POWER TRANSMISSION DEVICE AND POWER FEEDING SYSTEM

A power transmission device includes a power transmission circuit that includes a power transmission coil to transmit electric power to a power receiving coil of a power receiving device, a magnetic body that is magnetically coupled with the power transmission coil, and a moving device that changes a relative positional relationship between the magnetic body and the power transmission coil to change an impedance of the power transmission circuit such that the electric power is cut off or transmitted.

TECHNICAL FIELD

The present invention relates to a power transmission device and a power feeding system.

BACKGROUND ART

There is known a power feeding system that includes, for example, a power transmission device and a power receiving device (for example, PTL 1).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

For example, the power feeding system in PTL 1 does not have controlled the transmission or the cut off of the electric power from the power transmission device to the power receiving device. Accordingly, an increase in transmitted electric energy results in an increase in a current that is to be supplied to a power transmission circuit in the power transmission device, possibly causing damage to the power transmission circuit.

According to one or more embodiments of the present invention, a power transmission device includes a power transmission circuit that includes a power transmission coil to transmit electric power to a power receiving coil of a power receiving device, a magnetic body that is magnetically coupled with the power transmission coil, and a moving device that changes a relative positional relationship between the magnetic body and the power transmission coil to change an impedance of the power transmission circuit such that the electric power is cut off or transmitted.

Other features of one or more embodiments of the present invention will become apparent from the descriptions of the accompanying drawings and of the present specification.

According to one or more embodiments of the present invention, electric power supplied from a power transmission device to a power receiving device can be cut off or transmitted.

DETAILED DESCRIPTION OF EMBODIMENTS

At least the following matters will become apparent from descriptions of the present specification and of the accompanying drawings.

FIRST EXAMPLE

The following describes the power feeding system according to embodiments of the present invention with reference toFIG. 1toFIG. 3.FIG. 1is a transparent view illustrating the power feeding system according to one or more embodiments of the present invention. The casings25and35are indicated by dashed lines for the convenience of explanation.FIG. 2is a cross-sectional view illustrating the power feeding system according to one or more embodiments of the present invention.FIG. 2illustrates a cross section of a power feeding system100cut parallel to an X−Z plane along an approximate center of the power feeding system100inFIG. 1and viewed toward +Y (from the front to the back plane of the paper.)FIG. 3is a drawing illustrating the power feeding system according to one or more embodiments of the present invention.

The power feeding system100is a system that performs wireless power transmission using, for example, a resonance phenomenon in an electromagnetic field. A Z-axis is an axis along a vertical direction which is adjacent to the power transmission device2and the power receiving device3. A direction from the power transmission device2to the power receiving device3is defined as +Z while a direction from the power receiving device3to the power transmission device2is defined as −Z. An X-axis is an axis along a direction in which the moving devices281,284are arranged. A direction from the moving device281toward the moving device284is defined as +X while a direction from the moving device284toward the moving device281is defined as −X. A Y-axis is an axis orthogonal to the X-axis and the Z-axis. A direction from the front surface of the paper to the back surface of the paper is defined as +Y while a direction from the back plane of the paper to the front plane of the paper is defined as −Y.

The power feeding system100includes a power transmission device2and a power receiving device3.

The power transmission device2is a device that wirelessly transmits electric power to the power receiving device3.

The power receiving device3is a device that receives electric power output from the power transmission device2and supplies electric power according to the received electric power to a load31.

The load31is an electric power load such as an electrical device that operates based on the electric power supplied from the power receiving device3.

<Shape and Similar Specifications>

The power transmission device2includes a power transmission coil24, a casing25, a magnet26(second magnet), a magnetic body27, moving devices281,284, and an elastic device291(also called “electric power control mechanism”.) Here, the magnet26and the elastic device291correspond to the moving device. And the elastic device291corresponds to the elastic body.

The casing25houses a power transmission circuit200and the electric power control mechanism. The outer shape of the casing25has, for example, a columnar shape and is formed with, for example, an insulated material such as resin.

The power transmission coil24is tubularly wound around the winding shaft241, which is along the vertical direction (the Z-axis). The power transmission coil24has an opening243formed at substantially the center thereof through which the magnet26and the magnetic body27are inserted and taken out. For example, the power transmission coil24may have an opening similar to that of the opening243and may be housed in an insulated case that is along the outer shape of the power transmission coil24.

