JP2019160985A - Transformer and llc resonance circuit using the same - Google Patents

Abstract

To provide a transformer in which leakage flux interlinking with winding is reduced significantly.SOLUTION: A transformer 1 includes a core body forming a first closed magnetic circuit 81 by multiple legs and a coupling part for coupling between the legs, and a coil body attached to the leg of the core body. The coil body includes a primary winding 21 and a secondary winding 22 placed around the leg while being separated from each other in the radial direction, and an additional core 5 sandwiched between the primary winding 21 and the secondary winding 22 entirely in the hoop direction, and forming second closed magnetic circuits 82a, 82b in combination with the leg and the coupling part.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an insulating transformer and an LLC resonant circuit using the transformer.

  In the LLC resonance circuit, a technique for performing a resonance operation using a leakage inductance obtained by mounting the primary winding and the secondary winding of the transformer apart from each other is known. For example, in Patent Document 1, a primary winding and a secondary winding are wound at a distance in the longitudinal direction of the bobbin (a direction perpendicular to the winding direction of the winding), and the bobbin is wound around the middle leg portion of the core. A technique for insertion is disclosed.

  Patent Document 2 discloses a technique related to an electric wire that can reduce eddy currents caused by an external magnetic field that has entered the inside and can suppress loss due to a proximity effect.

JP-A-2005-33938 International Publication No. 2013/42671

  However, when mounting as in Patent Document 1, leakage magnetic flux is interlinked with the winding of the transformer, eddy current loss is induced in the winding, and the temperature of the winding rises (Patent Document 2). reference). In recent years, there has been a demand for a transformer that operates at a high input voltage and a high frequency.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a transformer in which the leakage magnetic flux interlinking with the winding is remarkably reduced.

  The transformer according to the first aspect of the present invention includes a core having a plurality of leg portions and a connecting portion connecting the plurality of leg portions, and forming a first closed magnetic circuit by the plurality of leg portions and the connecting portion. A main body, and a coil main body mounted on the leg portion of the core main body, wherein the coil main body is separated from each other in a radial direction, and a primary winding and a secondary coil disposed around the leg portion. A winding, and an additional core sandwiched between the primary winding and the secondary winding over the entire circumferential direction and combined with the leg portion and the connecting portion to form a second closed magnetic circuit. It is characterized by that.

  According to this aspect, by inserting an additional core between the primary winding and the secondary winding, a magnetic flux is passed between both windings to form a second closed magnetic circuit for obtaining a necessary leakage inductance. is doing. The magnetic flux passing through the second closed magnetic path does not interlink with the primary winding and the secondary winding. That is, the amount of magnetic flux linked to the primary winding and the secondary winding can be significantly reduced as compared with the prior art that actively uses the leakage inductance of the transformer. Thereby, the eddy current induced in the primary winding and the secondary winding is greatly reduced, and the rise in winding temperature can be remarkably reduced.

  According to the present invention, the leakage magnetic flux interlinked with the winding can be remarkably reduced, so that it is possible to prevent the transformer from generating excessive heat.

It is the perspective view which looked at the transformer concerning this embodiment from the slanting upper side. It is the disassembled perspective view which looked at the core from diagonally upper side. It is the disassembled perspective view which looked at the trans | transformer from diagonally upper side. It is the IV-IV sectional view taken on the line of FIG. It is the perspective view which looked at the additional core from diagonally upper side. It is a figure which shows the structural example of the LLC resonant circuit which concerns on this embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or its application.

  The transformer according to the present embodiment and the LLC resonant circuit using the transformer are, for example, a power conditioner that converts the generated power of the photovoltaic power generation apparatus and is connected to a commercial power supply system or supplied to a load. used.

  In the transformer according to the present disclosure, an additional core is sandwiched between the primary winding and the secondary winding, and a second closed magnetic circuit that allows the magnetic flux to pass between the two windings is formed. There is a feature in the point that I got.

  Hereinafter, a specific description will be given with reference to the drawings.

-Transformer configuration-
As shown in FIG. 1, the transformer 1 includes a core 4 as a core body and a coil body 2 attached to the core 4.

