JP7131815B2 - Wireless power transmission coil unit - Google Patents

Description

The present disclosure relates to a wireless power transmission coil unit for contactless power supply that can transmit power in a contactless manner.

2. Description of the Related Art In recent years, the use of an electromagnetic induction wireless power supply device has been studied for charging batteries of vehicles such as electric vehicles and hybrid vehicles. In a wireless power supply device, a power transmission coil is energized with a high-frequency alternating current (approximately several 10 kHz to 200 kHz), and a power reception coil receives a high-frequency magnetic field generated from the power transmission coil, thereby transmitting power in a contactless manner.

In such a contactless power supply device, the use of a spiral planar coil having a rectangular cross-section has been conventionally studied in response to the thinning of the device. In addition, a magnetic shield made of ferrite or the like is placed in the vicinity of the coil in order to avoid abnormal heat generation due to eddy currents generated in surrounding metal parts due to a high-frequency magnetic field (for example, Patent Document 1). Thus, the transmission coil unit is composed of a combination of planar coils and magnetic shields.

Generally, in a transmission coil unit, when the coil is energized, magnetic lines of force are generated so as to surround the cross section of the coil. Also, since the magnetic shield has a high magnetic permeability, the magnetic lines of force are distributed so as to flow vertically from the surface of the magnetic shield. The coil is wound with a plurality of conductors (coil conductors), and the coil conductors are close to each other. Therefore, the coil has both the skin effect due to the current flowing through it and the proximity effect due to the eddy currents generated in the adjacent coil conductors. Therefore, the current flowing through each coil conductor is biased inside the conductor, especially the inner circumference of the coil conductor and the outer circumference of the coil conductor. As a result, currents and magnetic lines of force concentrate at those parts.

In particular, the coil disclosed in Patent Literature 1 has a thin high-frequency skin because the rectangular cross-section is flat, and the current flows intensively in the thin portion. As a result, copper loss occurs and the AC resistance increases, resulting in a decrease in power transmission efficiency. In a single coil or inductor that does not emit magnetic flux, copper loss can be reduced by narrowing the width of the coil conductors on the inner and outer circumferences of the coil and widening the width of the conductor on the middle circumference according to the crossover magnetic flux density. (Patent Document 3). However, when using a coil with such a configuration for wireless power transmission, it is necessary to consider the influence of magnetic shields placed facing each other.

In order to solve such a problem, it is known to use a litz wire obtained by twisting a large number of insulated wires as a coil winding (for example, Patent Document 3). A litz wire is a wire obtained by twisting a large number (eg, 500 or more) of fine wires (eg, enameled wires with a wire diameter of 0.1 mm or less), and can suppress high-frequency loss due to the skin effect and proximity effect.

Japanese Unexamined Patent Application Publication No. 2013-201296 JP-A-11-40438 JP 2016-219252 A

However, the litz wire has a problem that the manufacturing cost is high because the wires are thin and the number of wires is large. Therefore, in view of the above circumstances, the present invention reduces the high frequency loss (copper loss) due to the skin effect and proximity effect of the planar spiral coil, suppresses the increase in AC resistance, and can be manufactured at low cost. An object of the present invention is to provide a transmission coil unit of

A transmission coil unit for contactless power supply according to one aspect of the present disclosure is a wireless power transmission coil unit including a spirally wound planar coil and a magnetic shield provided facing the coil. and the gap between the coil conductor of any winding positioned in the middle circumference of the coil and the coil conductor of the winding adjacent thereto is the coil conductor of any winding positioned on the inner circumference side or the outer circumference side of the coil. and the coil conductors of any windings that are narrower than the gap between and the coil conductors of the adjacent windings and are located at least on the inner and outer circumferences of the coil and the coil conductors of the windings adjacent to them In the gap, a magnetic body is provided so as to protrude from the coil on the side opposite to facing the magnetic shield, and on a part of the surface of the coil on the side opposite to the magnetic shield A magnetic body is provided .

A magnetic body may be provided on the entire surface of the coil facing the magnetic shield.

The magnetic material may be unevenly distributed on the inner peripheral side of a coil of arbitrary windings on the inner peripheral portion of the coil, and on the outer peripheral side of a coil of arbitrary windings on the spiral outer peripheral portion.