The moving devices281,284are secured to the bottom plate252of the casing25and support the power transmission coil24in a manner movable in the vertical direction. The moving device281includes a first member282and a second member283.

The first member282is in a cylindrical form and is formed with, for example, an insulated material such as resin. The lower end (−Z) of the first member282is secured to the bottom plate252.

The second member283is in a columnar shape and is formed with, for example, an insulated material such as resin. The upper end (+Z) of the second member283is secured to the lower portion (−Z) of the power transmission coil24. The outer diameter of the second member283is set to be smaller than the inner diameter of the first member282such that the second member283can be inserted inside the first member282. The second member283is moved upward (+Z) or downward (−Z) by using, for example, an actuator (not shown) disposed inside the first member282. This actuator is operated based on the driving force imparted by the servo motor51which is controlled by the control device4. In other words, the moving device281moves the power transmission coil24upward or downward by controlling the control device4. Description of the moving device284is omitted since the moving device284is similar to the moving device281.

The moving device281moves the power transmission coil24to a position at either the first height where the power transmission coil24reaches a vertical height of H1(FIG. 2) from the bottom plate252or the second height where the power transmission coil24reaches a vertical height of H2(FIG. 5) from the bottom plate252.

The magnetic body27is, for example, a cobalt or a ferrite for changing the impedance of the power transmission circuit200which includes the power transmission coil24. For example, the magnetic body27may be a coil being wound around a winding shaft which is along the Z axis. The magnetic body27is magnetically coupled with the power transmission coil24. The magnetic body27may be, for example, a ferromagnet. The magnetic body27is in a substantially columnar shape. The outer diameter of the magnetic body27is set to be smaller than the diameter of the opening243such that the magnetic body27can be moved into and out from the opening243of the power transmission coil24.

The magnet26is secured to the upper face (+Z) of the magnetic body27using, for example, adhesives such that the magnet26moves in the vertical direction together with the magnetic body27based on the magnetic force imparted by the magnet36(first magnet) of the power receiving device3. The outer diameter of the magnet26is set to be smaller than the diameter of the opening243such that the magnet26can be moved into and out from the opening243of the power transmission coil24. The magnet26is assumed to be magnetically placed such that the upper portion of the magnet26and the lower portion of the magnet36are homopolar so that the magnet26and the magnet36turn each other away. The magnet26may be formed with, for example, a material with a relative magnetic permeability lower than that of the magnetic body27such that, for example, effects on the changes in the impedance of the power transmission circuit200by the movement of the magnet26is kept relatively small.

The elastic device291elastically supports the magnetic body27and the magnet26in a vertically movable manner. The elastic device291is secured at the substantial center of the bottom plate252. Therefore, the magnetic body27would be disposed to include the winding shaft241of the power transmission coil24. The elastic device291includes a first member292and a second member293.

The first member292is in a cylindrical form and is formed with, for example, an insulated material such as resin. The lower end of the first member292is secured to the bottom plate252.

The second member293is in a columnar shape and is formed with, for example, an insulated material such as resin. The upper end of the second member293is secured to the lower face (−Z) of the magnetic body27. The outer diameter of the second member293is set to be smaller than the inner diameter of the first member292such that the second member293can be inserted inside the first member292. The second member293is biased from the lower side to the upper side by, for example, an elastic force of an elastic body such as a spring which is disposed inside the first member292.

The power transmission device2further includes a power supply21, an inverter22, a capacitor23, the control device4, the servo motor51, and a measuring device52.

The power supply21generates a DC power. The inverter22converts a DC power supplied from the power supply21into an AC power. The power transmission coil24is a primary side coil of the power feeding system100to wirelessly supply a power receiving coil34with electric power. The capacitor23is used to set the impedance of the power transmission circuit200.

One end of the power supply21is coupled to one end of the capacitor23via the inverter22. The other end of the power supply21is coupled to one end of the power transmission coil24via the inverter22. The other end of the power transmission coil24is coupled to the other end of the capacitor23. These couplings form the power transmission circuit200including the power supply21, the inverter22, the capacitor23, and the power transmission coil24.

The DC power output from the power supply21is converted from DC into AC by the inverter22and is supplied to the power transmission coil24. The AC power supplied to the power transmission coil24is supplied from the power transmission coil24to the power receiving coil34.