  As shown in FIG. 2, the core 4 has a pair of upper and lower core parts (hereinafter referred to as an upper core part 4a and a lower core part 4b). The upper core portion 4a and the lower core portion 4b are symmetrical with respect to a virtual plane formed at the center position (joining position) in the vertical direction as viewed from the front of the drawing. That is, the upper core portion 4a and the lower core portion 4b are common members having the same shape, and are used by being turned upside down. And the upper core part 4a and the lower core part 4b are joined in the state which faced | matched the end surfaces of the open side of both the core parts 4a and 4b, ie, the end surfaces of the middle leg part 42 and the outer leg part 43, mutually. Yes.

  In the following description, only the configuration of the lower core portion 4b will be described, and the description of the configuration of the upper core portion 4a will be omitted. In the following description, the axial direction (standing direction) of the leg portion of the core 4 is referred to as the up-down direction. 1 to 4, the vertical direction of the core 4 is illustrated so as to be the vertical direction in the drawings, and “upper” and “lower” are defined according to the drawings for convenience of explanation.

  The lower core portion 4 b includes a substantially rectangular plate-like base body 41 extending in the left-right direction orthogonal to the up-down direction, a middle leg portion 42 erected upward on the base body 41, and a pair of outer leg portions 43. A portion of the base body 41 that connects the middle leg portion 42 and the outer leg portion 43 corresponds to a connecting portion.

  The middle leg portion 42 has a cylindrical shape, and is integrally provided at an intermediate position in the left-right direction of the base body 41. Further, the cross-sectional shape of the middle leg portion 42 is slightly smaller than the opening of the insertion hole 34 of the bobbin 3 described later, and a part or all of the middle leg portion 42 can be accommodated in the bobbin main body 32 of the bobbin 3 described later. Has been.

  The outer leg portion 43 is erected on both sides of the middle leg portion 42 in the left-right direction. The distance between the middle leg portion 42 and the outer leg portion 43 is set slightly wider than the radial thickness of the coil body 40 so that the coil body 2 can be attached to the middle leg portion 42. Further, in both outer leg portions 43, the inner wall in the facing direction facing the other outer leg portion 43 is cut out on an arc according to the shape of the coil body 2.

  Further, as shown in FIG. 4, the length of the middle leg portion 42 is shorter than that of the outer leg portion 43 to form a gap Gm between the middle leg portions 42 of the upper and lower cores. However, the position of the gap Gm is not particularly limited, and may be another position (for example, the end of the middle leg portion 42 in the vertical direction). Further, the gap Gm may be provided at a plurality of locations, and the same effect as the configuration of FIG. 4 can be obtained.

  As shown in FIGS. 3 and 4, the coil body 2 includes a bobbin 3 and primary windings 21 and 2 arranged around the middle leg portion 42 in a state of being separated from each other in the radial direction with respect to the bobbin 3. A secondary winding 22 and an additional core 5 sandwiched between the primary winding 21 and the secondary winding 22 are provided. In order to facilitate understanding of the description, in FIG. 3, the additional core 5 is hatched. Similarly, in FIG. 4, the primary winding 21 is hatched with a right-upward diagonal line, and the secondary winding 22 is hatched with a left-upward diagonal line.

  In the bobbin 3, two discs 31 each having a circular through-hole formed in the center are arranged to face each other, and the discs 31 are connected by a cylindrical bobbin main body 32. As a result, the bobbin 3 is formed with an insertion hole 34 for inserting the middle leg portion 42 of the core 4.

  The primary winding 21 and the secondary winding 22 are arranged around the middle leg portion 42 in a state of being separated from each other in the radial direction with respect to the bobbin main body 32. In other words, the primary winding 21 and the secondary winding 22 are concentrically wound around the bobbin main body 32, respectively, and are arranged so as to be separated on the inner side and the outer side in the radial direction.

  FIG. 3 shows an example in which the primary winding 21 is wound on the inner peripheral side and the secondary winding 22 is wound on the outer peripheral side. More specifically, the primary winding 21 is wound to form a plurality of layers on the outside of the bohin body 32, and the additional core 5 is wound so as to cover the outside of the primary winding 21, The secondary winding 22 is wound so as to form a plurality of layers on the outside.

  FIG. 3 shows an example in which the primary winding 21 has a three-layer structure and the secondary winding 22 has a two-layer structure, but the number of turns of both the windings 21 and 22 depends on the required characteristics. It can be set arbitrarily. In FIG. 3, the primary winding 21 is wound around the bobbin 3 on the inner peripheral side and the secondary winding 22 is wound around the outer peripheral side, but the present invention is not limited to this. For example, with respect to the bobbin 3, the secondary winding 22 may be wound on the inner peripheral side, and the primary winding 21 may be wound on the outer peripheral side.