According to one aspect of the present disclosure, it is possible to reduce the number of magnetic lines of force penetrating the coil conductor by inducing the magnetic flux lines concentrated on the surface and side surfaces of the spiral coil conductor on the flat plate to the magnetic layer. It is possible to reduce the AC resistance (copper loss) of the coil by suppressing the eddy current of the coil, and it is possible to obtain a transmission efficiency that is almost equal to or higher than that when using a litz wire.

Top view and cross-sectional view of a typical spiral coil unit Sectional view of the wireless transmission coil unit according to the first embodiment of the present disclosure Sectional view of the wireless transmission coil unit of the second embodiment of the present disclosure An enlarged cross-sectional view of a wireless transmission coil unit according to a second embodiment of the present disclosure Explanatory diagram showing the effect of the magnetic material in the wireless transmission coil unit Sectional view of the wireless transmission coil unit of Example 1 of the present disclosure Configuration diagram of the litz wire coil unit on the power receiving side Configuration diagram of power transmission side litz wire coil unit Analysis model diagram of the wireless transmission coil unit in the second embodiment of the present disclosure Magnetic flux and current distribution diagram of copper plate coil in Embodiment 2 of the present disclosure Magnetic flux and current distribution diagram of MPC coil in Embodiment 2 of the present disclosure Dimensional drawing of the MPC coil in Example 2 of the present disclosure Electrical characteristics of various coils in Example 3 of the present disclosure Transmission Efficiency of Various Coil Units in Example 4 of the Present Disclosure

Hereinafter, embodiments according to one aspect of the present disclosure will be described in detail with reference to the drawings.

First, FIG. 1 shows the configuration of a general planar spiral coil type wireless transmission coil unit. It is characterized in that a spiral coil conductor (Copper) and a magnetic shield (Ferrite) are provided facing each other. In FIG. 1, the portion surrounded by a broken line square is a radial cross-sectional view, and the structural features of the wireless transmission coil unit will be described below with such a radial cross-sectional view in the present embodiment.

FIG. 2 is a cross-sectional view of the wireless transmission coil unit according to the first embodiment of the present disclosure. In FIG. 2, 1 is a magnetic shield, which is made of a magnetic material such as ferrite. Reference numeral 2 denotes a coil, which is made by forming a coil conductor (2a) of copper, aluminum, or the like into a spiral shape and a plate shape. As a manufacturing method, it may be made by cutting a single metal plate into a spiral shape by pressing or etching, or by casting, or by winding a belt-shaped conductor on a plane. good too. Although the magnetic shield 1 and the coil 2 are not in direct contact with each other, a non-magnetic insulating material (resin, ceramic, etc.) may be interposed therebetween (not shown).

In FIG. 2, the gap 2d between the coil 2c of an arbitrary winding located in the middle circumference of the spiral coil and the coil of the winding adjacent thereto is the coil conductor of the arbitrary winding on the inner circumference side and the outer circumference side of the coil. (2a, 2e) and the gaps (2b, 2f) between the coil conductors of the respective adjacent windings. In the present embodiment, the inner circumference refers to an area from the innermost to N/2 turns from the innermost to the outermost when the number of turns of the coil 2 is N (N>8), and the outer circumference refers to the area from the outermost. Refers to the area from 1 to N/3 turns inside. The middle circumference refers to the area surrounded by the inner circumference and the outer circumference.

By configuring the coil 2 as described above, it is possible to control the path along which the lines of magnetic force pass so as to reduce the copper loss. In general, in a coil unit having a magnetic shield 1 on its back surface, arcuate lines of magnetic force are generated from the coil 2 from the inner circumference to the outer circumference. That is, as shown in FIG. 5A, while passing through the magnetic shield (Ferrite), magnetic lines of force are generated upward on the inner circumference, horizontally (parallel to the coil) on the middle circumference, and downward on the outer circumference.

Therefore, in the vicinity of the middle circumference where the lines of magnetic force are horizontal, it is better to narrow the gap (2b) between the adjacent coil conductors as much as possible so that the magnetic flux does not change its direction toward the magnetic shield 1 (in the vertical direction) and is parallel to the coil 2 as it is. Prone. On the other hand, on the inner and outer peripheral sides of the coil where the magnetic lines of force include vertical components, the gaps (2b and 2f) are widened as much as possible so that the lines of magnetic force do not intersect the coil conductors as much as possible. It is better to release a large amount of magnetic flux to the magnetic shield 1 side.

