JP7085363B2 - Transformer and LLC resonant circuit using it - Google Patents

Description

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

In the LLC resonance circuit, there is known a technique of performing a resonance operation by utilizing a leakage inductance obtained by mounting a transformer with a distance between the primary winding and the secondary winding. For example, in Patent Document 1, the primary winding and the secondary winding are wound at a distance in the longitudinal direction of the bobbin (the direction orthogonal to the winding direction of the winding), and the bobbin is wound around the middle leg of the core. The technique of insertion is disclosed.

Japanese Unexamined Patent Publication No. 2005-333938 International Publication No. 2013/42671

However, when mounted as in Patent Document 1, leakage flux is interlinked with the winding of the transformer, which induces an eddy current loss in the winding (see Patent Document 2). Then, there is a problem that the temperature of the winding rises. In recent years, there has been a demand for a transformer that operates at a high input voltage and a high frequency, so that the problem of temperature rise becomes particularly remarkable.

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 flux interlinking the winding is significantly reduced.

A transformer according to one aspect of the present invention includes a coil body having a core, concentrically wound primary windings and secondary windings, and at least one of the primary winding and the secondary winding. The core includes a core body having a first leg to which the coil body is mounted and a second leg forming a closed magnetic path with the first leg, and the core body. It is characterized by comprising an attached core portion having a third leg portion, which is branched from the above and around which the attached coil is wound.

According to this embodiment, the coil main body for forming the exciting inductance Lm and the attached coil for forming the leakage inductance Lr are separated. The coil main body is attached to the first leg portion of the core main body, and the attached coil is attached to the magnetically separated third leg portion by being branched from the core main body. As a result, the amount of magnetic flux interlinking the windings of the transformer can be significantly reduced as compared with the case where the resonance operation is actively performed by actively utilizing the leakage inductance of the transformer as in the prior art. By doing so, the eddy currents induced in the primary winding and the secondary winding are significantly reduced, and the rise in winding temperature can be significantly reduced.

In the above embodiment, the first leg portion and the third leg portion may have an air gap at an intermediate position in the axial direction, while the second leg portion may be formed continuously and integrally in the axial direction.

This makes it possible to enhance the magnetic separation between the coil main body and the attached coil.

According to the present invention, since the leakage flux interlinking the winding can be remarkably reduced, it is possible to prevent the transformer from excessively generating heat.

It is a perspective view which looked at the transformer which concerns on this embodiment diagonally from the upper side. It is a perspective view which looked at the core from the diagonally upper side. It is an exploded perspective view which looked at the core from the diagonally upper side. FIG. 1 is a sectional view taken along line IV-IV of FIG. It is a figure which shows the structural example of the LLC resonance circuit which concerns on this embodiment. It is a figure which shows the relationship between the applied voltage of a transformer, and the temperature rise.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of preferred embodiments is merely exemplary and is not intended to limit the invention, its applications or its uses.

The transformer according to the present embodiment and the LLC resonance circuit using the transformer can be used as, for example, a power conditioner that converts the generated power of a photovoltaic power generation device and connects it to a commercial power supply system or supplies it to a load. used.

In the transformer according to the present disclosure, (1) the coil for forming the excitation inductance (corresponding to the coil body) and the coil for forming the leakage inductance (corresponding to the attached coil) are physically separated. And, (2) the shape of the core is devised so that the separated coil can be mounted on a single core.

Hereinafter, a specific description will be given.

-Transformer configuration-
As shown in FIG. 1, the transformer 1 includes a coil main body 2, an attached coil 3, and a core 4 to which the coil main body 2 and the attached coil 3 are mounted.

The coil body 2 includes a primary winding 21, a secondary winding 22, and a bobbin 23. The primary winding 21 and the secondary winding 22 are wound around the bobbin 23 so that the coupling coefficient k indicating the degree of mutual coupling of both windings is high. Specifically, the primary winding 21 and the secondary winding 22 are wound concentrically around the coil body 2.

