JP2001223106A - Dust core and high-frequency reactor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dust core for a high-frequency reactor having an excellent frequency characteristic and a high magnetic permeability, and a high-frequency reactor that can be manufactured easily at a low cost and improve efficiency. SOLUTION: This dust core is constituted by alloy powder having a composition of 3.0 to 6.0 weight % of Si and 0.1 to 1.0 weight % of O with a remainder of Fe and a grain size of substantially 150 μm or smaller and a binder. Consequently, the ac magnetic permeability μ20kHz is 25 or higher at a dc applied magnetic filed of 1200 A/m, and the iron loss is 1000 kW/m3 under measurement conditions of 20 kHz and 0.1 T.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dust core for a high-frequency reactor which is mounted on a power supply having a switching frequency of 10 kHz or more, among switching power supplies mounted on industrial equipment and general household electric appliances. The present invention relates to a high-frequency reactor using the same.

[0002]

_2. Description of the Related Art In recent years, energy saving and CO2 problems have been increasing, and energy saving measures have been rapidly advanced in general home electric appliances and industrial equipment. In general, a device using a motor such as an air conditioner and a refrigerator, a lighting device, and the like can be cited as devices having a large power consumption and a high energy saving effect. In order to promote energy saving of these products, adoption of high-efficiency motors, high-efficiency electric circuits, and the like are being promoted. Efficiency is a big problem in electric circuits is 50/6
This is a power supply unit that converts 0 Hz AC input into DC. In order to improve the efficiency, switching power supplies have been rapidly spread in recent years.

[0003] However, when a switching power supply is employed, generation of a harmonic current becomes a problem due to distortion of a current waveform. As a countermeasure, various circuit systems have been proposed. For example, choke input method, one-stone converter method, active filter method, etc.
In each case, a reactor is used to increase the conduction angle of the current. In addition to the inductance value, the characteristics required for this reactor are various, such as high conversion efficiency, no undulation in the audible range, small temperature rise, small size and light weight, and low cost.

Although there are various methods for achieving these characteristics, it is conceivable to increase the switching frequency as the most effective means that can be simultaneously solved. In that case,
The reactor material to be used is important, and low loss up to high frequencies, and a relatively large capacity such as an air conditioner, require a high magnetic field and high magnetic permeability, that is, DC superimposition characteristics up to a high magnetic field. From that point of view, whether the current magnetic core material can be applied to these high-frequency reactor materials will be described next.

[0005] First, even if the silicon steel sheet has a high silicon content of 6.5%, if the frequency exceeds 20 kHz, the core loss sharply increases and the magnetic permeability significantly deteriorates.
z or less. In addition, since amorphous requires the use of expensive B and special manufacturing equipment,
This is not a very optimal material because the cost is inevitably increased and the undulation in the audible range is unavoidable due to the large magnetostriction.

[0006] Next, the dust core has the disadvantage that the frequency characteristics are good and the initial permeability is low, but on the other hand, by lowering the initial permeability, the DC superposition characteristics, specifically, the DC applied magnetic field is 400 A / M is good permeability,
It is known that core loss is also relatively low. However, the DC superposition characteristic required for the reactor is 1200 A / m
Because of the high magnetic field in the vicinity and the core loss characteristics are also important, it was impossible to cope with the characteristics of the conventional dust core.

In general, as methods for improving the DC superimposition characteristics, it is conceivable to increase the saturation magnetization of the magnetic core, or to provide a gap in a part of the magnetic path. However, for example, although Japanese Patent Application Laid-Open No. 2-290002 describes a dust core using an Fe-Si alloy powder having a high saturation magnetization,
It is merely about the improvement of the initial magnetic permeability and the frequency characteristics, and there is no description about the improvement of the DC superimposition characteristics and the core loss.

Accordingly, the current large-capacity reactor generally has a switching frequency limited to 20 kHz or less and a magnet wire wound around a magnetic core laminated with a high silicon steel sheet. However, in the future, energy saving, CO
_2. Suppression is an indispensable subject, and it is considered that higher frequency is inevitable even in a large-capacity switching power supply.