As described above, in the present embodiment, the gap 2d between the coil 2c of an arbitrary winding located in the intermediate circumference and the coil of the winding adjacent thereto is formed by the arbitrary windings on the inner and outer circumferences. By making the gaps (2b, 2f) between the coil conductors (2a, 2e) and the coil conductors of the adjacent windings narrower than the gaps (2b, 2f), the magnetic lines of force generated in an arc shape from the inner circumference to the outer circumference of the coil are efficiently magnetically shielded. 1, and as a result, the magnetic flux interlinking with the coil conductor can be reduced, and as a result, copper loss due to eddy currents can be reduced.

In adjusting the gaps 2b, 2d and 2f, a method of changing the widths of the coil conductors 2a, 2c and 2e is employed in FIG. 2, but the present embodiment is not limited to this method. The width of the coil conductor may be made uniform and the winding pitch may be changed.

A second embodiment of the present disclosure will be described below. FIG. 3 is a cross-sectional view of a wireless transmission coil unit according to a second embodiment of the present disclosure; 3, the magnetic shield 1 and the coil 2 have the same functions as those shown in FIG. In the present embodiment, magnetic bodies 3 (3a, 3b, 3c) are provided in at least the gaps 2b, 2d, 2f on the inner and outer peripheral sides of the coil 2 and their surroundings. The magnetic body 3 may be a composite magnetic material in which magnetic powder is kneaded into resin, which is an insulating material.

4 is a partially enlarged view of FIG. 3. FIG. First, magnetic bodies 3b are provided in gaps 2b between coil conductors 2a of arbitrary windings on at least the inner and outer circumferential sides and coil conductors of adjacent windings. This magnetic body 3b reduces the interlinking magnetic flux by inducing the magnetic flux linking the coil 2 to the left and right with the wall of the magnetic body.

A magnetic body 3a is provided on the entire surface of the coil 2 facing the magnetic shield 1 (hereinafter also referred to as the lower surface of the coil). The magnetic body induces the magnetic flux attracted to the magnetic shield to the magnetic body, thereby reducing the magnetic flux interlinking with the upper part of the coil and the ends of the coil.

The magnetic body 3 in the gap portion of the coil 2 except for the middle portion is provided on the side opposite to the magnetic shield 1 so as to protrude from the upper surface of the coil conductor 2a. Further, a magnetic body 3c is provided on a part of the surface of the coil conductor opposite to the magnetic shield 1 (hereinafter also referred to as the upper surface of the coil). The magnetic bodies are unevenly distributed so as to cover only the inner circumference side of the coil conductor 2a on the inner circumference, and to cover only the outer circumference side of the coil conductor on the outer circumference.

With the above configuration, the magnetic flux interlinking with the coil can be reduced as much as possible, and the bias of the current in the coil conductor due to the proximity effect can be reduced. It is possible to reduce the loss even more than that.

Configuration examples of the wireless transmission coil units in the first and second embodiments and results of analysis and simulation will be described in the following examples.

First, FIG. 5(a) shows a cross section of a wireless transmission coil unit (FIG. 1) having a general structure, a current flowing therethrough, and a schematic diagram of magnetic force generated therefrom. In FIG. 5, ferrite is used as the magnetic shield 1, and copper is used as the coil conductor 2a. As shown in FIG. 5A, the lines of magnetic force pass through the magnetic shield and form an arc from the inner circumference side to the outer circumference side of the coil. In the cross section of the coil conductor (Copper), the cross-marked symbol in the circle means the current flowing downward from the top of the paper through the conductor. This current is biased according to the magnetic lines of force penetrating the coil conductor. In other words, the current concentrates at the corners of conductors where magnetic lines of force obliquely intersect (closer to the outer circumference of the inner circumference, closer to the inner circumference of the outer circumference). In addition, the magnetic flux is attracted to the ferrite, so that the current tends to be biased toward the upper part of the coil.

Here, when a magnetic wall is provided in the gap sandwiched between the coil conductors (FIG. 5(b)), the flow of the lines of magnetic force changes, and the current distribution changes accordingly. In other words, in the inner and outer windings of the coil, the current is biased toward the ends and upper portion of the coil. In addition, the current flowing through the windings in the middle circumference of the coil tends to be biased towards the upper part of the coil.

