”, and the length of the short side corresponds to “Y2b”. The length of the short side of the rectangle forming the opening OP1 is larger than the length of the short side of the rectangle forming the main surface of the electrode member EM1, and the length of the long side of the rectangle forming the opening OP1 is the length of the electrode member EM1. It is larger than the length of the long side of the rectangle forming the main surface.

As shown in FIG. 1, the power transmission side active electrode E1 is provided at the center of the upper surface of the casing CB1. The power transmission side passive electrode E2 is provided on the upper surface of the housing CB1 so that the outer edge of the upper surface of the housing CB1 coincides with the outer edge of the main surface of the power transmission side passive electrode E2. Since the sizes of the power transmission side active electrode E1 and the power transmission side passive electrode E2 are as described above, the power transmission side active electrode E1 is accommodated in the opening OP1 provided in the power transmission side passive electrode E2.

Referring to FIG. 5, the power receiving side active electrode E3 is formed in a plate shape having a square main surface with each side extending in the X direction or the Y direction. Here, the length of each side corresponds to “X3” or “Y3”. The power receiving side passive electrode E4 has a rectangular main surface with a short side and a long side extending in the X direction and the Y direction, respectively, and is formed in a plate shape. Here, while the length of the short side corresponds to “X4”, the length of the long side corresponds to “Y4”, and both the short side and the long side have the length of each square forming the power receiving side active electrode E3. It is larger than the side length.

The size of the main surface of the power receiving side passive electrode E4 matches the size of the upper surface of the housing CB2, and the power receiving side passive electrode E4 has the outer edge of the upper surface of the housing CB2 aligned with the outer edge of the main surface of the power transmitting side passive electrode E2. Are provided on a plane parallel to the upper surface of the casing CB2. The power receiving-side active electrode E3 is stacked on the power receiving-side passive electrode E4 (that is, toward the outside of the housing CB2) at a certain distance corresponding to the center position of the upper surface of the housing CB2.

Since the sizes of the power transmission side active electrode E1, the power transmission side passive electrode E2, the power reception side active electrode E3, and the power reception side passive electrode E4 are set as described above, the power transmission device 10 and the power reception device 30 have the size relationship shown in FIG. Indicates.

7A to 7B, 8A to 8B, and 9A to 9 showing a state where the power receiving device 30 is placed on the power transmitting device 10. FIG. As can be seen from (B), the upper surface of the housing CB2 has a size covered by the upper surface of the housing CB1. In addition, the sizes of the power transmission side active electrode E1 and the power reception side active electrode E3 are determined based on the power receiving side active when viewed from the direction orthogonal to each upper surface in a specific state where the upper surface of the housing CB1 is opposed to the upper surface of the housing CB2. The electrode E3 is adjusted so as to be within the outer edge or contour of the power transmission side active electrode E1 (the outer edge or contour is defined by a broken line in FIG. 6). In the specific state described above, a part of the power receiving side passive electrode E4 faces a part of the notches CT1 to CT5.

Note that the specific state is premised on a positional relationship in which the top surface of the housing CB2 is within the outer edge or contour of the top surface of the housing CB1 when viewed from a direction orthogonal to the top surface of the housing CB2.

The maximum distance between the two points assigned to the contour of the power receiving side active electrode E3 is the width W1 of each of the cutouts CT1 to CT5 and the length X1 of the short side that forms the main surface of each of the partial electrodes E1_1 to E1_6. It exceeds the distance equivalent to the sum of Further, the length X4 of the rectangular short side forming the main surface of the power receiving side passive electrode E4 is larger than the length Yb2 of the rectangular short side forming the opening OP1 provided in the power transmitting side passive electrode E2.

Referring to FIG. 10, power transmission device 10 includes a DC power supply 12. The DC power supply 12 applies a DC voltage to the input terminal of the switch SW1 connected to either one of the terminals T1 and T2. The terminal T1 is directly connected to the inverter 18, and the terminal T2 is connected to the inverter 18 via the resistor R1. Therefore, when the switch SW1 is connected to the terminal T1, a DC voltage is supplied to the inverter 18, and when the switch SW1 is connected to the terminal T2, the voltage dropped by the resistor R1 is supplied to the inverter 18.

The inverter 18 is turned on during a period when the PWM signal output from the PWM generation circuit 14 is at the H level, and is turned off during a period when the PWM signal output from the PWM generation circuit 14 is at the L level. Inverter 18 is also connected to primary winding Np1 among primary winding Np1 and secondary winding Ns1 forming transformer 20.

Therefore, when the inverter 18 is turned on / off as described above, an AC voltage is excited in the secondary winding Ns1. However, the number of turns of the secondary winding Ns1 is larger than the number of turns of the primary winding Np1, and the AC voltage appearing in the secondary winding Ns1 is higher than the AC voltage appearing in the primary winding Np1. The frequency and height of the AC voltage appearing in each of the primary winding Np1 and the secondary winding Ns1 depend on the frequency and duty ratio of the PWM signal, respectively.