The measuring device52measures the current supplied to the power transmission coil24and transmits a cutoff signal to the control device4. For example, when a current with a value larger than a predetermined value is measured, the measuring device52transmits the cutoff signal. The predetermined value is, for example, a value to the extent of not damaging the power transmission device2. The predetermined value may be determined based on a specification or a similar condition of the power transmission device2.

The servo motor51imparts a driving power to the moving devices281,284for driving the moving devices281,284. The control device4controls the servo motor51.

When the control device4receives a cutoff signal, the control device4moves the power transmission coil24such that the electric power supplied from the power transmission coil24to the power receiving coil34is cut off in turn changing the impedance of the power transmission circuit200. Description of the control device4will be given later.

<Shape and Similar Specifications>

The power receiving device3includes the power receiving coil34, a casing35and the magnet36.

The casing35houses the magnet36and a power receiving circuit300which includes the power receiving coil34. The outer shape of the casing35has, for example, a columnar shape and is formed with, for example, an insulated material such as resin.

The power receiving coil34is wound around the winding shaft341, which is along the vertical direction (the Z-axis.) The power receiving coil34is secured to a predetermined position close to the lower side (−Z) inside the casing35.

The magnet36is in, for example, a substantially columnar shape. The outer diameter of the magnet36is set to be smaller than the inner diameter of the power receiving coil34such that the magnet36is secured inside the power receiving coil34. The magnet36is secured to the power receiving coil34using, for example, adhesives while in a state disposed inside the power receiving coil34.

<Circuit and Similar Components>

The power receiving device3further includes a rectifier circuit32and a capacitor33.

The power receiving coil34is a secondary side coil of the power feeding system100to which electric power is wirelessly supplied from the power transmission coil24. The rectifier circuit32converts an AC power supplied from the power receiving coil34into a DC power and supplies this converted DC power to the load31. The capacitor33is used to set a value of an impedance of the power receiving circuit300.

One end of the power receiving coil34is coupled to the load31via the capacitor33and the rectifier circuit32. The other end of the power receiving coil34is coupled to the load31via the rectifier circuit32. These couplings form the power receiving circuit300including the power receiving coil34, the capacitor33, the rectifier circuit32, and the load31.

===Electric Power Transmission and the Like===

The following describes the electric power transmission and the like according to one or more embodiments of the present invention with reference toFIG. 2toFIG. 5.FIG. 4is a cross-sectional view illustrating the power feeding system according to one or more embodiments of the present invention having a power receiving device disposed at a first position.FIG. 5is a cross-sectional view illustrating the power feeding system according to one or more embodiments of the present invention having a power transmission coil moved to a second height.FIG. 4andFIG. 5illustrate cross-sectional views similar to that ofFIG. 2.

When the power transmission device2transmits electric power to the power receiving device3, the power receiving device3is disposed at the first position. As illustrated inFIG. 4, the first position is a position where an opposed surface351of the power receiving device3and an opposed surface251of the power transmission device2are in contact.

When the power receiving device3is moved from the second position to the first position, which is to be described later, a magnetic force is imparted from the magnet36to the magnet26in the downward direction (−Z) which is in a direction opposite the upwardly directed (+Z) elastic force which is imparted from the elastic device291to the magnetic body27. The magnet26and the magnetic body27are moved to the lower side (−Z) based on the magnetic force which works against the elastic force. The elastic force here is set such that the magnet26and the magnetic body27are disposed at a position where the magnet26is encircled by the power transmission coil24while the magnetic body27is not encircled by the power transmission coil24, when the power transmission coil24is disposed at the first height and the power receiving device3is disposed at the first position as well. The relative positional relationship among the power receiving coil34, the power transmission coil24and the magnetic body27illustrated inFIG. 4is also called the first positional relationship.

<Case when Electric Power is Not Transmitted>

When the power transmission device2does not transmit electric power to the power receiving device3, the power receiving device3is disposed at a second position. As illustrated inFIG. 2, the second position is a position where the power receiving device3is apart from the power transmission device2. In other words the second position is a position where the power receiving device3is farther distant from the power transmission coil24than when at the first position. And the second position is a position where the magnetic force of the magnet36is not imparted to the magnet26.