Therefore, as shown in the second embodiment, if a magnetic material is provided at the unevenly distributed position on the upper surface of the coil (FIG. 5(c)), the deviation of the ends can be reduced. Furthermore, by providing a magnetic material on the entire lower surface of the coil (the side facing the magnetic shield 1) and passing the magnetic flux attracted to the magnetic shield 1 (ferrite) through this magnetic material, the current in the inner and outer windings of the coil is increased. It will flow not only to the top but also to the sides. By controlling the flow of the magnetic flux using the magnetic material in this way, the copper loss can be reduced and the bias of the current can be suppressed.

(Embodiment 1) Structure of Wireless Transmission Coil Unit FIG. 6 shows the specific structure of the power receiving side of the wireless transmission coil unit (hereinafter referred to as MPC (Magnetic Path Control) coil unit) of the second embodiment. be. In FIG. 6, (a) is a plan view, (b) is a sectional view, and (c) is a structural drawing. The coil 2 (Coil) has a spiral shape and the number of turns N=10. In addition, a ferrite (magnetic shield 1) is provided on the back surface of the coil to reduce the radiated electromagnetic field. The copper plate (coil conductor 2a) has a thickness of 1.5 mm, and magnetic bodies (3b, 3c) are provided between the coil windings and at the portions where the current density is uneven. A magnetic material (3a) was also used for the lower part of the coil. The gap between the magnetic material under the coil and the ferrite is 3 mm, and the thickness of the ferrite is 5 mm.

(Comparative Example 1) Structure of Wireless Transmission Coil Unit Using Litz Wire Coil FIG. 7 shows the structure of a power receiving side coil unit (hereinafter referred to as LCW coil) using a litz wire as a coil. 7(a) is a plan view, (b) is a sectional view, and (c) is a structural drawing. The number of turns N=10, which is the same as the MPC coil unit of the first embodiment. In addition, ferrite and an aluminum plate are used to reduce the radiated electromagnetic field. The LCW coil wire is made by twisting 4200 copper wires with a conductor diameter of 0.05 mm in stages (Fig. 7(c)). The finished outer diameter is 5 mm.

FIG. 8 shows the structure of the LCW coil on the power transmission side, with FIG. 8(a) showing a plan view and FIG. 8(b) showing a cross-sectional view. The overall shape is longer than the power receiving side, but the litz wire used is the same as the power receiving side coil.

ここで、Ｑ_１：送電コイルのＱ値、Ｑ_２：受電コイルのＱ値、Ｕ：性能指標、η_ｃ：伝送効率（％）とする。 (Example 2) Magnetic Field Analysis of Coil Unit In this example, a two-dimensional AC magnetic field analysis (Ansys Maxwell) was used to analyze the coil unit for wireless transmission. Furthermore, the resistance R, inductance L, and Q value of the receiving coil were calculated from the magnetic field analysis results. Also, the mutual inductance M was calculated from the three-dimensional AC magnetic field analysis, and the transmission efficiency η _c was calculated from these values using the following equations (1) to (4). Table 1 shows the analysis conditions. A magnetic composite material using amorphous powder is applied to the magnetic material 3 used for the coil.

Here, Q ₁ is the Q value of the power transmitting coil, Q ₂ is the Q value of the power receiving coil, U is the performance index, and η _c is the transmission efficiency (%).

FIG. 9 shows an analysis model in a two-dimensional cylindrical coordinate system. Although the actual shape of the coil is square, the analysis is performed in a cylindrical coordinate system. Therefore, the wire length and pitch of the coil are set to be the same, and the analysis is performed in a circular shape. 10 and 11 show analysis in a two-dimensional cylindrical coordinate system. FIG. 10 shows the type of the first embodiment in which the gap in the middle circumference of the coil is narrowed (hereinafter referred to as a copper plate coil), and FIG. (MPC coil) is simulated.