The one end of the secondary winding Ns1 is connected to the power transmission side active electrode E1 via the switch circuit SW2, and the other end of the secondary winding Ns1 is directly connected to the power transmission side passive electrode E2. As shown in FIG. 11, the switch circuit SW2 is formed by switches SW2_1 to SW2_6 that are assigned to the partial electrodes E1_1 to E1_6 and are selectively turned on. Therefore, the AC voltage excited in the secondary winding Ns1 is applied to any one of the partial electrodes E1_1 to E1_6 and the power transmission side passive electrode E2.

AC voltage is excited by the electric field coupling in the power receiving side active electrode E3 and the passive side power receiving electrode E4. The excited AC voltage has a frequency corresponding to the frequency of the AC voltage applied to the power transmission side active electrode E1 and the power transmission side passive electrode E2 and a height depending on the electric field coupling degree.

The alternating voltage thus excited is supplied to the load 34 via the primary winding Np2 and the secondary winding Ns2 forming the transformer 32. However, the number of turns of the secondary winding Ns2 is smaller than the number of turns of the primary winding Np2, and the AC voltage supplied to the load 34 is higher than the AC voltage excited by the power receiving side active electrode E3 and the passive side power receiving electrode E4. Indicates a low value.

The CPU 16 provided in the power transmission device 10 adjusts the setting of the switch SW2 and the frequency of the PWM signal in the following manner when starting the power supply to the power receiving device 30 that is electric field coupled.

CPU 16 first connects the connection destination of switch SW1 to terminal T2, and initializes the frequency and duty ratio of the PWM signal. The PWM generation circuit 14 supplies a PWM signal having an initial frequency and a duty ratio to the inverter 18. As a result, an AC voltage having a height and frequency depending on the duty ratio and frequency is excited in the secondary winding Ns1 of the transformer 20.

Subsequently, the CPU 16 sets the variable K to “1” to “6”, and turns on only the switch SW2_K among the switches SW2_1 to SW2_6. The frequency of the PWM signal is swept, and in parallel with this, the impedance characteristic on the transformer 20 side of the inverter 18 is measured. In the measurement, the voltage at the input terminal of the inverter 18 is referred to. With reference to the measured impedance characteristic, the connection state of the switch SW2 and the frequency of the PWM signal corresponding to the maximum value when the impedance value indicates an impedance characteristic that falls within the predetermined range are searched. The switch SW2 is set to the detected connection state, and the frequency of the PWM signal is set to the detected frequency. When the setting is completed, the switch SW1 is connected to the terminal T1. Thereby, power supply to the power receiving device 30 is started.

Specifically, the CPU 16 executes processing according to the flowcharts shown in FIGS. A control program corresponding to this flowchart is stored in the flash memory 16m.

Referring to FIG. 12, in step S1, switch SW1 is connected to terminal T2, and in step S3, the frequency and duty ratio of the PWM signal are initialized. The PWM generation circuit 14 supplies a PWM signal having a set frequency and duty ratio to the inverter 18.

In step S5, the variable K is set to “1”, and in step S7, only the switch SW2_K among the switches SW2_1 to SW2_6 is turned on. In step S9, the frequency of the PWM signal is swept, and in parallel with this, the impedance characteristic on the transformer 20 side of the inverter 18 is measured. In the measurement, the voltage at the input terminal of the inverter 18 is referred to. In step S11, the impedance maximum value is searched with reference to the measured impedance characteristic.

In step S13, it is determined whether or not the maximum value has been detected. If the determination result is NO, the process proceeds to step S17, and if the determination result is YES, the process proceeds to step S15. In step S15, it is determined whether or not the detected maximum value belongs to the predetermined range. If the determination result is NO, the process proceeds to step S17, and if the determination result is YES, the process proceeds to step S25.

In step S17, the variable K is incremented, and in step S19, it is determined whether or not the current value of the variable K exceeds “6”. If a determination result is NO, it will return to step S7 as it is. On the other hand, if the determination result is YES, it waits for a predetermined time in step S21, sets the variable K to “1” in step S23, and then returns to step S7.

In step S25, the frequency at which the impedance has a maximum value is set as the frequency of the PWM signal. When the setting is completed, the switch SW1 is connected to the terminal T1 in step S27, and then the process ends.

As can be seen from the above description, the power transmission device 10 includes a power transmission side active electrode E1 and a power transmission side passive electrode E2 that are provided along the upper surface of the housing CB1 and to which an AC voltage is applied. The power receiving device 30 includes a power receiving side active electrode E3 and a power receiving side passive electrode E4 that are provided along the upper surface of the housing CB2 and are electrically coupled to the power transmitting side active electrode E1 and the power transmitting side passive electrode E2.

Here, the size of each of the power transmitting side active electrode E1 and the power receiving side active electrode E3 is such that the upper surface of the housing CB1 faces the upper surface of the housing CB2 and is viewed from the direction orthogonal to each upper surface. The side active electrode E3 is adjusted so as to be within the outer edge of the power transmission side active electrode E1. Further, the power transmission side active electrode E1 is divided into partial electrodes E1_1 to E1_6 by notches CT1 to CT5. It is adjusted so as to face a part of.

