JPH11307351A - High frequency transformer and yoke - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce high frequency iron loss, and obtain excellent workability and saturation magnetic flux density, by performing drive at a frequency higher than or equal to 1 kHz and constituting iron core material of a silicon steel plate where the Si concentration of a plate thickness direction surface layer is at least a spcified % higher than that of a central layer. SOLUTION: A driving frequency is 1 kHz. The Si concentration of a plate thickness direction surface layer of a steel plate is set at least 0.3 % higher than that of a central layer. High frequency iron loss can be more restrained as raising the mean value of Si amount, and when the surface Si amount is set 6-7%, high frequency iron loss can be greatly restrained. Concerning magnetostriction, when the surface Si amount is set 6-7%, high frequency magnetic flux flows in the surface layer part, so that magnetostriction is practically made zero up to some degree of magnetic flux density, and noise is reduced. Cracks are hardly generated in a steel plate having the Si concentration gradient, from the matter of punching property, and the number of burrs to be generated at the time of punching is reduced, since the surface layer part is rigid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformer and a yoke used for an inverter and a converter power supply for transportation, industrial equipment, induction heating, electric power, home appliances, information, and the like.

[0002]

2. Description of the Related Art With the recent IGBT inverter technology, the switching frequency is about 10 to 30 kHz.
There is an increasing demand for high-frequency power transformers and yokes used for high-frequency step-up and step-down, insulating transformers, induction heating, ozone generation, and non-contact power supply used inside inverter power supplies. For this reason, reducing the loss of such a transformer or yoke is a point of increasing the efficiency of the inverter power supply or the high-frequency power supply system. For this reason, high-frequency low-loss soft magnetic materials such as ferrite, amorphous and ultra-thin oriented silicon steel sheets, and 6.5% silicon steel sheets have been put to practical use, but their iron loss, cost, durability, and earthquake resistance are high. It cannot be said that they have both.

[0003]

That is, a high-frequency transformer and yoke of 1 kHz to 100 kHz is one
In the case of about kHz, silicon steel sheet, amorphous, 6.5% silicon steel sheet, etc. are used depending on the capacity, application and shape, and ferrite is used from around 10 kHz. Since current loss becomes a problem for both the iron core and the copper wire, it is difficult to select an iron core material in particular. Ferrite, unlike metal-based magnetic materials, has high electrical resistance and can suppress eddy currents, but has problems such as low magnetic flux density, high cost of large-capacity cores, and mechanical brittleness (weak against impact). Amorphous is also a low iron loss material, but high processing cost and shape are limited (thickness 2
(Because it is extremely hard at 5 μm, it is difficult to process other than a wound core.) It is difficult to process into a medium-capacity transformer and yokes of various shapes.

A 6.5% silicon steel sheet is considered to be one of the most suitable core materials, but is somewhat inferior to the conventional non-oriented silicon steel sheet in workability and saturation magnetic flux density. The inventors of the present invention have made intensive efforts to solve such a problem, and as a result, provide Si concentration in the plate thickness direction, specifically, make the silicon content in the surface layer higher than the silicon content in the central portion. It has been found that high frequency iron loss is thereby particularly improved.

The present invention has been made based on this finding, and provides a high-frequency transformer and a yoke which are excellent in high-frequency iron loss and excellent in workability and saturation magnetic flux density.

[0006]

That is, the present invention provides: (1) When the driving is performed at a frequency of 1 kHz or more, the core material is made such that the Si concentration in the surface layer in the thickness direction is 0.3% of the Si concentration in the center layer
Low loss high frequency transformer and yoke made of high silicon steel plate. (2) The low-loss high-frequency transformer and yoke according to (1), wherein the amount of Si in the surface layer of the steel sheet is 6 to 7% and the noise is low.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a steel sheet in a thickness direction.
It has a concentration gradient. There are several methods for providing a Si concentration gradient in the thickness direction as described above. For example, a method of performing heat diffusion after applying a Si paste on the surface of an iron or silicon steel sheet or depositing Si ions by PVD,
Similarly, there is a method of thermal diffusion, or a thermal CVD method (immersion method) of spraying a high-temperature gas such as SiCl ₄ onto a steel sheet to deposit Si and then thermally diffusing the Si. In particular, the last thermal CVD method is the most practical method. FIG. 1 shows the Si concentration distribution in the cross section of the steel sheet produced by this method, and Table 1 shows the representative magnetic characteristics.

