transformer

Abstract

To provide a transformer capable of reducing eddy current losses. [Solution] The transformer 1 comprises a core 2 having a central leg portion 21 extending in the vertical direction, side leg portions 22 extending in the vertical direction and provided away from the central leg portion 21 in the left-right direction, and a connecting portion 23 connecting the central leg portion 21 and the side leg portion 22 to each other; a primary winding 3 wound around the central leg portion 21; a secondary winding 4 provided away from the primary winding 3 in the vertical direction and wound around the central leg portion 21; and a pass core 5 that forms a magnetic path for leakage flux together with the core 2, the pass core 5 extending in the left-right direction and provided between the primary winding 3 and the secondary winding 4, wherein the pass core 5 is provided with a gap G2 located between the inner edge 3A of the primary winding 3 in the left-right direction and the outer edge 3B of the primary winding 3 in the left-right direction when viewed from the vertical direction.

Description

Technical Field

[0001] This disclosure relates to a transformer.

Background Art

[0002] A transformer provided with a path core for magnetic flux leakage provided between a primary winding and a secondary winding is known (see, for example, Patent Document 1). In the transformer described in Patent Document 1, the path core protrudes from the central leg portion to the side leg portion of two E-shaped cores facing each other. The E-shaped core has a connecting portion that connects the central leg portion and the side leg portion to each other.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] This disclosure describes a transformer capable of reducing eddy current loss.

Means for Solving the Problems

[0006] A transformer according to one aspect of the present disclosure comprises a core having a central leg extending in a first direction, side legs extending in the first direction and intersecting the first direction and provided away from the central leg in a second direction, and a connecting portion connecting the central leg and the side legs; a primary winding wound around the central leg; a secondary winding provided away from the primary winding in the first direction and wound around the central leg; and a pass core that forms a magnetic path for leakage flux together with the core, the pass core extending in a second direction and provided between the primary winding and the secondary winding. The pass core is provided with a gap located between the inner edge of the primary winding in the second direction and the outer edge of the primary winding in the second direction, as viewed from the first direction.

[0007] For example, if there is no gap in the pass core, the leakage flux passing through the space between the connecting part and the pass core can be distributed over a wide area in the second direction and enter the pass core. In this case, the leakage flux may be tilted with respect to the first direction, and there is a risk of it linking with the primary winding. On the other hand, in the above transformer, the gap provided in the pass core is located between the inner edge and the outer edge of the primary winding when viewed from the first direction. The permeability of the gap is lower than the permeability of the pass core. In other words, a portion with high magnetic resistance is provided in the section of the magnetic path from the central leg through the pass core to the side leg that overlaps with the space between the inner and outer edges of the primary winding when viewed from the first direction. This increases the likelihood that the leakage flux passing through the space between the connecting part and the pass core will not go towards the portion with high magnetic resistance (the gap) but will enter the pass core before reaching the gap. Therefore, the tilt of the leakage flux path with respect to the first direction can be suppressed, and the leakage flux linking with the primary winding can be reduced. As a result, eddy current losses can be reduced.

[0008] The primary winding may be a flatwise coil. In a flatwise coil, a flat rectangular wire, which is composed of a conductive member and an insulating film covering the surface of the conductive member, is wound in a spiral shape. Therefore, a gap exists between the conductive members of the flat rectangular wire in two adjacent turns, extending in the first direction. Some of the leakage flux may pass through this gap. As described above, the flux passing through this gap is also more likely to enter the pass core before reaching the gap, thereby reducing the leakage flux that links with the primary winding. As a result, eddy current losses can be reduced.

[0009] Viewed from the first direction, the gap may coincide with the midpoint of the primary winding where the distance from the inner edge and the distance from the outer edge are equal. When the direction of the voltage applied to the primary winding changes, the direction of the leakage flux passing through the space between the coupling and the pass core changes. Since the gap coincides with the midpoint when viewed from the first direction, the likelihood of both the leakage flux moving from the coupling towards the pass core between the primary winding and the central leg, and the leakage flux moving from the coupling towards the pass core between the primary winding and the side leg, entering the pass core before reaching the gap can be increased, thereby reducing the leakage flux linking with the primary winding. As a result, eddy current losses can be reduced. [Effects of the Invention]