A magnetic force would not be imparted from the magnet36to the magnet26when the power receiving device3is moved from the first position to the second position. The magnet26and the magnetic body27are moved upward (+Z) by the elastic force. The elastic force here is set such that the magnet26and the magnetic body27are disposed so that the magnet26is not encircled by the power transmission coil24and the magnetic body27is encircled by the power transmission coil24, when the power transmission coil24is disposed at the first height and the power receiving device3is disposed at the second position. The relative positional relationship among the power receiving coil34, the power transmission coil24and the magnetic body27illustrated inFIG. 2is also called the second positional relationship.

<Case when Cutting Off Transmitted Electric Power>

The power transmission coil24is moved from the first height to the second height when cutting off the electric power transmitted from the power transmission device2to the power receiving device3. In this case, the relative positional relationship among the power receiving coil34, the power transmission coil24and the magnetic body27is the positional relationship illustrated inFIG. 5. This positional relationship is also called the third positional relationship.

===Settings of Power Transmission Device and Power Receiving Device===

The following describes the settings of the power transmission device and the power receiving device according to one or more embodiments of the present invention with reference toFIG. 2andFIG. 4toFIG. 6.FIG. 6is a drawing illustrating a relationship between a frequency and transmitted electric power according to one or more embodiments of the present invention. The frequency inFIG. 6indicates the frequency of the electric power output from the power transmission coil24. And the transmitted electric power indicates the electric power transmitted from the power transmission coil24to the power receiving coil34. The transmitted electric power here is determined based on, for example, the transmission efficiency and the like of the electric power transmitted from the power transmission coil24to the power receiving coil34.

The power transmission device2and the power receiving device3are set based on the transmission efficiency. Settings of the power transmission device2and the power receiving device3include, for example, setting the frequency of the electric power transmitted from the power transmission device2and impedances of the power transmission circuit200and the power receiving circuit300.

As described above, the transmission efficiency is determined based on a resonant frequency or a similar condition. These resonant frequencies f1and f2are, for example, determined based on Expression (1) to Expression (3).

L indicates the value of the inductance of the power transmission circuit200and C indicates the capacitance value of the power transmission circuit200. k indicates a coupling coefficient between the power transmission coil24and the power receiving coil34.

The value of the coupling coefficient k changes according to a transmission distance D, which indicates a distance between the power transmission coil24and the power receiving coil34. Alternatively, a unique resonant frequency f0varies according to the value of the inductance of the power transmission circuit200. That is, the resonant frequencies f1and f2, namely, the transmission efficiency varies according to the transmission distance D and the value of the inductance of the power transmission circuit200. Accordingly, varying the transmission distance D and the inductance of the power transmission circuit200ensures transmitting or cutting off electric power from the power transmission device2to the power receiving device3.

<Settings of Power Transmission Device and Power Receiving Device>

The power transmission device2and the power receiving device3are configured such that electric power is transmitted when the relative positional relationship among the power receiving coil34, the power transmission coil24and the magnetic body27is in a first positional relationship and electric power is not transmitted when the relative positional relationship among the power receiving coil34, the power transmission coil24and the magnetic body27is in the second and third positional relationships.

The following describes the control device according to one or more embodiments of the present invention with reference toFIG. 7andFIG. 8.FIG. 7is a drawing illustrating hardware of the control device according to one or more embodiments of the present invention.FIG. 8is a drawing illustrating functions of the control device according to one or more embodiments of the present invention.

The control device4includes a Central Processing Unit (CPU)41, a communications device42, a storage device43, a display device44, and an input device45. The CPU41executes a program stored in the storage device43to achieve various functions of the control device4and to integrally control the control device4. The storage device43stores the above-described programs and various pieces of information. The display device44is a display to display information on the control device4. The input device45is, for example, a keyboard and a computer mouse to input information to the control device4. The communications device42performs communications between the servo motor51and the measuring device52.

The control device4further includes a detecting unit46and a control unit47(also referred to as “various functions of the control device4”). The execution of the program stored in the storage device43by the CPU41achieves the various functions of the control device4.

When the detecting unit46receives the cutoff signal, the detecting unit46detects an abnormality in the power transmission device2. The measuring device52may transmit the cutoff signal to the control device4. Alternatively, a user of the power feeding system100may transmit the cutoff signal to the control device4via the input device45.

The control unit47moves the power transmission coil24to the first height or the second height based on the results detected by the detecting unit46.