[0008]

[Table 1]

In any method, thermal diffusion is necessary to produce a high silicon steel sheet having a uniform Si concentration in the thickness direction, for example, a 6.5% silicon steel sheet having soft magnetic properties. Therefore, there is a disadvantage in manufacturing cost such as increasing the line length and / or suppressing the line speed, or using both of them. Is done. For this reason, there is a cost advantage over a uniform 6.5% silicon steel sheet.

In the present invention, the Si concentration in the surface layer in the thickness direction is 0.3% or more higher than the Si concentration in the center layer. Generally S in iron
As the amount of i increases, the soft magnetic properties improve,
Particularly, the highest value is obtained at 6.5%. However, when the difference in Si concentration between the surface layer and the center is 0.3% or more, the difference in the magnetic permeability between the surface layer portion and the central portion appears. In the case of a uniform Si material, an eddy current flows through the entire surface perpendicular to the direction of the magnetic flux, so that the eddy current loss greatly differs depending on the thickness of the sheet. However, if there is a large difference in the magnetic permeability between the surface layer and the center, the magnetic flux is likely to be confined in the surface layer, and the eddy current flows in two different cross-sections on the front and back surfaces. It can be considered that the effect of pinching is obtained. In this case, this Si
If the concentration difference is less than 0.3%, the effect is small. However, 4%
Exceeding the range is not preferable because the hysteresis loss increases.

It is desirable to increase the average Si amount to suppress high-frequency iron loss, and it is desirable to set the surface Si amount to 6.5% since the high-frequency iron loss can be suppressed most. Further, regarding the magnetostriction, by setting the amount of surface Si to 6.5%, the high-frequency magnetic flux flows through the surface layer, so that when the magnetic flux density is up to a certain level, the magnetostriction becomes substantially zero and low noise. become. This generally means that the driving frequency is 1k
The design magnetic flux density is 0.05T ~
It is about 0.3T, and the 6.5% Si layers on the front and back
It is presumed that the magnetic flux does not sufficiently leak from the front and back portions if it is about 20 to 30%.

Further, from the viewpoint of punching properties, a steel sheet having a Si concentration gradient has ductility at the center and is hardly cracked, so that the surface layer is hard, so that burrs generated at the time of punching can be reduced.

The shape of the transformer core may be a pressed core such as a strip core, a strip laminated block core, a laminated EI core, an EE core, or a UU core, or a wound core such as a toroidal core or a cut core. The laminated iron core has somewhat better iron loss characteristics. However, in the case of a small lot, there is a case where a cut core is more advantageous in assembling cost in coil winding and assembling.

[0014]

EXAMPLES (Example 1) Using the iron core material shown in Table 2, 1
0 kHz, design magnetic flux density 0.06 T, 10 kVA, 1
A prototype of a single-phase transformer having 16 turns each for the second and second turns was prototyped, the no-load loss of the transformer was evaluated by a wattmeter, and noise was measured. As described above, by using the iron core material of the present application, a low-loss, low-noise transformer can be provided.

[0015]

[Table 2] However, the above-mentioned silicon% indicates an average value, and ΔSi indicates a difference between the amounts of Si in the central portion and the surface portion.

[0016]

According to the present invention, it is possible to provide a high-frequency transformer and a yoke which are excellent in high-frequency iron loss and excellent in workability and saturation magnetic flux density.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a Si concentration distribution (sheet thickness 0.1 mm) in a sheet thickness cross section.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Katsushi Kasai 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (2)

[Claims] 1. A low-loss high-frequency transformer and yoke driven at a frequency of 1 kHz or more and made of a silicon steel sheet whose core material has a Si concentration in a surface layer in a thickness direction 0.3% or more higher than a Si concentration in a center layer. 2. The low-loss high-frequency transformer and yoke according to claim 1, wherein the amount of Si in the surface layer of the steel sheet is 6 to 7% and the noise is low.