[0010] According to this disclosure, eddy current losses can be reduced. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a perspective view showing a schematic configuration of a transformer according to one embodiment. [Figure 2] Figure 2 is a cross-sectional view along the line II-II in Figure 1. [Figure 3] Figure 3 is a schematic diagram showing the path of leakage flux in the transformer shown in Figure 1. [Figure 4] Figure 4 schematically shows the path of leakage flux in the transformer of the comparative example. [Modes for carrying out the invention]

[0012] A transformer according to one embodiment will be described in detail below with reference to the attached drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and redundant explanations are omitted. Each figure may show an XYZ coordinate system. The Y-axis direction is the direction that intersects (for example, is perpendicular to) the X-axis direction (second direction) and the Z-axis direction (first direction). The Z-axis direction is the direction that intersects (for example, is perpendicular to) the X-axis direction and the Y-axis direction. In the following description, as an example, the X-axis direction will be described as the left-right direction (width direction), the Y-axis direction as the front-back direction (depth direction), and the Z-axis direction as the up-down direction (height direction). The X-axis direction, Y-axis direction, and Z-axis direction are not limited to the directions described above.

[0013] The schematic configuration of a transformer according to one embodiment will be described with reference to Figures 1 and 2. Figure 1 is a perspective view showing the schematic configuration of a transformer according to one embodiment. Figure 2 is a cross-sectional view along the line II-II in Figure 1. The transformer 1 shown in Figures 1 and 2 is a device that converts a primary voltage to a secondary voltage and includes a core 2, a primary winding 3, a secondary winding 4, a pass core 5, and a bobbin 6. Note that the bobbin 6 is not shown in Figure 2.

[0014] Core 2 is a magnetic material that forms a magnetic path. Core 2 includes a central leg 21, a pair of side legs 22, and a pair of connecting parts 23. Each of the central leg 21 and the pair of side legs 22 extends in the vertical direction. The central leg 21 and the pair of side legs 22 are arranged substantially parallel to each other. The pair of side legs 22 are provided apart from the central leg 21 in the left-right direction. In the left-right direction, the central leg 21 is positioned between the pair of side legs 22. The pair of connecting parts 23 are the parts that connect the pair of side legs 22 and the central leg 21 to each other. Each connecting part 23 has a flat plate shape. One connecting part 23 connects one end of the central leg 21 and one end of each side leg 22. The other connecting part 23 connects the other end of the central leg 21 and the other end of each side leg 22.

[0015] In this embodiment, core 2 is an EI core composed of an E-shaped core member 2a and an I-shaped core member 2b, but the shape of core 2 is not limited to this. Core 2 may also be an EE core or a PQ core.

[0016] The primary winding 3 and secondary winding 4 are coil components formed by winding a strip of flat wire in a spiral pattern. The flat wire is composed of a conductive member (e.g., copper) with a rectangular cross-section intersecting (e.g., perpendicular to) its extending direction, and an insulating film covering the surface of the conductive member. The primary winding 3 and secondary winding 4 are flatwise coils formed by winding the flat wire in the thickness direction of the flat wire. The thickness direction of the flat wire is the direction along the short side of the cross-section intersecting (e.g., perpendicular to) the extending direction of the flat wire. The primary winding 3 and secondary winding 4 are wound around the central leg portion 21. The secondary winding 4 is provided away from the primary winding 3 in the vertical direction.

[0017] Each of the primary winding 3 and secondary winding 4 has a predetermined number of turns of flat wire wound around it. In this embodiment, each of the primary winding 3 and secondary winding 4 has 10 turns of flat wire wound around it, but the number of turns of the primary winding 3 and secondary winding 4 can be changed as appropriate.

[0018] In this embodiment, in the left-right direction, the distance from the primary winding 3 to the central leg 21 is substantially equal to the distance from the primary winding 3 to the side leg 22. Similarly, in the left-right direction, the distance from the secondary winding 4 to the central leg 21 is substantially equal to the distance from the secondary winding 4 to the side leg 22. In the left-right direction, the distance from the primary winding 3 to the central leg 21 may be longer or shorter than the distance from the primary winding 3 to the side leg 22. Similarly, in the left-right direction, the distance from the secondary winding 4 to the central leg 21 may be longer or shorter than the distance from the secondary winding 4 to the side leg 22.