The dimensions of the coil used for the magnetic field analysis will be explained below. The total number of turns was N=10, and the pitch between the coil conductors was 7 mm. The gap between the coil conductors in the inner circumference (5 turns from the innermost circumference to the outside) was set to 2.2 mm. For the outer circumference (up to two turns inward from the outermost circumference), the gap between the outermost circumference (first winding) and the second winding is 2.2 mm, and the second and third windings (between the middle circumference and border) was set to 1.2 mm.

Further, FIG. 10 (copper plate coil model) shows the simulation results of the magnetic lines of force and the current distribution. The lines of magnetic force are perfectly parallel at the middle circumference of the coil, but the magnetic flux interlinks perpendicularly to the plane of the coil on the inner and outer circumferences of the coil. As a result, the current is biased to the left and right. The current distribution is indicated by shading in the drawing. For example, a whitish portion in the coil conductor is a portion where a large amount of current flows. Although the lines of magnetic force are parallel even in the middle portion of the coil, they are interlinked in parallel with the coil conductor.

FIG. 11 shows a simulation result of an MPC coil in which a magnetic material is provided in the gap between the coils in FIG. 10 and around it. In this embodiment, the height at which the magnetic material protrudes from the upper surface of the coil is set to 1 mm, and the thickness of the magnetic material covering the entire lower surface of the coil is set to 0.5 mm. The length of the magnetic material partially covering the upper surface of the coil was set to 0.4 mm to 0.6 mm. Details of the shape and dimensions of the magnetic body are shown in FIG.

In the MPC coil (Fig. 11), the magnetic flux that interlinks perpendicularly to the plane of the coil inside and outside the coil winding is induced to the left and right by the walls of the magnetic material, thereby suppressing the interlinkage with the coil conductor as much as possible. there is In addition, since the magnetic material is used in places such as the ends of the coil where the current is largely biased, the interlinkage magnetic flux is also reduced. However, since the magnetic flux interlinks parallel to the coil plane at the center of the coil winding, the current is biased to the upper part of the coil. However, by using a magnetic material on the lower surface of the coil, the magnetic flux attracted to the ferrite is guided to the magnetic material, and the magnetic flux interlinking with the upper part of the coil and the ends of the coil is reduced.

(Example 3) Impedance Characteristics of Coil Unit In this example, the impedance characteristics of the coil units shown in FIG. 10 (copper plate) and FIG. 11 (MPC) were calculated using electromagnetic field analysis. For comparison, the impedance of the LCW coil and the power transmission coil was also measured using an impedance analyzer (Agilent Technologies 4294A). Coupling coefficient k was measured under the condition of transmission distance l=150 mm. The inductance La in the in-phase series connection of the coils and the inductance Lb in the reverse-phase connection were measured, and the mutual inductance M was calculated. Also, the coupling coefficient k of the coil was calculated from the inductance L1 of the power transmitting coil, the inductance L2 of the power receiving coil, and the mutual inductance M. A performance index U of the coil was calculated using the measured coupling coefficient k and the Q value of the coil. Finally, the transmission efficiency η _c was calculated from the performance index U. FIG. 13 shows the impedance characteristics of each coil unit.

In FIG. 13(a), the resistances at 85 kHz of the copper plate coil, MPC coil, LCW coil, and transmission coil are shown as 187.4 mΩ, 80.2 mΩ, 32.6 mΩ, and 29.5 mΩ, respectively. By applying the magnetic flux path control technology of the second embodiment to a general copper plate coil unit, the resistance value was reduced from 187.4 mΩ to 80.2 mΩ (FIG. 13(b)). At this time, the inductances at 85 kHz of the copper plate coil unit, the coil unit of the second embodiment, the LCW coil unit, and the power transmission coil unit were 40.1 μH, 43.6 μH, 37.7 μH, and 40.3 μH, respectively. Note that although the power transmission coil has a smaller number of turns than the power reception coil, it has a larger outer diameter and therefore has a larger inductance than the LCW for power reception. The coil unit of the second embodiment has the effect of suppressing the bias of the current density, so the inductance is slightly increased compared to the copper plate coil.

FIG. 13(c) shows the Q values at 85 kHz of the copper plate coil unit, the MPC coil unit, the LCW coil unit, and the power transmission coil unit. They were 114, 290, 610 and 724, respectively. Since the MPC coil has half the resistance and improved inductance compared to the copper plate coil, the Q value increases 2.5 times.