[0009]

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a powder magnetic core for a high-frequency reactor which has excellent frequency characteristics and high magnetic permeability, and which can be easily and inexpensively manufactured using the core. It is an object of the present invention to provide a high-frequency reactor capable of improving the performance.

[0010]

Means for Solving the Problems The inventors of the present invention have studied the reactor material in order to achieve the above object, and as a result, have found that the composition is 3.0 to 6.0 wt% Si, 0.1 to 1.0 wt%.
% O, the balance being Fe and having a particle size of substantially 15
By forming a compact from an alloy powder of 0 μm or less and a binder, a powder magnetic core for a high-frequency reactor having excellent DC superimposition characteristics and core loss characteristics and an excellent high-frequency reactor by winding a conductive wire around this core are obtained. Was found to be. More desirably, after mixing the Si-based resin with the magnetic powder, the mixture is molded at a pressure of 10 to ²⁰ t / cm ² , and the molded body is heat-treated at 500 to 1000 ° C. to obtain a high-frequency reactor having more excellent characteristics. It has been found that a dust core for use and a high-frequency reactor can be obtained.

That is, according to the present invention, the composition is 3.0 to 6.0 wt.
% Si, 0.1 to 1.0 wt% O, the balance being Fe, and a powder magnetic core composed of a binder and an alloy powder having a particle size of substantially 150 μm or less, and having an AC magnetic permeability μ
_{20 kHz} is a DC applied magnetic field of 1200 A / m, 25 or more, and iron loss is 100 kHz under the conditions of 20 kHz and 0.1 T.
It is a dust core having a power of 0 kW / m ³ or less.

The present invention also provides a powder magnetic core as described above, wherein a Si-based resin is used as a binder,
/ Cm ^{2 at} a molding pressure of 500 to 1000 ° C. and a heat treatment temperature of 500 to 1000 ° C.
It is a dust core characterized by having a weight of 7.0 g / cm ³ .

The present invention also provides a dust core, wherein 10% or less of the magnetic path length is formed of one or more voids or non-magnetic material in the above-mentioned dust core.

Further, the present invention is a high-frequency reactor characterized in that the above-mentioned dust core is provided with a winding.

In order to improve the DC superimposition characteristics, use a magnetic material having a saturation magnetization as high as possible, and furthermore, make the characteristic that the change of the magnetic permeability relative to the change of the magnetic field becomes as small as possible, that is, the characteristic whose magnetization curve is flat. Need to show. The type of the magnetic material may be a low Si-Fe system, a permalloy PB system, pure iron, or the like, but is substantially limited to a low Si-Fe system in terms of characteristics and cost. Next, to flatten the magnetization curve, there is a method of replacing a part of the magnetic path with a void or a non-magnetic material.However, dust cores originally have a low initial magnetic permeability, so that the required properties are used alone. It is difficult to get.

The inventors of the present invention have found that a lower Si and 0.1 to 1.0 watts than 6.5% Si—Fe showing excellent soft magnetic properties.
It has been found that the magnetization curve of the alloy containing t% O is flatter up to a high magnetic field, and is superior in DC superposition characteristics. This indicates that having an appropriate magnetic anisotropy is more effective for improving the DC bias characteristics, and it is presumed that the O content also has some effect on the appropriate magnetic anisotropy. On the other hand, C increases the coercive force and causes core loss. Therefore, C is desirably 300 ppm or less.

Further, the particle size of the magnetic powder is also very important. If the particle size is large, the initial magnetic permeability increases, but the DC superposition characteristics deteriorate. On the other hand, if the particle size is too small, the magnetic core density decreases. Both the initial magnetic permeability and the DC superposition characteristics cause deterioration. Therefore, when the powder is substantially 150 μm or less, and more desirably, the powder having 20 μm or less is 50 wt% or less, the direct current superposition characteristic shown in the present invention can be obtained.