[0019] As shown in FIG. 2, the primary winding 3 of the transformer 1 has a plurality of layers laminated in the left-right direction. One layer is composed of a flat wire wound around the central leg portion 21 for one turn. As described above, in the conductive member constituting the primary winding 3, the cross section intersecting the extending direction thereof is rectangular. The outer contour of the cross section is composed of a side linearly extending in one direction and a side linearly extending in a direction orthogonal to the one direction. The primary winding 3 is formed by winding the flat wire in a spiral shape so that one side is parallel to the vertical direction. There is a gap extending in the vertical direction between the conductive members of the flat wire in two adjacent turns. The gap is, for example, an insulating film or an air layer.

[0020] Hereinafter, among the plurality of layers of the primary winding 3, the plurality of layers located inside the gap G2 described later are referred to as inner layers 3a for convenience, and the plurality of layers located outside the gap G2 are referred to as outer layers 3b for convenience. Adjacent inner layers 3a define one gap. Adjacent outer layers 3b define one gap.

[0021] The pass core 5 is a magnetic body that forms a magnetic path MP (see FIG. 3) of leakage magnetic flux together with the core 2. The pass core 5 extends in the left-right direction and is provided between the primary winding 3 and the secondary winding 4 in the vertical direction. The pass core 5 is arranged so that a plurality of gaps are formed between the central leg portion 21 and the side leg portions 22. Note that the gap means a portion where the magnetic body is missing in the magnetic path MP. In the present embodiment, each gap is composed of an air layer or a part of the bobbin 6.

[0022] Specifically, the pass core 5 includes a plurality of divided bodies between the central leg 21 and each side leg 22. The plurality of divided bodies are arranged in the left - right direction while being spaced apart from each other. In this embodiment, the pass core 5 includes two divided bodies (divided bodies 51, 52) between the central leg 21 and each side leg 22. The two divided bodies are arranged in the order of the divided body 51 (the first divided body) and the divided body 52 (the second divided body) from the central leg 21 toward the side leg 22. The divided bodies 51, 52 extend in the left - right direction. The length of the divided body 51 in the left - right direction may be equal to the length of the divided body 52 in the left - right direction.

[0023] A gap G1 is formed between the divided body 51 and the central leg 21. A gap G2 is formed between the divided body 51 and the divided body 52. A gap G3 is formed between the divided body 52 and the side leg 22. In other words, the plurality of gaps formed between the central leg 21 and the side leg 22 include the gap G1, the gap G2, and the gap G3. The gap G1 is the closest to the central leg 21 among the plurality of gaps. The gap G3 is the closest to the side leg 22 among the plurality of gaps. The gap G2 is provided between the gap G1 and the gap G3 in the left - right direction.

[0024] In this embodiment, the length of the gap G1 in the left - right direction (gap length L1) is approximately the same as the length of the gap G3 in the left - right direction (gap length L3). The length of the gap G2 in the left - right direction (gap length L2) is longer than either of the gap lengths L1, L3. The gap lengths L1, L2, and L3 may be approximately the same as each other. The leakage inductance of the transformer 1 is determined according to the sum of the lengths (gap lengths) of the gaps provided on the magnetic path MP along the magnetic path MP. Therefore, the gap lengths of each gap formed between the central leg 21 and the side leg 22 are determined so as to obtain a desired leakage inductance.

[0025] The gap G2 is located between the inner edge 3A of the primary winding 3 in the left-right direction and the outer edge 3B of the primary winding 3 in the left-right direction. In other words, when viewed from the top-bottom direction, the gap G2 is located between the inner edge 3A and the outer edge 3B. More specifically, the inner edge 51a of the segment 51 is located inside the inner edge 3A, and the outer edge 51b of the segment 51 is located outside the inner edge 3A. The inner edge 52a of the segment 52 is located inside the outer edge 3B, and the outer edge 52b of the segment 52 is located outside the outer edge 3B. When viewed from the top-bottom direction, the inner edge 3A overlaps with the segment 51, and the outer edge 3B overlaps with the segment 52. The primary winding 3 includes a midpoint 3C located in the center in the left-right direction. In the left-right direction, the distance from the midpoint 3C to the inner edge 3A is equal to the distance from the midpoint 3C to the outer edge 3B. When viewed from above or below, gap G2 coincides with the midpoint 3C.

