JP7632200B2 - Core structure and transformer - Google Patents

Description

The present invention relates to the structure of the iron core of a high-frequency, large-capacity transformer, in particular, an iron core made of a ferrite core.

The core of a large-capacity transformer is generally constructed by stacking plate-shaped magnetic bodies, such as ferrite cores, in a frame-like arrangement in one direction (Patent Documents 1 and 2).

Jitszen No. 58-12915 Publication Japanese Patent Application Publication No. 5-326289

In an iron core made of laminated ferrite cores, magnetic resistance caused by the gaps between adjacent ferrite cores causes magnetic flux to concentrate on the inner circumference of the iron core, especially at the joints between the winding and non-winding parts of the iron core, and iron loss also concentrates on this inner circumference.

In view of the above circumstances, the present invention aims to reduce magnetic flux concentration and iron loss on the inner side of the joint between the winding portion and non-winding portion of an iron core made of a ferrite core.

Therefore, one aspect of the present invention is an iron core structure in which the ferrite core has a different cross section at the joint between the winding portion and the non-winding portion of the iron core.

In one aspect of the present invention, in the core structure, the cross section becomes smaller from the outer periphery to the inner periphery of the core.

One aspect of the present invention is a transformer having the above-mentioned core structure.

According to the present invention, it is possible to reduce magnetic flux concentration and iron loss on the inner side of the joint between the winding portion and the non-winding portion of the iron core made of a ferrite core.

FIG. 2 is a cross-sectional view of a core structure in the transformer according to the first embodiment of the present invention. FIG. 2 is an explanatory diagram of the magnetic resistance of a magnetic circuit simulating the outer, middle and inner layers of a transformer core.

The following describes an embodiment of the present invention with reference to the drawings.

The core structure of embodiment 1 shown in FIG. 1 is applied to, for example, a core-type transformer 1.

The transformer 1 has an iron core 2 consisting of ferrite cores 21 to 25, and a primary winding 3 and a secondary winding 4 wound around this iron core 2.

As shown in the figure, the iron core 2 is a hollow rectangular column made up of rectangular or long plate-shaped ferrite cores 21-25 arranged in a frame shape and then stacked in one direction.

The winding section 26, which corresponds to the leg section of the iron core 2 around which the primary winding 3 and secondary winding 4 are wound, and the non-winding section 27, which corresponds to the yoke section of the iron core 2 around which the primary winding 3 and secondary winding 4 are not wound, are made by arranging ferrite cores 21 of the same size and stacking them in one direction. Adjacent ferrite cores 21 are bonded by a bonding method well known in the field of iron core manufacturing.

The corner 28 of the core 2, which is the joint between the winding portion 26 and the non-winding portion 27, is formed by arranging and stacking in one direction a number of ferrite cores 21-25 with different cross sections perpendicular to the axial direction of the core 2. The cross sections become smaller from the outer periphery to the inner periphery of the core 2. Adjacent ferrite cores 21-25 are also bonded by the well-known bonding method.

In the case of the three-layer core 2 illustrated in FIG. 1, the joint 29 has a substantially square cross section. The outer layer OUT (FIG. 2) of this joint 29 contains a ferrite core 21 with a rectangular cross section of normal dimensions and a ferrite core 22 with a rectangular cross section that is approximately 2/3 of the normal dimensions. Furthermore, the middle layer CEN (same figure) located more inward than the outer layer OUT contains ferrite cores 23 and 24 with a cross section that is approximately 1/3 or approximately 1/3 to 4/5 of the cross section of the ferrite core 21. The inner layer IN (same figure) located more inward than the middle layer CEN contains ferrite cores 24 and 25 with a cross section that is approximately 1/3 or approximately 1/10 of the cross section of the ferrite core 21.

In particular, the ferrite cores 21 to 25 are arranged and stacked so that the magnetic resistances of the inner layer IN, middle layer CEN, and outer layer OUT of the iron core 2 are approximately uniform. That is, the magnetic resistance Rm_IN of the inner layer IN, the magnetic resistance Rm_CEN of the middle layer CEN, and the magnetic resistance Rm_OUT of the outer layer OUT of the three-layer iron core 2 illustrated in Figure 2 are expressed by the following formulas (1) to (3) (where μ: magnetic permeability of the iron core 2, l _IN : length of the magnetic path of the inner layer IN, l _CEN : length of the magnetic path of the middle layer CEN, l _OUT : length of the magnetic path of the outer layer OUT, S: cross-sectional area of the magnetic path, μ ₀ : magnetic permeability of a vacuum, l _gap : length of the gap between adjacent ferrite cores 21 to 25 in the inner layer IN, middle layer CEN, and outer layer OUT, S _gap : cross-sectional area of the gap).

Normal magnetic resistance Rm_OUT, magnetic resistance Rm_CEN and magnetic resistance Rm_IN are shown by the following equation (4).

Since the magnetic resistance of the gaps between adjacent ferrite cores 21 to 25 is greater than the magnetic resistance of the ferrite cores 21 to 25, the magnetic resistances Rm_OUT, Rm_CEN, and Rm_IN are adjusted to be approximately equal by adjusting the length and number of the gaps. In particular, since the magnetic resistance rate μ(φ) is a function of the magnetic flux φ, the length and number of the gaps are adjusted by a numerical analysis method such as the finite element method so that the magnetic resistances Rm_OUT, Rm_CEN, and Rm_IN are equal as shown in the following formula (5).

As described above, the ferrite cores 21 to 25 with different cross-sectional dimensions are arranged and stacked so that the gap length between adjacent ferrite cores 21 to 25 becomes smaller as the corners 28 approach from the outer periphery to the inner periphery of the iron core 2. As a result, the number of gaps between the ferrite cores 21 to 25 is smaller on the outside of the iron core 2 and larger on the inside, and the magnetic resistance on the outside and inside is uniform, so the concentration of magnetic flux at the corners 28 of the iron core 2 (the joints between the winding portion 26 and the non-winding portion 27) is mitigated.

There are technical constraints on enlarging the ferrite cores 21 to 25 of the iron core 2, but this can be achieved by arranging and stacking ferrite cores of available sizes. In particular, by equalizing the magnetic resistance by adjusting the number of gaps, it is possible to prevent magnetic flux from concentrating on the inner circumference of the iron core 2, which would otherwise cause iron loss to concentrate on the inside where it is difficult to cool.

The core structure of the above embodiment is applied to a core-type transformer, but it is clear that the same effect as the above embodiment can be obtained by applying the core structure of the present invention to a shell-type transformer as well. Also, while core 2 is a three-layer core, it is clear that the same effect as the above embodiment can be obtained by applying the core structure of the present invention to a core with four or more layers.

1... transformer 2... iron core, 21 to 25... ferrite core, 26... winding portion, 27... non-winding portion, 28... corner portion 3... primary winding 4... secondary winding

Claims (2)

The joint between the winding portion and the non-winding portion of the iron core is made of multiple ferrite cores,
An iron core structure, characterized in that the length of the gap of the ferrite core becomes smaller from the outer layer to the inner layer of the joint . A transformer having the core structure according to claim 1 .

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