transformer

Abstract

A transformer capable of reducing both fringing loss and loss caused by interlinked magnetic flux in the plane direction of a winding. [Solution] The transformer 1 comprises an annular core 10 formed by connecting a plurality of cores 10a and 10b made of a magnetic material in a ring shape with a plurality of gaps 11a and 11b interposed therebetween, primary windings 21a and 21b for excitation wound around the annular core, and secondary windings 22a and 22b, the secondary windings 22a and 22b being wound around the annular core 10 at positions sandwiched between the plurality of gaps.

Description

[Technical Field]

[0001] The present invention relates to a transformer. [Background technology]

[0002] In recent years, power conversion devices have become smaller and lighter, leading to higher frequencies and more high-frequency currents flowing through transformers. There has also been an increase in conversion devices in which the fundamental wave component becomes the carrier frequency, such as the high-frequency transformer current of LLC resonant converters and Dual Active Bridge (DAB) converters. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-107178

[0004] [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-186405 Summary of the Invention [Problem to be solved by the invention]

[0005] As shown in FIG. 8, in a transformer, gaps 301a and 301b are provided midway through core 201 to adjust inductance. When gaps are provided in this manner, the magnetic flux expands at the gap, causing a fringing phenomenon in which the magnetic flux passes through a cross-sectional area larger than the cross-sectional area of ​​the core. This expanded magnetic flux is called fringing flux. FIG. 8 illustrates fringing flux 321a. Fringing flux 321a interlinks with core 201 and winding 311, generating eddy currents and increasing loss. Loss due to fringing flux is called fringing loss, and the longer the gap length, the greater the fringing flux and the greater the loss. Furthermore, the higher the frequency, the greater the eddy currents generated, resulting in greater loss.

[0006] One method for reducing fringing loss caused by fringing magnetic flux linking the core is to change the core shape to reduce the magnetic flux components that link perpendicularly to the core (see, for example, Patent Document 1). However, this makes the core shape more complex and increases manufacturing costs.

[0007] Furthermore, increasing the distance between the core and the winding is an effective method for reducing fringing loss caused by linkage with the winding (for example, Patent Document 2). In Patent Document 2, as shown in Fig. 8, fringing loss of the winding is reduced by providing a large gap 301b in a location where no winding is wound. However, with this structure, fringing magnetic flux links with the core, so fringing loss of the core cannot be reduced.

[0008] Furthermore, neither Patent Document 1 nor Patent Document 2 is able to reduce eddy current loss, which occurs when part of the magnetic flux generated by the winding interlinks with the plane of the winding, as shown in FIG. 9. FIG. 9 shows a transformer similar to that shown in FIG. 8, along with an XYZ orthogonal coordinate system consisting of mutually orthogonal X-, Y-, and Z-axes. FIG. 9 also shows magnetic flux 341 generated by current 331 in winding 311a. This magnetic flux 341 interlinks with the plane of winding 311a, i.e., the yz plane in FIG. 9, causing eddy current loss in winding 311a.

[0009] The present invention has been made in consideration of the above-described circumstances, and has as its object to provide a transformer that can reduce both fringing loss and loss caused by in-plane interlinkage magnetic flux of the windings. [Means for solving the problem]

[0010] A transformer according to one aspect of the present invention comprises an annular core formed by connecting a plurality of cores made of a magnetic material in a ring shape with a plurality of gaps interposed therebetween, a primary winding for excitation wound around the annular core, and a secondary winding, the secondary winding being wound around the annular core at a position sandwiched between the plurality of gaps.

[0011] In another preferred embodiment, an insulating material is sandwiched between the plurality of cores and the secondary winding.

[0012] In another preferred embodiment, the secondary winding is made of a plurality of rectangular wires.

[0013] Another preferred aspect is characterized in that the fringing magnetic flux Φa2 generated in the plurality of gaps and the magnetic flux Φw interlinked in the plane direction of the winding generated by the current flowing in the secondary winding satisfy the following formula: Φa2<2Φw [Effects of the Invention]

[0014] According to this invention, the fringing magnetic flux can be canceled out by the in-plane magnetic flux of the winding other than the excitation winding of the transformer, thereby suppressing both the fringing loss of the core and the loss caused by the in-plane interlinkage magnetic flux of the winding. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a front view of a transformer according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing an example of a winding in the transformer. [Figure 3] FIG. 2 is a front view showing magnetic flux generated in the transformer. [Figure 4] FIG. 2 is a perspective view showing magnetic flux generated in the transformer. [Figure 5] FIG. 4 is a front view of a transformer according to a second embodiment of the present invention. [Figure 6] FIG. 2 is a front view showing magnetic flux generated in the transformer. [Figure 7] FIG. 4 is a front view of a transformer according to a second embodiment of the present invention. [Figure 8] FIG. 1 is a front view showing an example of a conventional transformer. [Figure 9] FIG. 2 is a front view showing magnetic flux generated in the transformer. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] <Common Features of Each Embodiment> The embodiments of the present invention share a common feature: in the transformers according to the embodiments of the present invention, a gap is provided at a position where the in-plane interlinkage magnetic flux of the winding and the magnetic flux flowing in the core are in the same direction (for example, the x-axis direction in FIG. 1), and the winding that is not the excitation winding of the transformer (for example, the secondary winding when the primary winding is the excitation winding) is arranged below the gap.