[0026] The bobbin 6 is a component that holds the primary winding 3 and the secondary winding 4. The bobbin 6 is made of an insulating material. An example of the insulating material that makes up the bobbin 6 is a resin such as plastic. The bobbin 6 electrically isolates the primary winding 3 and the secondary winding 4, and also electrically isolates the primary winding 3 and the secondary winding 4 from the core 2. The bobbin 6 houses the pass core 5. The bobbin 6 holds each divided part while fixing the position of each divided part. Alternatively, instead of the bobbin 6, the core 2, primary winding 3, secondary winding 4, and pass core 5 may be held by an integral injection mold formed by injection molding, or by potting.

[0027] Next, the effects of transformer 1 will be explained with reference to Figures 3 and 4. Figure 3 is a schematic diagram showing the path of leakage flux in the transformer shown in Figure 1. Figure 4 is a schematic diagram showing the path of leakage flux in a comparative example transformer. For the sake of explanation, the ratio of the dimensions in the X-axis direction to the dimensions in the Z-axis direction in Figures 3 and 4 is different from that in Figure 2. Transformer 100 shown in Figure 4 differs from transformer 1 mainly in that it includes pass core 105 instead of pass core 5.

[0028] The passcore 105 differs from the passcore 5 mainly in that it is not divided into multiple segments. That is, the passcore 105 is composed of a single magnetic material extending in the left-right direction. A gap Gc1 is formed between the inner edge of the passcore 105 and the central leg 21, and a gap Gc2 is formed between the outer edge of the passcore 105 and the side legs 22. The sum of the left-right length of gap Gc1 (gap length Lc1) and the left-right length of gap Gc2 (gap length Lc2) is substantially equal to the sum of the gap lengths L1, L2, and L3 of the transformer 1. The transformer 100 does not have a gap G2, but for convenience, the layer located at the same position as the inner layer 3a of the transformer 1 is referred to as the inner layer 3a, and the layer located at the same position as the outer layer 3b of the transformer 1 is referred to as the outer layer 3b.

[0029] In the transformer 100, magnetic flux is generated when current flows in one direction through the primary winding 3. Of this, a portion of the leakage flux, Φ101, passes through a path (magnetic path) from the central leg 21 of the core 2, through the gap Gc1, the pass core 105, the gap Gc2, the side leg 22, and the connecting part 23, and returns to the central leg 21. When current flows in the reverse direction through the primary winding 3, the leakage flux Φ101 passes through a path from the central leg 21 of the core 2, through the connecting part 23, the side leg 22, the gap Gc2, the pass core 105, and the gap Gc1, and returns to the central leg 21.

[0030] The following explanation describes the case where current flows in one direction through the primary winding 3, and omits the explanation of the case where current flows in the reverse direction through the primary winding 3. Leakage flux may include leakage flux that passes through the space (air layer or bobbin 6) between the connecting part 23 and the pass core 105 without passing through the central leg 21 and the side leg 22. Such leakage flux includes leakage flux Φ102 and leakage flux Φ103. Leakage flux Φ102 passes through a path from the connecting part 23, through the gap between the innermost layer 3a and the central leg 21, the pass core 105, and the gap between the outermost layer 3b and the side leg 22, before returning to the connecting part 23. Leakage flux Φ103 passes through a path from the connecting part 23, through the gap between two adjacent inner layers 3a, the pass core 105, and the gap between two adjacent outer layers 3b, before returning to the connecting part 23.

[0031] In the pass core 105, there is no gap in the section S1 that overlaps with the space between the inner edge 3A and the outer edge 3B when viewed from above, so the permeability in section S1 is constant. That is, the magnetic resistance is constant in section S1. Therefore, the leakage flux Φ102 and leakage flux Φ103 are distributed in the left-right direction and enter the pass core 105. In other words, the leakage fluxes Φ102 and Φ103 can spread over a wide area in the left-right direction. At this time, the closer the position where the leakage fluxes Φ102 and Φ103 enter the pass core 105 is to the side leg portion 22, the more the leakage fluxes Φ102 and Φ103 advance in a way that is inclined with respect to the vertical direction. Therefore, the possibility of the leakage flux Φ102 linking with the primary winding 3 near the lower end of the inner layer 3a increases. Similarly, the likelihood of leakage flux Φ103 linking with the primary winding 3 increases near the lower end of the outer inner layer 3a, which defines the gap through which the leakage flux Φ103 passes. Therefore, eddy current losses may occur.