By adjusting the sizes of the power transmission side active electrode E1 and the power reception side active electrode E3 as described above, when the relative position of the power reception device 30 is changed in the direction along each upper surface, the power transmission side active electrode E1 and the power reception side active The fluctuation amount of the coupling capacitance with the electrode E3 is suppressed as compared with the fluctuation amount of the relative position.

Further, the power transmission side active electrode E1 is divided into partial electrodes E1_1 to E1_6 by notches CT1 to CT5, and in a specific state, the power receiving side passive electrode E4 is partly cut away so as to face a part of the notches CT1 to CT5. By adjusting the arrangement of the notches CT1 to CT5, the coupling capacitance between the power receiving side passive electrode E4 and the power transmitting side active electrode E1 is suppressed. Thus, a decrease in power transmission efficiency is avoided.

In this embodiment, each of the partial electrodes E1_1 to E1_6 is formed in a rectangular shape. However, the shape of each of the partial electrodes E1_1 to E1_6 is not limited to a rectangular shape, and FIG. You may make it employ | adopt the parallelogram shown or the gourd shape shown to FIG. 14 (B). In addition, although the power receiving side active electrode E3 is formed in a square shape, it may have a rectangular shape in which the lengths of the sides X3 and Y3 are different as long as the above relationship is satisfied.

Further, in this embodiment, one end of the secondary winding Ns1 is connected to one of the partial electrodes E1_1 to E1_6, and the other end of the secondary winding Ns1 is connected to the power transmission side passive electrode E2. However, one end of the secondary winding Ns1 may be connected to one of the partial electrodes E1_1 to E1_6, and the other end of the secondary winding Ns1 may be connected to the other one of the partial electrodes E1_1 to E1_6.

In this case, the power transmission side passive electrode E2 is omitted from the casing CB1 as shown in FIG. 15, and the power transmission device 10 is configured as shown in FIG.

According to FIG. 16, the switch circuit SW2 is formed by the switches SW2_11 to SW2_16. The connection destination of each of the switches SW2_11 to SW2_13 is switched between one end of the secondary winding Ns1, the other end of the secondary winding Ns1, and the open end. The connection destination of each of the switches SW2_14 to SW2_16 is switched between one end of the secondary winding Ns1, the other end of the secondary winding Ns1, and the ground. Further, the connection state of the switch circuit SW2 is controlled by the CPU 16.

Accordingly, one of the switches SW2_11 to SW2_16 is connected to one end of the secondary winding Ns, and the other one of the switches SW2_11 to SW2_16 is connected to the other end of the secondary winding Ns, and the remaining switches Is connected to the open end or ground.

DESCRIPTION OF SYMBOLS 10 ... Power transmission apparatus 14 ... PWM generation circuit 16 ... CPU
18 ...

Inverter

20, 32 ... Transformer E1-E2 ... Power transmitting electrode E3-E4 ... Power receiving electrode

Claims

A power transmission device provided along the first main surface of the first housing and provided with a first power transmission electrode and a second power transmission electrode to which an alternating voltage is applied, and provided along the second main surface of the second housing. A non-contact power transmission system formed by a power receiving device including a first power receiving electrode and a second power receiving electrode that are electrically coupled to the first power transmitting electrode and the second power transmitting electrode,
Each size of the first power transmission electrode and the first power reception electrode is the first power reception as viewed from a direction orthogonal to the second main surface in a specific state where the second main surface is opposed to the first main surface. An electrode is adjusted to fit within an outer edge of the first power transmission electrode;
The first power transmission electrode is divided into a plurality of partial electrodes by a notch, and the arrangement of the notch is adjusted so that a part of the second power receiving electrode faces the notch in the specific state. Contact power transmission system.
The non-contact power transmission system according to claim 1, wherein the notch is formed so that the plurality of partial electrodes are arranged in the first direction.
Each of the plurality of partial electrodes forms a strip extending in a second direction orthogonal to the first direction,
The non-contact power transmission system according to claim 2, wherein a maximum distance between two points assigned to an outline of the first power receiving electrode exceeds a distance corresponding to a sum of a width of the notch and a width of the strip.
The main surface of the second power receiving electrode is rectangular.
The second power transmission electrode has a rectangular opening for accommodating the first power transmission electrode;
4. The non-contact power transmission system according to claim 1, wherein a length of a short side of a rectangle forming the main surface of the second power receiving electrode is larger than a length of a short side of the rectangle forming the opening.
The main surface of the second power receiving electrode has a size covering the main surface of the first power receiving electrode,
5. The non-contact power transmission system according to claim 1, wherein the first power receiving electrode is stacked on the second power receiving electrode at a certain distance toward the outside of the second housing.
The second main surface has a size covered by the first main surface;
The said specific state presupposes the positional relationship in which the said 2nd main surface is settled in the outer edge of the said 1st main surface when it sees from the direction orthogonal to the said 2nd main surface. Non-contact power transmission system.
7. The apparatus according to claim 1, further comprising a selection unit that selects any one of the plurality of partial electrodes as an AC voltage application destination, and a control unit that controls an operation of the selection unit with reference to an impedance characteristic. A non-contact power transmission system according to crab.