===Operations of Power Feeding System===

The following describes the operations of the power feeding system according to one or more embodiments of the present invention with reference toFIG. 2,FIG. 4, andFIG. 5.

<When Electric Power is not Transmitted (FIG. 2)>

When the power transmission device2does not transmit electric power to the power receiving device3, the power receiving device3is disposed at the second position. The relative positional relationship among the power receiving coil34, the power transmission coil24and the magnetic body27becomes the second positional relationship, and deteriorates the transmission efficiency and enters the power receiving device3in a state where the electric power is not transmitted.

<When Electric Power is Transmitted (FIG. 4)>

When the power transmission device2transmits electric power to the power receiving device3, the power receiving device3is disposed at the first position. Further, in this case, the power transmission coil24is moved to the first height. The relative positional relationship between the power receiving coil34, the power transmission coil24and the magnetic body27becomes the first positional relationship, and the electric power is transmitted with improved transmission efficiency.

<When Transmitted Electric Power is Cut off (FIG. 5)>

When electric power is cut off while the power transmission device2transmits this electric power to the power receiving device3, the power transmission coil24is moved from the first height to the second height. The relative positional relationship among the power receiving coil34, the power transmission coil24and the magnetic body27becomes the third positional relationship, and the transmission efficiency deteriorates and the electric power is cut off.

SECOND EXAMPLE

The power feeding system100B according to one or more embodiments of the second example of the present invention has the power transmission device2in the power feeding system100according to one or more embodiments of the first example changed to a power transmission device2B.

The following describes the power feeding system according to one or more embodiments of the present invention with reference toFIG. 9andFIG. 10.FIG. 9is a cross-sectional view illustrating the power feeding system according to one or more embodiments of the present invention having a power receiving device provided at the first position.FIG. 10is a cross-sectional view illustrating the power feeding system according to one or more embodiments of the present invention having the power transmission coil moved to the second height. Parts inFIGS. 9 and 10same as those inFIGS. 4 and 5are designated like reference characters used inFIGS. 4 and 5.

The power feeding system100B includes the power transmission device2B. The casing25B of the power transmission device2B includes oblong holes253,254which communicate from the inside of the casing25B to the outside thereof. The oblong holes253,254are provided vertically to the side face of the casing25B such that the projections243,244can be moved in the vertical direction (Z axis.)

The projections243,244are used to cut off the electric power transmitted from the power transmission device2B to the power receiving device3by, for example, the user manually moving the power feeding system100B. The projections243,244are secured to the outer side face of the power transmission coil24.

Electric power is transmitted when the relative positional relationship among the power receiving coil34, the power transmission coil24and the magnetic body27becomes the first positional relationship (FIG. 9) by the user manually moving the power feeding system100B. When the relative positional relationship among the power receiving coil34, the power transmission coil24and the magnetic body27becomes the third positional relationship (FIG. 10) by the user manually moving the power feeding system100B, while electric power is being transmitted, the electric power would be cut off. In other words, the electric power can be transmitted or cut off by a manual operation.

The power receiving device3B is disposed at the first position when electric power is transmitted from the power transmission device2to the power receiving device3B. Further in this case, the power transmission coil24is moved to the first height. The relative positional relationship among the power receiving coil34, the power transmission coil24and the magnetic body27becomes the first positional relationship, and the electric power is transmitted with improved transmission efficiency.

<When Transmitted Electric Power is Cut off (FIG. 10)>

When electric power is cut off during the power transmission device2transmitting this electric power to the power receiving device3, the power transmission coil24is moved from the first height to the second height based on the moving force imparted to the projections243,244. The relative positional relationship between the power receiving coil34, the power transmission coil24and the magnetic body27becomes the third positional relationship, and the transmission efficiency deteriorates and the electric power is cut off.

As described above, the power transmission device2(embodiments of the first example) includes the power transmission circuit200, the magnetic body27, and the moving devices281,284. The power transmission circuit200includes the power transmission coil24to transmit electric power to the power receiving coil34of the power receiving device3. The magnetic body27is magnetically coupled with the power transmission coil24. The moving devices281,284change the relative positional relationship between the magnetic body27and the power transmission coil24to change the impedance of the power transmission circuit200such that the electric power is cut off or supplied. Accordingly, the electric power supplied from the power transmission device2to the power receiving device3can be cut off or transmitted. This ensures preventing the power transmission device2from being damaged by supplying a current exceeding a rated current to the power transmission circuit200. This ensures improving safety of the power feeding system100.