[0032] In transformer 1, the sum of the gap lengths L1, L2, and L3 is set to be approximately equal to the sum of the gap lengths Lc1 and Lc2 in order to obtain the desired leakage flux. In transformer 1, the leakage flux generated by the flow of current through the primary winding 3 includes leakage flux Φ1, leakage flux Φ2, and leakage flux Φ3.

[0033] In transformer 1, magnetic flux is generated when current flows through the primary winding 3. Of this, a portion of the leakage flux, Φ1, passes through a path (magnetic path) that starts from the central leg 21 of core 2, goes through gap G1, segmented body 51, gap G2, segmented body 52, gap G3, side leg 22, and connecting part 23 in order, and returns to the central leg 21.

[0034] The leakage flux Φ2 travels from the connecting section 23 through the gap between the innermost layer 3a and the central leg 21, the divided body 51, the gap G2, the divided body 52, and the gap between the outermost layer 3b and the side leg 22, before returning to the connecting section 23. The leakage flux Φ3 travels from the connecting section 23 through the gap between two adjacent inner layers 3a, the divided body 51, the gap G2, the divided body 52, and the gap between two adjacent outer layers 3b, before returning to the connecting section 23.

[0035] Here, in transformer 1, the permeability of gap G2 is lower than the permeability of the divided body 51. In other words, in the magnetic path from the central leg 21 through the pass core 5 to the side leg 22, a section with high magnetic resistance is provided in the section that overlaps with the space between the inner edge 3A and the outer edge 3B of the primary winding 3 when viewed from the vertical direction. As a result, the leakage flux Φ2 passing through the space between the connecting section 23 and the pass core 5 is less likely to enter the pass core 5 before reaching gap G2, which is the section with high magnetic resistance. Therefore, the gradient of the path of the leakage flux Φ2 in the vertical direction can be suppressed, and the leakage flux linking with the primary winding 3 can be reduced. As a result, eddy current losses can be reduced.

[0036] Similarly, the leakage flux Φ3 passing through the gap between two adjacent inner layers 3a is more likely to enter the pass core 5 before reaching the gap G2, which is a region with high magnetic resistance. Therefore, the gradient of the path of the leakage flux Φ3 in the vertical direction can be suppressed, and the leakage flux linking with the primary winding 3 can be reduced. As a result, eddy current losses can be reduced.

[0037] Here, in the gap G2, in addition to the magnetic flux traveling in a straight line from the divided body 51 to the divided body 52, there may be a leakage flux Φ4 that passes closer to the primary winding 3 than the gap G2. Such a leakage flux Φ4 is unlikely to occur in the pass core 105, which does not have a gap, but it may occur in the pass core 5, which has a gap G2. When the leakage flux Φ4 links with the primary winding 3, eddy current loss occurs. However, in transformer 1, the leakage flux does not locally link with the primary winding 3 as in transformer 100. Since the magnitude of eddy current loss is proportional to the square of the amount of linked magnetic flux (magnetic flux density), eddy current loss can be reduced compared to transformer 100.

[0038] The primary winding 3 is a flatwise coil. In a flatwise coil, a flat rectangular wire, which is composed of a conductive member and an insulating film covering the surface of the conductive member, is wound in a spiral shape. Therefore, there is a gap extending vertically between the conductive members of the flat rectangular wire in two adjacent turns. Some of the leakage flux Φ3 may pass through this gap. As described above, the leakage flux Φ3 passing through this gap is also more likely to enter the pass core before the gap G2, thereby reducing the leakage flux that links with the primary winding. As a result, eddy current losses can be reduced.