[0018] With this configuration, the fringing magnetic flux can be canceled out by the in-plane magnetic flux of the winding that is not the excitation winding of the transformer, thereby suppressing both the fringing loss of the core and the loss caused by the in-plane interlinkage magnetic flux of the winding.

[0019] First Embodiment Figure 1 is a front view of a transformer 1 according to a first embodiment of the present invention. The transformer 1 is shown in Figure 1 along with an XYZ Cartesian coordinate system. As shown in Figure 1, the transformer 1 includes an annular core 10 formed by connecting multiple cores made of a magnetic material in an annular shape with multiple gaps between them, a primary winding 21 for excitation wound around the annular core 10, and a secondary winding 22 not for excitation.

[0020] In the illustrated example, annular core 10 is made up of cores 10a and 10b and gaps 11a and 11b. Primary winding 21 is made up of primary windings 21a and 21b, and secondary winding 22 is made up of secondary windings 22a and 22b. Primary winding 21a and secondary winding 22a are wound around core 10a, and primary winding 21b and secondary winding 22b are wound around core 10b. Gaps 11a and 11b are provided between cores 10a and 10b. The secondary winding is wound around annular core 10 at a position sandwiched between the gaps. Specifically, in FIG. 1, secondary windings 22a and 22b are arranged below gap 11a and above gap 11b, respectively.

[0021] In Fig. 1, primary winding 21 and secondary winding 22 have a rectangular cross-sectional shape with width w longer than thickness t. In Fig. 1, width w is in the Y-axis direction, and thickness t is in the X-axis direction. Note that primary winding 21 and secondary winding 22 may be formed from a divided rectangular wire, as shown in Fig. 2, or may be formed from a winding with N turns (N is plural). Furthermore, primary windings 21a and 21b and secondary windings 22a and 22b may be connected in series or in parallel.

[0022] Fig. 3 shows the magnetic flux generated in the transformer 1 along with an XYZ Cartesian coordinate system. In Fig. 3, the primary windings 21a and 21b are excitation windings, and the direction of magnetic fluxes 51a and 51b generated by currents flowing through the primary windings 21a and 21b is the same as the direction of the magnetic flux flowing through the cores 10a and 10b (fringing magnetic flux).

[0023] On the other hand, the direction of magnetic flux Φw generated by the current flowing through secondary windings 22a and 22b is opposite to the direction of magnetic flux (including fringing magnetic flux) flowing through annular core 10. Therefore, in Fig. 3, when considering magnetic flux in the x-axis direction, the fringing magnetic flux and magnetic flux Φw generated by secondary windings 22a and 22b cancel each other out. Therefore, the fringing magnetic flux linking to annular core 10 and the magnetic flux linking in the surface direction (xz plane) of primary windings 21a and 21b are reduced, thereby suppressing the resulting fringing loss of annular core 10 and eddy current loss in the windings.

[0024] Figure 4 shows fringing flux and the magnetic flux generated by the current flowing through the secondary windings. Figure 4 also shows fringing flux Φa1, Φa2, Φb1, and Φb2 generated between cores 10a and 10b, and magnetic flux Φw generated by the current through secondary windings 22a and 22b. The suppression effect of fringing loss in cores 10a and 10b and eddy current loss generated by the current through secondary windings 22a and 22b is maximized when the x-component Φw of the magnetic flux generated in secondary windings 22a and 22b is equal to the fringing flux Φa2 expanding toward secondary windings 22a and 22b. Furthermore, when fringing flux Φa2 is smaller than the x-component Φw of the magnetic flux generated in secondary windings 22a and 22b, fringing loss in cores 10a and 10b does not occur, reducing eddy current loss in the windings, thereby enabling loss suppression with this structure. On the other hand, if the fringing magnetic flux Φa2 is larger than the x-component Φw of the magnetic flux generated in the secondary winding 22, the fringing loss of the core is reduced, but eddy current loss in the windings may increase. Therefore, when the fringing magnetic flux Φa2 is larger than the x-component Φw of the magnetic flux generated by the secondary windings 22a and 22b, at least the following equation must be true: Φa2<2Φw ……(1)

[0025] Therefore, in this embodiment, the effect of suppressing fringing loss of the annular core 10 and eddy current loss due to the current in the windings is achieved when the above formula (1) holds between the x-component Φw of the magnetic flux generated by the secondary windings 22a and 22b and the fringing magnetic flux Φa2 expanding toward the secondary windings 22a and 22b.