Furthermore, after mixing the Si-based resin with these powders and molding them under a pressure of 10 to ²⁰ t / cm ² , the molded body is heat-treated at 500 to 1000 ° C., thereby further improving the DC superimposition characteristics and the core loss characteristics. Is obtained. This is achieved by using Si-based resin as a binder.
This is probably because the electrical insulation between the powders was maintained even with the heat treatment at a temperature of 00 ° C. or higher, and the stress strain during powder molding was removed. It is thought that oxygen in the alloy has some influence on the electrical insulation. However, when the heat treatment temperature is 10
When the temperature exceeds 00 ° C., the specific resistance of the magnetic core becomes 0.01 Ω · cm or less, and the core loss characteristic sharply increases.

Further, by replacing less than 10% of the magnetic path of these magnetic cores with an air gap or a non-magnetic material, the flattening of the magnetization curve is promoted and the DC bias characteristics are improved. Because of the increase, the winding generates heat, and as a result, the power conversion efficiency deteriorates.

According to the above-described method, a special device for manufacturing the reactor is not required, so that the reactor can be manufactured easily and inexpensively.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION As a starting material, either an ingot produced by a melting method by mechanical pulverization or a powder produced by an atomizing method can be used without any problem. When the O content of the powder is 0.1 wt% or less, heat treatment is performed in an appropriate oxygen atmosphere and temperature to oxidize the powder surface. Here, since the water atomizing method already contains an appropriate amount of O, the oxidation treatment may be omitted. 15 of this powder
Classification is performed using a sieve of 0 μm, but in order to obtain better characteristics, powder having a size of 20 μm or less must
It is desirably t% or less.

Next, for example, a Si resin is mixed as a binder, and the mixture is compression molded at an appropriate pressure, preferably a pressure of 10 to 20 t / cm ² using, for example, a toroidal mold. Further, the formed body is subjected to a heat treatment at an appropriate temperature, preferably in the range of 500 to 1000 ° C. Next, the number of turns is determined so that a desired inductance value is obtained by using a magnet wire having a wire diameter corresponding to the rated current.

Here, the reason for defining the composition of the alloy is as follows. The reason why the amount of Si is 3.0 to 6.0 wt% is that 3.0% by weight.
If the content is less than wt%, the magnetic anisotropy of the alloy is high and the specific resistance is low, so that the core loss of the magnetic core becomes high.
If the content exceeds 6.0% by weight, the saturation magnetization of the alloy is low, and the hardness is high, so that the density of the compact becomes low and the DC superimposition characteristics deteriorate. The reason why the O content is set to 0.1 to 1.0 wt% is that if the O content is less than 0.1 wt%, the initial magnetic permeability is too high to improve the DC superimposition characteristic. This is because, since the ratio decreases, the saturation magnetization significantly decreases, and the DC superimposition characteristics deteriorate.

Further, when the powder particle diameter is substantially 150 μm or less, the finer the powder, the more the DC superposition characteristics tend to be improved. However, when the powder having a particle diameter of 20 μm or less exceeds 50 wt%, the saturation magnetization is reduced due to the decrease in the density of the compact. This is because the DC superimposition characteristic deteriorates.

As for the molding pressure, when a powder is molded at a pressure of 10 t / cm ² or more using a binder of Si resin, a high compact density of 6.0 g / cm ³ or more and excellent direct current superposition characteristics are obtained. And core loss characteristics are obtained.
A molding pressure exceeding 0 t / cm ² is not realistic because the life of the mold is significantly shortened.

The heat treatment temperature of the compact is 5
When the temperature is higher than 00 ° C., the molding distortion is removed, and the DC superimposition characteristics are improved.
³ , the specific resistance decreases, and the high-frequency characteristics deteriorate significantly. This is presumably because the electrical insulation between the powders is destroyed by sintering, which is a critical difference between the sintered core having a sintered body density ratio exceeding 95% and the dust core according to the present invention.

[0027]

Embodiments of the present invention will be described below.