[0039] When viewed from above, the gap G2 coincides with the midpoint 3C of the primary winding 3, where the distance from the inner edge 3A is equal to the distance from the outer edge 3B. When the direction of the voltage applied to the primary winding 3 changes, the direction of the leakage fluxes Φ2 and Φ3 passing through the space between the connecting portion 23 and the pass core 5 changes. Since the gap G2 coincides with the midpoint 3C when viewed from above, the leakage flux Φ2 moving from the connecting portion 23 toward the pass core 5 (divided body 51) between the primary winding 3 and the central leg portion 21, and the leakage flux Φ2 moving from the connecting portion 23 toward the pass core 5 (divided body 52) between the primary winding 3 and the side leg portion 22, can both increase the possibility of entering the pass core 5 before reaching the gap G2, thereby reducing the leakage flux linked with the primary winding 3. The leakage flux Φ3 traveling from the connecting portion 23 toward the pass core 5 (divided body 51) in the gap between two adjacent inner layers 3a, and the leakage flux Φ3 traveling from the connecting portion 23 toward the pass core 5 (divided body 52) in the gap between two adjacent outer layers 3b, can both increase the likelihood of entering the pass core 5 before reaching the gap G2, thereby reducing the leakage flux linked with the primary winding 3. As a result, eddy current losses can be reduced.

[0040] In the divided body 52, leakage flux Φ2 and Φ3 may be generated, leaking from the divided body 52 toward the primary winding 3. This leakage flux includes a vertical component. As described above, a leakage flux Φ4 is generated in the gap G2 and enters the divided body 52 in the vicinity of the gap G2. At this time, the leakage flux Φ4 may intersect and cancel out a portion of the leakage flux leaking from the divided body 52 toward the primary winding 3. More specifically, the leakage flux Φ4 intersects and cancels out a portion of the leakage flux leaking from the divided body 52 in the region of the divided body 52 closest to the gap G2. As an example, the leakage flux Φ4 generated from the leakage flux Φ2 and passing closer to the primary winding 3 than the gap G2 intersects with the leakage flux Φ3 and cancels out with the leakage flux Φ3. As a result, the amount of flux linked to the primary winding 3 decreases. Consequently, it becomes possible to reduce eddy current losses.

[0041] Although embodiments of the present disclosure have been described in detail above, the transformers relating to the present disclosure are not limited to the embodiments described above.

[0042] The primary winding 3 and secondary winding 4 may be edgewise coils. That is, the primary winding 3 and secondary winding 4 may be constructed by spirally winding a long conductive member. The primary winding 3 and secondary winding 4 may also be coil components constructed by winding them in an α-winding pattern around the central leg portion 21.

[0043] When viewed from above, the gap G2 does not necessarily have to overlap with the midpoint 3C. For example, when viewed from above, the gap G2 may be located between the inner edge 3A and the midpoint 3C, or between the outer edge 3B and the midpoint 3C.

[0044] The Passoa 5 may have three or more divisions. In this case, at least one gap formed between two adjacent divisions is located between the inner edge 3A and the outer edge 3B in the left-right direction. Another gap may be located between the inner edge 3A and the outer edge 3B, or it may be located inside the inner edge 3A, or it may be located outside the outer edge 3B. [Explanation of symbols]

[0045] 1...Transformer, 2...Core, 3...Primary winding, 3A...Inner edge, 3B...Outer edge, 3C...Midpoint, 4...Secondary winding, 5...Pass core, 21...Central leg, 22...Side leg, 23...Connecting part, 51...Split body (first split body), 52...Split body (second split body), G2...Gap.

Claims

1. A core having a central leg portion extending in a first direction, a side leg portion extending in the first direction and intersecting the first direction and provided away from the central leg portion in a second direction, and a connecting portion connecting the central leg portion and the side leg portion to each other, The primary winding wrapped around the central leg portion, A secondary winding is provided in the first direction, away from the primary winding, and wound around the central leg, A pass core that forms a magnetic path for leakage flux together with the core, the pass core extending in the second direction and provided between the primary winding and the secondary winding, Equipped with, A transformer wherein the pass core is provided with a gap located between the inner edge of the primary winding in the second direction and the outer edge of the primary winding in the second direction, as viewed from the first direction.

2. The transformer according to claim 1, wherein the primary winding is a flatwise coil.

3. The transformer according to claim 1 or 2, wherein, viewed from the first direction, the gap coincides with the midpoint of the primary winding, where the distance from the inner edge is equal to the distance from the outer edge.

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