[0026] Therefore, in this embodiment, the magnetic flux Φa2 is adjusted by adjusting the magnetic permeability of the core material, and the magnetic flux Φw is adjusted by adjusting the number of turns of the secondary windings 22a and 22b, thereby satisfying the above formula (1).

[0027] According to this embodiment, it is possible to reduce both fringing loss and loss caused by in-plane interlinkage magnetic flux of the winding.

[0028] Second Embodiment In the first embodiment described above, gaps 11a and 11b are provided in the center of the top and bottom of the annular core 10, but the position of gap 11 does not have to be in the center of the top and bottom of the annular core 10 as long as it is above or below a winding that is not an excitation winding, and the number of gaps 11 does not have to be two.

[0029] FIG. 5 is a front view of a transformer 1A according to a second embodiment of the present invention. In this embodiment, gap 11 is not located in the center between the top and bottom of annular core 10A, and there are four gaps. In this embodiment, a primary winding 21a and a secondary winding 22a are wound around core 10a, and a primary winding 21b and a secondary winding 22b are wound around core 10b. Gap 11a is provided between cores 10a and 10c, gap 11b is provided between cores 10c and 10b, gap 11c is provided between cores 10a and 10d, and gap 11d is provided between cores 10b and 10d. Secondary winding 22a is located below gap 11a and above gap 11c, and secondary winding 22b is located below gap 11b and above gap 11d.

[0030] FIG. 6 shows the magnetic flux generated in transformer 1A along an XYZ Cartesian coordinate system. Primary windings 21a and 21b are excitation windings, while secondary windings 22a and 22b are not. The direction of magnetic flux 51 generated by the current flowing through primary windings 21a and 21b is the same as the direction of magnetic flux flowing through annular core 10A (fringing magnetic flux). Meanwhile, the direction of magnetic flux Φwa and Φwb generated by the current flowing through secondary windings 22a and 22b is opposite to the direction of magnetic flux flowing through annular core 10A (fringing magnetic flux). Therefore, considering the magnetic flux in the x-axis direction, the fringing magnetic flux and the magnetic flux generated by secondary winding 22 cancel each other out. This reduces the fringing magnetic flux linking the core and the magnetic flux linking in the plane direction of the windings (xz plane), thereby suppressing the resulting fringing loss of the core and eddy current loss in the windings.

[0031] Third Embodiment In the first and second embodiments, a gap is provided between the annular cores 10 and 10A and the secondary windings 22a and 22b, but an insulating material 30 may be sandwiched between them to ensure an insulating distance.

[0032] 7 is a front view of a transformer 1B according to a third embodiment of the present invention. This transformer 1B is configured such that insulating materials 30a and 30b are sandwiched between the annular core 10 and the secondary windings 22a and 22b of the transformer 1 according to the first embodiment.

[0033] This embodiment also provides the same effects as those of the first embodiment. Furthermore, according to this embodiment, the insulation distance between the annular core 10 and the secondary windings 22a and 22b can be increased.

[0034] <Other embodiments> Although the first to third embodiments of the present invention have been described above, the present invention may have other embodiments, such as the following.

[0035] (1) In the third embodiment, an insulating material is sandwiched between the multiple cores and the secondary winding in the first embodiment, but an insulating material may be sandwiched between the multiple cores and the secondary winding in the second embodiment.

[0036] (2) In the second or third embodiment, the above formula (1) may be established.

[0037] (3) The primary winding and the secondary winding may be wound on only one side of the two annular cores. For example, in the first embodiment (FIG. 1), the primary winding 21b and the secondary winding 22b wound on the annular core 10b may be omitted. [Explanation of symbols]

[0038] 1, 1A, 1B...transformer, 10, 10A...annular core, 10a, 10b, 10c, 201...core, 11, 11a, 11b, 11c, 11d...gap, 21, 21a, 21b...primary winding, 22, 22a, 22b...secondary winding, 30, 30a...insulation material, 341, Φw, Φwa...magnetic flux, 321a, Φa2...fringing flux, 331...current.

Claims

1. an annular core formed by connecting a plurality of cores made of a magnetic material in an annular shape with a plurality of gaps therebetween; a primary winding for excitation and a secondary winding wound around the annular core; the secondary winding is wound around the annular core at a position sandwiched between the plurality of gaps; A transformer characterized by:

2. an insulating material is sandwiched between the plurality of cores and the secondary winding. The transformer according to claim 1 .

3. The secondary winding is made of a plurality of rectangular wires. The transformer according to claim 1 .

4. The fringing magnetic flux Φa2 generated in the plurality of gaps and the magnetic flux Φw interlinked in the plane direction of the winding generated by the current flowing in the secondary winding satisfy the following formula: The transformer according to claim 1 . Φa2<2Φw

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