Example 1 A 3.0 wt% Si-0.5 wt% O-balFe alloy powder produced by a water atomizing method was classified into 150 μm to 20 μm. Here, the powder having a size of 20 μm or less accounted for 9% of the whole powder, and thus was returned to the classified powder. Next, a Si-based resin was used as a binder in a weight ratio of 2.
0 wt% was mixed. Next, using a molding die, the die was formed into a shape having an outer shape of 15 mm, an inner diameter of 10 mm, and a height of 5 mm. Thereafter, the molded body is heated at 800 ° C. in an inert atmosphere.
After holding for 1 hour, the mixture was gradually cooled to room temperature. Next, 1
The next 15 turns and the next 15 turns are wound, and the SY-8232 AC BH tracer of Iwasaki Tsushinki 20kHz,
The magnetic permeability and core loss characteristics at 0.1 T were measured.

As a comparative example, a magnetic core having exactly the same shape was punched out from a 0.1% thick 3% silicon steel sheet with a mold, and then laminated with resin to produce a magnetic core. Next, after performing a strain relief heat treatment, a gap is inserted in the magnetic core so that the DC magnetic permeability μ becomes substantially the same value as in the embodiment, and the primary and secondary windings are performed in exactly the same manner as in the embodiment to perform an alternating current. The magnetic properties were measured. Table 1 shows the results.

[0030]

[Table 1]

As shown in Table 1, it can be seen that the magnetic core manufactured in this example has better magnetic characteristics at high frequencies than the comparative example.

(Example 2) The amount of Si was 2.0, 3.0, 4.
O content is 0.5 ± 0.1 at 0, 5.0, 6.0, 7.0 wt%.
An alloy powder was prepared by a water atomizing method for a composition of a total of 6 lots consisting of wt% and the balance of Fe, and classified into 150 to 20 μm in the same manner as in Example 1. Here, the powder having a particle size of 20 μm or less was 10 wt% or less for all the lots, and thus was returned to the classified powder.

Next, a binder was added to the mixture to give φ60 × φ35.
A magnetic core was formed in a toroidal shape of × φ20 using a mold. Then, after performing a strain relief heat treatment in a nitrogen atmosphere at 850 ° C.,
After winding 90 turns with a magnet wire, the inductance at the time of DC superimposition (1200 A / m) at 20 A
It was measured at kHz. From its inductance value,
The AC permeability was calculated. The result is shown in FIG. FIG. 1 shows that when the amount of Si is 2.0 to 6.0 wt%, μ _{20 kHz}
Shows 25 or more.

Next, when the core loss was measured under the conditions of 20 kHz and 0.1 T, the core loss of the magnetic core other than the 2.0% Si composition was 1000 kW / m ³ or less.

Next, in order to examine the mounting characteristics of these reactors, these reactors were connected to a switching power supply having an output of 2 kW equipped with an active filter in a commercially available air conditioner, and the circuit efficiency was measured. Here, a general electronic load device was connected to the output side. The circuit efficiency was obtained by dividing the output power by the input power. Table 2 shows the results.

[0036]

[Table 2]

From Table 2, for example, a high efficiency of 93% or more can be obtained at 1000 W when the Si content is 3.0 to 6.0 wt.
%, Which means that the core loss is 1000 kW / m ³
It can be seen that the magnetic permeability at 1200 A / m matches the composition range of 25 or more.

(Example 3) A gas atomized powder having a Si content of 4.5 wt% and a balance of Fe alloy was prepared,
After classifying to 20 μm, the O amount was adjusted to 0.05, 0.1, 0.25, 0.2 by adjusting the temperature and the atmosphere appropriately.
5, 0.75, 1.0, and 1.25 wt% of each alloy powder were produced.

Next, a binder was mixed with this alloy in exactly the same manner as in Examples 1 and 2, and a toroidal magnetic core having the same dimensions was produced in exactly the same manner as in Example 2. The magnetic core was wound in exactly the same manner as in Example 1, and the core loss was measured at 20 kHz and 0.1 T. The result is shown in FIG. According to FIG. 2, the O content is 0.1 wt.
%, The core loss sharply deteriorates.

Next, winding was performed in the same manner as in Example 2, and the frequency was changed to 20 kHz at the time of superimposing DC current of 20 A (1200 A / m).
Of the magnetic core having an O content of 1.25 wt% was 1 _{kHz.
Mu 2 0 kHz} of 3,0.05Wt% of core is 23, _{mu 20 kHz} of the other core was 25 or more.