  In general, in order to increase the coupling coefficient k indicating the degree of coupling between the two windings 21 and 22, it is better that the distance between the primary winding 21 and the secondary winding 22 is short. Therefore, by performing the winding method as in the present embodiment, the coupling coefficient is compared with the case where the primary winding and the secondary winding are wound apart in the longitudinal direction of the bobbin as in Patent Document 1. k can be increased. Thereby, since the magnetic flux linked with the primary winding 21 and the secondary winding 22 can be made small, the effect which suppresses the heat_generation | fever of the transformer 1 (coil main body 2) is acquired.

  In addition, the material and wire diameter of the strands of the primary winding 21 and the secondary winding 22 are not particularly limited. For example, the primary winding 21 and the secondary winding 22 are made of copper, for example, and are litz wires having a strand diameter of 0.03 to 0.1 mmφ.

  When the coupling coefficient k between the primary winding 21 and the secondary winding 22 is high, the leakage inductance Lr resulting from the mutual relationship between the primary winding 21 and the secondary winding 22 is reduced accordingly. Therefore, in this embodiment, in addition to the first closed magnetic path 81 formed by the middle leg portion 42, the base body 41, and the outer leg portion 43, the magnetic flux passes between the primary winding 21 and the secondary winding 22. The second closed magnetic circuit 82 is formed, and the leakage inductance Lr is obtained therefrom.

  Hereinafter, the configuration of the additional core 5 and the formation of the closed magnetic paths 81 and 82 (generation of the leakage inductance Lr) will be described in more detail.

  As shown in FIGS. 3 and 4, the additional core 5 is sandwiched between the primary winding 21 and the secondary winding 22 over the entire circumferential direction, and part or all of the additional core 5 is formed of a magnetic material. Yes.

  For example, as shown in FIG. 5, the additional core 5 is a sheet-like body, a rectangular core portion 51 formed of a magnetic material, and a rectangular heat conduction having a higher thermal conductivity than the core portion 51. The parts 52 are alternately arranged in the longitudinal direction of the additional core 5. In FIG. 5, the core portion 51 is hatched for easy understanding of the description.

  A rectangular thin plate made of a magnetic material can be applied to the core portion 51. The material of the core part 51 is not specifically limited. For example, the core part 51 may be formed of a material common to the core 4 or another magnetic material may be used.

  For example, a rectangular thin plate made of silicon can be applied to the heat conducting unit 52. Thus, by providing the heat conducting portion 52, the heat conducting performance of the transformer 1 can be enhanced.

  FIG. 5 shows an example in which the size of the core portion 51 and the size of the heat conducting portion 52 are the same. That is, the width D51 of the core portion 51 and the width D52 of the heat conducting portion 52 are equal to each other, and the lengths L thereof are aligned.

  However, the configuration of FIG. 5 is merely an example and is not limited thereto. For example, the width of the core portion 51 in the sheet longitudinal direction (hereinafter simply referred to as the width) and the width of the heat conducting portion can be arbitrarily set. For example, the width of each of the core part 51 and the heat conduction part 52 can be set according to necessary heat conduction performance and magnetic performance. Further, the heat conducting portion 52 may be omitted, and all of the additional cores 5 may be configured by the core portion 51 made of a magnetic material.

  As described above, by providing the additional core 5 between the primary winding 21 and the secondary winding 22, the primary winding 21 and the secondary winding as shown by phantom lines in FIG. A second closed magnetic path 82 for allowing magnetic flux to pass between the windings 22 can be formed. Here, the second closed magnetic path 82 includes a closed magnetic path 82a formed by the additional core 5, the base body 41, and the outer leg portion 43, and a closed magnetic path 82b formed by the additional core 5, the base body 41, and the middle leg portion 42. Including.

-Configuration of LLC resonant circuit-
As shown in FIG. 6, the LLC resonance circuit A receives a power supply voltage Vi from a power supply E at an input terminal IN, converts it into alternating current and outputs it, and outputs the resonance part 60 to a predetermined output voltage Vo. And a control circuit 7 including a conversion unit 62 that converts the signal into an output terminal OUT and outputs the output from the output terminal OUT. In the following description, when the input terminal IN is described separately on the positive electrode side and the negative electrode side, it may be described with reference numerals INP and INM. Similarly, when the output terminal OUT is described separately on the positive electrode side and the negative electrode side, it may be described with OUTP and OUTM, respectively.