In the bobbin 23, two discs having a circular through hole (not shown) formed in the center thereof are arranged facing each other, and the two discs are connected by a cylindrical bobbin main body (not shown). As a result, the bobbin 23 is formed with an insertion hole (not shown) for inserting the first leg portion 42 of the core 4, which will be described later.

In the following description, the axial direction of the bobbin body of the bobbin 23 is referred to as the vertical direction. In FIGS. 1 to 4, the vertical direction of the bobbin 23 is shown so as to be the vertical direction in the drawings, and for convenience of explanation, "upper" and "lower" are defined according to the drawings.

The coupling coefficient k between the primary winding 21 and the secondary winding 22 is, for example, 0.9 or more and 1 or less, and more preferably 0.97 or more and 1 or less. The coupling coefficient k = 1 indicates a state in which there is no leakage flux. By increasing the coupling coefficient between the primary winding 21 and the secondary winding 22, the magnetic flux interlinking the primary winding 21 and the secondary winding 22 can be reduced, so that the transformer (coil body) can be reduced. The effect of suppressing the heat generation of the coil is obtained.

The winding structure of the coil body 2 is not particularly limited as long as it has a high coupling coefficient k. Generally, in order to increase the coupling coefficient k, it is better that the distance between the primary winding 21 and the secondary winding 22 is short. For example, a so-called sandwich winding structure conventionally known can be applied to this embodiment. The sandwich winding structure is formed between a winding layer formed by one winding (for example, primary winding 21) and a winding layer, and is formed by the other winding (for example, secondary winding 22). It is a structure that sandwiches the winding layer. By doing so, the distance between the primary winding 21 and the secondary winding 22 becomes short in both the vertical direction and the radial direction, and as a result, the coupling coefficient becomes high.

Further, 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 wire diameter of 0.03 to 0.1 mmφ.

When the coupling coefficient between the primary winding 21 and the secondary winding 22 is increased, the leakage inductance Lr generated from the mutual relationship between the primary winding 21 and the secondary winding 22 becomes smaller accordingly. Therefore, in this embodiment, a separation structure is adopted in which the leakage inductance Lr is generated by a separate coil (hereinafter referred to as an accessory coil 3).

The attached coil 3 includes an attached bobbin 31 and an attached winding 32 connected to at least one of the primary winding 21 and the secondary winding 22 by a wiring 24 and wound around the attached bobbin 31.

The attached bobbin 31 has a configuration in which two discs having an oval through hole (not shown) formed in the center are arranged facing each other, and the two discs are connected by a long cylindrical bobbin body (not shown). be. With this configuration, the third leg portion 45 of the core 4, which will be described later, can be inserted.

FIG. 1 shows an example in which the attached winding 32 is connected to the primary winding 21, that is, an example in which the attached coil 3 is attached to the primary side of the transformer 1. The attached winding 32 may be connected to the secondary winding 22, that is, the attached coil 3 may be attached to the secondary side of the transformer 1. Further, the attached coil 3 may be separately attached to both the primary side and the secondary side of the transformer 1. Further, a coupling structure in which the accessory coil on the primary side and the accessory coil on the secondary side are coupled may be used.

The material and diameter of the wire of the attached coil 3 are not particularly limited. For example, it may be common with the primary winding 21 and the secondary winding 22 of the coil body 2. Further, the number of turns of the attached coil 3 is smaller than the number of turns of the primary winding 21 and the secondary winding 22. In the LLC resonance circuit A described later, the leakage inductance Lr is set to be smaller than the excitation inductance Lm, so that the number of turns is set in this embodiment.

2 and 3 are perspective views showing the shape of the core 4, and show the state before mounting the coil main body 2 and the attached coil 3.

As shown in FIGS. 2 and 3, the core 4 includes a core main body 40 and an attached core portion 44 branched from the core main body 40.