Next, the mounting characteristics of these reactors were measured in exactly the same manner as in Example 2. Table 3 shows the results.

[0042]

[Table 3]

From Table 3, for example, a high efficiency of 93% or more at 1000 W is obtained when the O content is 0.1 to 1.0 wt%.
It can be seen that this is consistent with the composition range in which the core loss is 1000 kW / m ³ or less and μ20 _kHz is 25 or more.

(Example 4) 4.0 w produced in Example 2
t% Si-0.5wt% O-balFe alloy powder,
Using i-based resin as a binder, 1.0, 2.0, and 3.
Powders with binder amounts of 0, 4.0, and 5.0 wt% were prepared. Next, a magnetic core was manufactured in exactly the same manner as in Examples 2 and 3, and the magnetic permeability at the time of DC superposition of 1200 A / m after winding was measured. The result is shown in FIG. Table 4 shows the relationship between the amount of the binder and the density of the magnetic core.

[0045]

[Table 4]

From FIG. 3 and Table 4, the binder amount was 3.0.
It can be seen that, when the magnetic core density is 6.0 g / cm ³ or more, the μ _{20 kHz of} 25 or more can be obtained.

(Example 5) 4.5 w produced in Example 3
The inductance of the reactor wound with 90 turns around a toroidal magnetic core made of t% Si-0.5 wt% O-balFe alloy powder was measured at the time of DC superimposition at 20A.
It was 00 μH. The circuit efficiency was measured by changing the output from 600 W to 2000 W in exactly the same manner as in Example 2.

As a comparative example, a toroidal magnetic core having exactly the same dimensions as above was manufactured using an Fe-based amorphous ribbon having a width of 20 mm. Next, after the heat treatment, a gap was inserted so as to have exactly the same inductance as above, and after winding of 90 turns, the inductance at the time of DC superimposition at 20 A was measured and found to be 520 μH. Further, it was connected to a switching power supply in exactly the same manner as described above, and its circuit efficiency was measured. Table 5 shows the results.

[0049]

[Table 5]

From Table 5, it was found that the reactor according to the present example had higher circuit efficiency than the comparative example. this is,
It is considered that the amorphous magnetic core needs to have a gap, and the leakage magnetic flux in the vicinity of the gap generates heat in the windings and the magnetic core, which adversely affects the efficiency. In addition, it was found that undulation of the magnetic core occurred, and there was a serious problem in practical use.

[0051]

As described above, according to the present invention,
A powder magnetic core for a high-frequency reactor having excellent frequency characteristics and high magnetic permeability, and a high-frequency reactor that can be manufactured easily and inexpensively using the same and that can improve efficiency can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the amount of Si and μ in Example 2.

FIG. 2 is a diagram showing a relationship between an O amount and Pcv in Example 3.

FIG. 3 is a graph showing the relationship between the amount of binder and μ in Example 4.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H01F 37/00 H01F 27/24 K 41/02 D

Claims (4)

[Claims] 1. A composition having a composition of 3.0 to 6.0 wt% Si, 0.1
~ 1.0 wt% O, the balance being Fe, and the particle size is substantially 1
A dust core composed of an alloy powder having a particle size of 50 μm or less and a binder, wherein an AC magnetic permeability μ _{20 kHz} is 25 or more when a DC applied magnetic field is 1200 A / m, and an iron loss is 20 k.
A dust core having a frequency of 1,000 kW / m ³ or less under the conditions of Hz and 0.1 T. 2. The powder magnetic core according to claim 1, wherein a Si-based resin is used as a binder, and the binder is 10 to 20 t / cm ^2.
, And heat-treated at a heat treatment temperature of 500 to 1000 ° C., and the density of the obtained molded body is 6.0 to 7.0 g /
cm ³ , a dust core. 3. The dust core according to claim 1, wherein 10% or less of the magnetic path length is constituted by one or more voids or a non-magnetic material. 4. A high-frequency reactor obtained by winding a dust core according to any one of claims 1 to 3.