Table 2 summarizes the impedance characteristics, coupling coefficient k, and transmission efficiency η shown in FIG. Coupling coefficients and efficiencies are discussed in more detail. FIG. 14 shows the transmission efficiency of the coil in which the figure of merit U (formula (3)) is plotted on the horizontal axis. First, electromagnetic field analysis software (Maxwell 3D) was used to calculate the mutual inductance between the copper plate coil and the MPC coil, and the coupling coefficient was calculated from equation (2). Further, the inductance La in the in-phase series connection and the inductance Lb in the opposite-phase connection of the LCW coil and the power transmission coil were measured, and the mutual inductance M was calculated using the formula (1).

The coupling coefficients of the copper plate coil, MPC coil, and LCW coil were 0.102 (measured value), 0.125 (calculated value), and 0.175 (calculated value), respectively. Since the magnetic material used for the MPC coil induces the magnetic flux from the power transmitting coil to the power receiving coil, the coupling coefficient k of the MPC coil is higher than that of the copper plate coil. It is considered that the magnetic flux interlinking with the current is increased and the coupling coefficient k is improved by suppressing the deviation of the current and allowing the current to flow through the coil surface.

As shown in FIG. 14, the efficiencies in the copper plate coil, MPC coil, and LCW coil were 94.58% (analysis value), 97.54% (analysis value), and 97.29% (measurement value), respectively. Compared to copper plate coils, MPC coils use magnetic flux path control technology to reduce copper loss and reduce resistance R. In addition, since the bias of the current density was suppressed, the inductance increased, and as a result, the Q value improved. The MPC coil has the effect of inducing magnetic flux to the receiving coil and has a high coupling coefficient compared to the copper plate coil. Therefore, the efficiency of the copper plate coil is 94.58%, whereas the efficiency of the MPC coil is 97.54%, which is an improvement of 2.96 points. Also, the MPC coil is 97.54% (analysis value) compared to 97.29% (measurement value) for the LCW coil, and the MPC coil and the LCW coil are expected to have approximately the same transmission efficiency.

The embodiment according to one aspect of the present disclosure has been described above. In the first embodiment, by narrowing the gap between the coil conductors at the middle circumference, the lines of magnetic force can be controlled to avoid the coil conductors as much as possible. Furthermore, in the second embodiment, a wall of magnetic material is provided in the coil gap, and the magnetic material is unevenly distributed at the ends of the coils, thereby reducing the bias of the current at the ends. Furthermore, in the second embodiment, the current density flowing in the upper part of the coil is reduced by using a magnetic material in the lower part of the coil so that the magnetic flux attracted to the ferrite passes through the magnetic material. With these ideas, it is possible to realize a wireless transmission coil unit having a transmission efficiency substantially equal to that of a litz wire, although the structure is much simpler than that of a litz wire.

INDUSTRIAL APPLICABILITY The present invention can be used in contactless power feeding systems for electric vehicles, mobile phones, home appliances, medical devices, and other devices with built-in rechargeable batteries.

1 magnetic shield 2 coils 2a, 2c, 2e coil conductors 2b, 2d, 2f gap 3 (3a, 3b, 3c) magnetic material

Claims (3)

A wireless power transmission coil unit comprising a spirally wound planar coil and a magnetic shield provided facing the coil,
The gap between the coil conductor of any winding positioned on the middle circumference of the coil and the coil conductor of the winding adjacent thereto is such that the gap between the coil conductor of any winding positioned on the inner circumference side or the outer circumference side of the coil is is narrower than the gap between the coil conductor of the winding adjacent to the
protruding from the coil on the side opposite to the magnetic shield in the gaps between the coil conductors of arbitrary windings located at least on the inner and outer circumferences of the coil and the coil conductors of windings adjacent thereto a magnetic body is provided, and
A wireless power transmission coil unit , wherein a magnetic body is provided on a part of the surface of the coil opposite to the magnetic shield . 2. The wireless power transmission coil unit according to claim 1 , wherein a magnetic material is provided on the entire surface of the coil facing the magnetic shield. The magnetic material is unevenly distributed on the inner peripheral side of the coil of the arbitrary winding on the inner peripheral portion of the coil, and on the outer peripheral side of the coil of the arbitrary winding on the spiral outer peripheral portion. , The wireless power transmission coil unit according to claim 1 or 2 .

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