The core body 40 has a pair of upper and lower core portions (hereinafter, referred to as an upper core portion 4a and a lower core portion 4b). The upper core portion 4a and the lower core portion 4b have a shape symmetrical with respect to a virtual plane formed at a central position (joining position) in the vertical direction when 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 upside down. Therefore, 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.

As shown in FIG. 3, the lower core portion 4b includes a substantially rectangular plate-shaped base 41 extending in the left-right direction orthogonal to the vertical direction, a first leg portion 42 erected upward on the base 41, and a pair of first legs. It has two legs 43.

The first leg portion 42 has a cylindrical shape and is integrally erected at an intermediate position in the left-right direction of the substrate 41. Further, the cross-sectional shape of the first leg portion 42 is slightly smaller than the opening of the insertion hole of the bobbin 23, and a part or all of the first leg portion 42 is configured to be accommodated in the bobbin main body of the bobbin 23.

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

The base 41 of the lower core portion 4b extends so as to project outward from one of the second leg portions 43 (the second leg portion 43 on the left side in FIG. 3), and the attached coil 3 is attached to the left end thereof. A third leg portion 45 for the purpose is erected.

The shape of the third leg portion 45 is a columnar body having an oblong cross section whose width in the left-right direction is narrower than that of the first leg portion 42. That is, the cross-sectional area of the third leg is equal to or less than the cross-sectional area of the first leg. Since the number of turns of the attached coil is smaller than the number of turns of the primary winding and the secondary winding, and the required inductance value is also small, the third leg portion has such a shape. With such a configuration, the size of the transformer is reduced. The shape of the third leg portion 45 is not limited to a columnar body having an elongated cross section, and may be another shape, for example, a cylindrical shape.

Further, the distance between the second leg portion 43 and the third leg portion 45 on the left side of the drawing is set to be slightly wider than the radial thickness of the attached coil 3 so that the attached coil 3 can be mounted.

The attached core portion 44 in the present disclosure includes an extended portion in which the base 41 extends from the second leg portion 43 and a third leg portion 45. That is, in the configuration of the present embodiment, in the upper core portion 4a and the lower core portion 4b (hereinafter, may be collectively referred to as the upper and lower core portions 4a and 4b), the substrate 41 is common to the core main body 40 and the attached core portion 44. Has been made.

Then, the upper core portion 4a and the lower core portion 4b form the end faces of both core portions 4a and 4b on the open side, that is, the end faces of the first leg portion 42, the second leg portion 43, and the third leg portion 45. They are joined in a state where they are butted against each other.

Here, the height of the first leg portion 42 and the third leg portion 45 in the vertical direction is lower than the height of the second leg portion 43 in the vertical direction. As a result, air gaps Gm and Gr are formed between the upper and lower first leg portions 42 and between the upper and lower third leg portions 45, respectively (see FIGS. 2 and 4).

The air gap Gm formed between the first leg portions 42 of the upper and lower core portions 4a and 4b is an air gap for the exciting inductance Lm formed by the coil main body 2. Further, the air gap Gr formed between the third leg portions 45 of the upper and lower core portions 4a and 4b is an air gap for the leakage inductance Lr formed by the attached coil 3. Further, the heights of the second leg portions 43 on both sides in the left-right direction are aligned with each other so that an air gap is not formed between the second leg portions 43 of the upper and lower core portions 4a and 4b. As a result, as shown by the virtual line in FIG. 4, the magnetic flux can flow, and the exciting inductance Lm formed by the coil main body 2 and the leakage inductance Lr formed by the attached coil 3 can be prevented from being magnetically coupled. ..

In this way, the coil main body 2 and the attached coil 3 are configured as separate coils, and by magnetically separating them from each other, magnetic flux is applied to the windings (wires) of the coil main body 2 and the attached coil 3. Can be prevented from interlinking. This makes it possible to prevent the transformer 1 from excessively generating heat.