  The resonance unit 60 includes a switching unit 61, resonance capacitors C11 and C12, and the transformer 1 described above.

  The switching unit 61 includes first and second switching elements Q11 and Q12 provided in series between a positive input terminal INP and a negative input terminal INM. FIG. 6 shows an example in which N-type MOS-FETs and parasitic diodes are connected in parallel as the first and second switching elements Q11 and Q12. The configuration of the switching unit 61 is not limited to the configuration of FIG. 6, and other switching circuits having the same function may be applied.

  The resonance capacitors C11 and C12 include a current resonance capacitor C11 and a voltage resonance capacitor C12. The voltage resonance capacitor C12 is connected in parallel to the first switching element Q11. Similarly, a series circuit of the current resonance capacitor C11 and the primary winding 21 of the transformer 1 is connected in parallel to the first switching element Q11.

  In other words, the positive-side input terminal INP is connected to one end (for example, the winding start end) of the primary winding 21 of the transformer 1 via the first resonance capacitor C11. The other end (for example, the winding end) of the primary winding 21 of the transformer 1 is connected to the negative-side input terminal INM via the second switching element Q12. The first switching element Q11, the first resonance capacitor C11, and the primary winding 21 of the transformer 1 form a closed loop circuit.

  The conversion unit 62 is a circuit that converts the resonance voltage output from the resonance unit 60 into a predetermined output voltage Vo and outputs the converted voltage. Specifically, the converter 62 includes a second capacitor C21 and a diode D22 connected in series between one end (for example, the winding start end) of the secondary winding 22 of the transformer 1 and the positive output terminal OUTP. The diode D22 is connected in the forward direction from one end of the secondary winding 22 of the transformer TR1 toward the positive output terminal OUTP. The other end (for example, the winding end) of the secondary winding 22 of the transformer 1 is connected to the negative output terminal OUTM.

  The converter 62 further includes a backflow prevention diode D2 connected in series between the intermediate node N62 between the second capacitor C21 and the diode D22 and the negative output terminal OUTM. The backflow prevention diode D21 is connected in a direction opposite to the direction from the intermediate node N62 toward the negative output terminal OUTM. An output capacitor C22 is connected between the output terminals OUT.

  The control circuit 7 controls the operation of the entire LLC resonance circuit A, and can be realized by, for example, an IC (Integrated Circuit). The control circuit 7 operates, for example, according to a program or sequence registered in advance in its own circuit. More specifically, the control circuit 7 outputs, for example, control signals Vg11 and Vg12 for on / off control of the first and second switching elements Q11 and 12 of the switching unit 7, respectively.

  In the present disclosure, the term “connection” includes all electrical connections. In other words, the “connection” is not limited to a direct connection, but includes a concept including an electrical connection via, for example, a resistance element or a semiconductor element.

  The inventor has 1 of an LLC resonance circuit A (hereinafter referred to as an implementation circuit A) to which the transformer 1 according to the present embodiment is applied and an LLC resonance circuit (hereinafter referred to as a comparison circuit) according to a configuration in which an attached coil is not provided. A comparative test of the degree of increase in the next winding temperature was conducted. Although a specific illustration is omitted, the comparison circuit uses a PQ-type core, and the leakage inductance is reduced by shifting the winding positions of the primary winding and the secondary winding of the coil body in the axial direction. Is generated. Otherwise, the implementation circuit A and the comparison circuit have a common configuration.

  In the measurement method, both the implementation circuit A and the comparison circuit apply 270 V and 330 V as the power supply voltage Vi, and measure the temperature change of the primary winding 21 of the transformer 1 using a thermocouple after a predetermined time has elapsed. did.

  As a result, in the comparison circuit, when the power supply voltage Vi was increased from 270 V to 330 V, the temperature increased by about 21 degrees, whereas in the implementation circuit A, the temperature increased by about 10 degrees and the temperature increase range. It was confirmed that the temperature rise was substantially halved and the temperature rise was greatly reduced.