The moving devices281,284move the power transmission coil24to cut off the electric power upon reception of the cutoff signal for cutting off the electric power. Hereby the electric power is automatically cut off based on the cutoff signal. Thus the safety of the power feeding system100can be improved.

The magnetic body27is disposed to include the winding shaft241of the power transmission coil24. The moving devices281,284move the power transmission coil24along the winding shaft241. Thus the amount of impedance of the power transmission circuit200changed by the moving of the power transmission coil24can be increased to certainly cut off the electric power.

Further, the magnetic body27is formed such that the outer diameter of the magnetic body27is smaller than the inner diameter of the power transmission coil24. The moving devices281,284move the power transmission coil24such that the state of the magnetic body27being encircled by the power transmission coil24is shifted to the state of the magnetic body27not being encircled by the power transmission coil24, or vice versa. Thus the amount of impedance of the power transmission circuit200changed by the moving of the power transmission coil24can be further increased to further certainly cut off the electric power.

The magnet26and the elastic device291as the moving device move the magnetic body27to transmit or cut off the electric power according to the position of the power receiving device3. Hereby, the electric power can be transmitted or cut off without performing, for example, on-off switching to control the transmission or cut off of the electric power. Thus a power transmission device2which is easy to use can be provided.

The power receiving device3includes the magnet36. The magnet26of the power transmission device2is secured to the magnetic body27such that the magnet26moves together with the magnetic body27based on the magnetic force imparted by the magnet36. The elastic device291imparts to the magnetic body27an elastic force which is in a direction opposite the direction of the aforementioned magnetic force. The elastic force of the elastic device291is set such that the magnetic body27moves in the downward direction (−Z) based on the magnetic force which works against the elastic force in order to transmit the electric power when the power receiving device3is disposed at the first position, and the magnetic body27moves upward (+Z) based on the elastic force in order to cut off the electric power when the power receiving device3is disposed at the second position that does not allow transmission of the electric power and that is apart from the power transmission coil24compared to the first position. Thus the magnetic body27can be moved using a relatively simple mechanism including the magnet26and the elastic device291. Hereby, for example, this eliminates the need for disposing a distance sensor and the like which detects the distance between the power transmission device2and the power receiving device3in turn reducing the manufacturing cost of the power transmission device2. Additionally, a power source for moving the magnetic body27is needless so that a power transmission device2which is easy to use can be provided.

The magnet26is secured to the magnetic body27such that the magnet26is arranged side by side with the magnetic body27along the moving direction (Z axis) of the magnetic body27. Thus the electric power can be certainly transmitted or cut off by certainly moving the magnetic body27along the moving direction.

The magnetic body27is, for example, a ferrite. Thus, the relative magnetic permeability of the magnetic body27can be improved to increase the amount of changes in the impedance of the power transmission circuit200.

The magnetic body27is, for example, a coil. Thus, the weight of the magnetic body27can be reduced. And the relative magnetic permeability of the magnetic body27can be relatively easily adjusted by changing the number of turns in the coil.

One or more embodiments of the first and second examples are intended for easy understanding of the present invention and are not in any way to be construed as limiting the present invention. Embodiments of the present invention may be modified and improved without departing from the scope of the invention, and equivalents thereof are also encompassed by the invention.

One or more embodiments of the first example describes that the elastic device291imparts an elastic force to the magnetic body27. However, this should not be construed in a limiting sense. For example, the elastic force may be directly imparted to the magnetic body27with a spring and the like.

One or more embodiments of the first example also describes that the power transmission device2and the power receiving device3are configured such that electric power is transmitted when in the first positional relationship and electric power is not transmitted when in the second and the third positional relationships. However, this should not be construed in a limiting sense. For example, the power transmission device2and the power receiving device3may be configured such that electric power is transmitted when in the third positional relationship and electric power is not transmitted when in the first positional relationship. In this case, the power transmission coil24may be moved from the second height to the first height such that the third positional relationship is changed to the first positional relationship when cutting off the electric power being transmitted from the power transmission device2to the power receiving device3.

REFERENCE SIGNS LIST