-Configuration of LLC resonant circuit-
As shown in FIG. 5, the LLC resonance circuit A receives the power supply voltage Vi from the power supply E at the input terminal IN, converts it into alternating current and outputs the resonance portion 60, and outputs the output of the resonance portion 60 to a predetermined output voltage Vo. It is provided with a conversion unit 62 that converts to and outputs from the output terminal OUT, and a control circuit 7. In the following description, when the positive electrode side and the negative electrode side of the input terminal IN are described separately, they may be described with reference numerals INP and INM. Similarly, when the positive electrode side and the negative electrode side of the output terminal OUT are described separately, OUTP and OUTM may be added to the description.

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

The switching unit 61 has first and second switching elements Q11 and Q12 provided in series between the input terminal INP on the positive electrode side and the input terminal INM on the negative electrode side. FIG. 5 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. 5, and other switching circuits having the same function may be applied.

The resonance capacitors C11 and C12 include a capacitor C11 for current resonance and a capacitor C12 for voltage resonance. The voltage resonance capacitor C12 is connected in parallel to the first switching element Q11. Similarly, a series circuit of the resonance capacitor C11 for current resonance, the attached winding 32, and the primary winding 21 of the transformer 1 is connected in parallel to the first switching element Q11.

In other words, the input terminal INP on the positive electrode side 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 and the attached winding 32. Then, the other end (for example, the winding end) of the primary winding 21 of the transformer 1 is connected to the input terminal INM on the negative electrode side via the second switching element Q12. Further, a closed loop circuit is formed by the first switching element Q11, the first resonance capacitor C11, and the primary winding 21 of the transformer 1.

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 it. Specifically, the conversion unit 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 electrode output terminal OUTP. The diode D22 is connected in the forward direction from one end of the secondary winding 22 of the transformer 1 toward the output terminal OUTP on the positive electrode side. The other end (for example, winding end) of the secondary winding 22 of the transformer 1 is connected to the output terminal OUTM on the negative electrode side.

The conversion unit 62 further includes a backflow prevention diode D21 connected in series between the intermediate node N62 between the second capacitor C21 and the diode D22 and the output terminal OUTM on the negative electrode side. The backflow prevention diode D21 is connected in the direction opposite to the direction from the intermediate node N21 toward the output terminal OUTM on the negative electrode side. Further, an output capacitor C22 is connected between both 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 according to, for example, a program or sequence registered in advance in the 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 61, respectively.

In the present disclosure, the term "connection" includes all things that are electrically connected. That is, the "connection" is not limited to those directly connected, but is a concept including those electrically connected via, for example, a resistance element or a semiconductor element.

FIG. 6 shows a primary winding of an LLC resonance circuit (hereinafter referred to as an implementation circuit) 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 without an attached coil. It is a figure which compared the temperature rise of. In FIG. 6, circles are the results of the implementation circuit and triangles are the results of the comparison circuit.

In FIG. 6, 270V and 330V are applied as the power supply voltage Vi, and the temperature of the primary winding 21 is measured using a thermocouple after a lapse of a predetermined time. Further, the comparison circuit uses a PQ type core, and a leakage inductance is generated by shifting the winding position between the primary winding and the secondary winding of the coil body in the axial direction. ..

As shown in FIG. 6, in the comparison circuit, the primary winding temperature reaches 89 degrees at 270 V and 110 degrees at 330 V, whereas in the implementation circuit, 1 at both 270 V and 330 V. The next winding temperature is about 65 degrees, and the temperature rise is remarkably reduced.

Furthermore, the inventor measured the leakage flux of the implementing circuit and the comparison circuit. As a method of measuring the leakage flux, the measuring coil was brought close to the transformer while the transformer was energized, and the induced voltage induced in the measuring coil was measured. As a result, it was confirmed that the induced voltage was reduced to about 1/9 of that of the comparison circuit, and that the magnetic flux leakage to the outside of the transformer was significantly reduced in the implementation circuit.