  Furthermore, the inventor measured the leakage magnetic flux of the implementation circuit A and the comparison circuit. As a method for measuring the leakage magnetic flux, a measuring coil was brought close to the transformer while the transformer 1 was energized, and the induced voltage induced in the measuring coil was measured.

  As a result, in the implementation circuit, the induced voltage was ¼ or less than that of the comparison circuit, and it was confirmed that the leakage flux to the outside of the transformer 1 was significantly reduced in the implementation circuit.

  As described above, according to the present embodiment, the additional core 5 is provided between the primary winding 21 and the secondary winding 22 of the transformer 1, and the second closed magnetism allows the magnetic flux to pass between both the windings 21 and 22. A path 82 is formed. Thereby, for example, a desired leakage inductance Lr necessary for the resonance operation can be obtained. Further, the magnetic flux passing through the second closed magnetic path 82 does not interlink with the primary winding 21 and the secondary winding 22 (element wire) of the coil body 2. That is, the amount of magnetic flux interlinked with the primary winding 21 and the secondary winding 22 of the transformer 1 is compared with the case where the resonance operation is positively performed using the leakage inductance of the transformer as in the prior art. It can be significantly reduced. In the prior art, the leakage flux interlinks with the winding of the transformer, leading to eddy current loss in the winding and increasing the winding temperature. However, in the configuration of this embodiment, the leakage flux is wound. Since the leakage inductance Lr can be obtained without interlinking the wires, such a temperature rise can be remarkably reduced.

<Other embodiments>
The preferred embodiments of the present invention and the modifications thereof have been described above, but the technology according to the present disclosure is not limited thereto, and can be applied to embodiments that have been appropriately changed, replaced, and the like. Moreover, it is also possible to combine the components described in the above embodiment and the components described below to form a new embodiment.

  For example, in the above embodiment, the bobbin 3 is attached to the middle leg portion 42 of the core 4, but the present invention is not limited to this. For example, the technique according to this embodiment may be applied to a type of transformer in which the bobbin 3 is attached to the outer leg portion 43 of the core 4, and the same effect can be obtained.

  Further, for example, in the configuration of the above-described embodiment, the coil body 2 has the bobbin 3 around which the primary winding 21 and the secondary winding 22 are wound, but is not limited thereto. For example, the primary winding 21 that is not wound around the bobbin 3 may be prepared, the additional core 5 may be mounted so as to cover the outside, and the secondary winding 22 may be wound around the outside. . Even in such a configuration, the second closed magnetic circuit 82 similar to that in FIG. 4 is formed, and the same effect as in the above embodiment can be obtained.

  Since the transformer according to the present invention can greatly reduce the heat generation of the transformer, it is extremely useful as a transformer for use in, for example, electrical equipment, power equipment, power converters, and the like used in homes and offices.

A LLC resonance circuit 1 Transformer 2 Coil body 4 Core body 5 Additional core 21 Primary winding 22 Secondary winding 42 Middle leg 43 Outer leg

Claims (5)

A core body having a plurality of legs and a connecting part connecting the plurality of legs, and forming a first closed magnetic path by the plurality of legs and the connecting part;
A coil body attached to the leg of the core body,
The coil body includes a primary winding and a secondary winding arranged around the leg portion in a state of being separated from each other in a radial direction, and a space between the primary winding and the secondary winding. And an additional core that is sandwiched in the entire direction and forms a second closed magnetic path in combination with the leg portion and the connecting portion. The transformer according to claim 1,
The plurality of legs of the core body include a middle leg portion to which the coil body is mounted, and a pair of outer leg portions extending in parallel with the middle leg portion on both sides of the middle leg portion. Transformer. The transformer according to claim 1,
The additional core is a sheet-like core in which a core portion made of a magnetic material and a heat conductive portion having a higher thermal conductivity than the core portion are alternately arranged in the winding direction of the winding. Transformer characterized by The transformer according to claim 2,
The transformer, wherein the coil body has a bobbin around which the primary winding, the additional core, and the secondary winding are wound, and the bobbin is attached to the leg portion. 5. The transformer according to claim 1, a switching unit, and a resonant capacitor, wherein the switching unit receives a DC input voltage, and an output of the switching unit is passed through the resonant capacitor. A resonating unit that is applied to the primary winding of the transformer to resonate;
An LLC resonance circuit comprising: a converter that converts an output voltage obtained from a secondary winding of the transformer into a predetermined DC output voltage and outputs the same.

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