As described above, according to the present embodiment, the coil main body 2 for forming the exciting inductance Lm and the attached coil 3 for forming the leakage inductance Lr are separated. The coil main body 2 is attached to the first leg portion 42 of the core main body 40, and the attached coil 3 is attached to the third leg portion 45 magnetically separated from the core main body 40. With such a configuration, the amount of magnetic flux interlinking with the winding of the transformer 1 is significantly reduced as compared with the case where the resonance operation is positively performed by utilizing the leakage inductance of the transformer as in the prior art. can do. In the prior art, the leakage flux is interlinked with the winding of the transformer, so that a vortex current loss is induced in the winding and the winding temperature rises. However, in the configuration of the present embodiment, the leakage flux is wound. Since the leakage inductance can be obtained without interlinking with the wire, such temperature rise can be significantly reduced.

<Other embodiments>
Although the preferred embodiment of the present invention and its modifications have been described above, the technique according to the present disclosure is not limited to this, and can be applied to an embodiment in which modifications, replacements, etc. are appropriately performed. Further, 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 air gap Gm is formed between the first leg portions 42 of the upper and lower core portions 4a and 4b, that is, is formed at an intermediate position in the vertical direction of the transformer 1. Not limited to. For example, the air gap Gm may be formed at the boundary portion between the substrate 41 and the upper core portion 4a or the lower core portion 4b. The same applies to the air gap Gr, and the air gap Gr may be formed at the boundary portion between the substrate 41 and the upper core portion 4a or the lower core portion 4b instead of the intermediate position in the vertical direction of the transformer 1. ..

Since the transformer according to the present invention can significantly reduce the heat generation of the transformer, it is extremely useful as a transformer used for, for example, electric equipment, power supply equipment, power conversion equipment and the like used in homes and offices.

A LLC Resonance Circuit 1 Transformer 2 Coil Body 3 Attached Coil 4 Core 21 Primary Winding 22 Secondary Winding 40 Core Body 42 1st Leg 43 2nd Leg 44 Attached Core 45 3rd Leg

Claims (5)

With the core
A top-view circular coil body with concentrically wound primary and secondary windings,
It comprises an accessory coil connected to at least one of the primary winding and the secondary winding.
The core is branched from a core body having a first leg portion to which the coil body is mounted and a second leg portion forming a closed magnetic path with the first leg portion, and the accessory coil is mounted. With an attached core part having a third leg part ,
The upper ends and the lower ends of the first leg, the second leg, and the third leg are connected to each other by a plate-shaped substrate.
The second leg includes a middle leg provided between the first leg and the third leg.
The middle leg portion has a wall surface facing the coil body recessed in an arc shape so as to follow the outer shape of the coil body.
The number of turns of the attached coil is smaller than the number of turns of the primary winding and the secondary winding.
The third leg portion is a transformer characterized in that the width of each leg portion in the arrangement direction is narrower than that of the first leg portion . In the transformer according to claim 1,
The width of the third leg portion in the front-rear direction orthogonal to the arrangement direction is wider than that of the first leg portion.
A transformer characterized by that. In the transformer according to claim 1 ,
The transformer is characterized in that the first leg portion and the third leg portion have an air gap at an intermediate position in the axial direction, while the second leg portion is continuously and integrally formed in the axial direction. In the transformer according to claim 1 or 2 .
A transformer characterized in that the cross-sectional area of the third leg portion is equal to or smaller than the cross-sectional area of the first leg portion. The transformer, the switching unit, and the resonance capacitor according to any one of claims 1 to 4 are provided, a DC input voltage is received by the switching unit, and the output of the switching unit is transmitted via the resonance capacitor. A resonance part that is applied to the primary winding of the transformer to resonate,
An LLC resonant circuit comprising a conversion unit that converts an output voltage obtained from the secondary winding of the transformer into a predetermined DC output voltage and outputs the voltage.

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