JP2020161514A - Method of predicting characteristics of coil component - Google Patents

Abstract

To provide a method of predicting coil components' characteristics to facilitate the design of coil components with cores containing magnetic materials with high saturation magnetic flux density.SOLUTION: A long, thin bar-shaped sample is made of the material that makes up a core of a coil component. The sample's magnetic properties are measured by a vibrating sample magnetometer (VSM) until it is almost completely saturated with magnetism. The results are used to predict the characteristics of the coil components by simulation.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for predicting characteristics of coil components.

In recent years, coil parts for applications where a large current is energized are required to have a larger current in addition to miniaturization. In order to increase the current, it is necessary to construct the core using a magnetic material that is not easily magnetically saturated with respect to the current. Therefore, as the magnetic material, an iron-based metal magnetic material is used instead of the ferrite-based material. Is becoming.

Comparing the metallic magnetic material with the ferrite-based soft magnetic material, for example, as described in Patent Document 1, in the BH curve, the magnetic flux density continues to increase without being saturated up to a higher magnetic field, and with respect to the current. It is characterized by a low rate of decrease in self-inductance.

Due to the widespread use of such metallic magnetic materials, there are increasing cases where it is not necessary to pay attention to conventional ferrite-based materials, which becomes a new issue.
For example, in a simulation at the time of coil component design, it is difficult to predict the characteristics and behavior of the element when a large current is applied. This is because when the current flowing through the inductor is increased, the conductor that is the path of the current is destroyed by the heat generated by its own resistance before the metal magnetic material that is the core is magnetically saturated, and a large current is passed. This is due to the difficulty in measuring the characteristics of the core. As described in Patent Document 2 and the like, characteristic values such as inductance in coil components (inductors) change depending on the applied DC current, so in order to obtain accurate simulation results, when a large current is applied, It is necessary to accurately grasp the characteristics of the core.
In a coil component provided with a ferritic soft magnetic material as the core, the core is magnetically saturated with a current smaller than the current value at which the conductor is destroyed by resistance heat generation, and it is easy to actually measure the characteristics of the core. No problem occurred.

Japanese Unexamined Patent Publication No. 11-214229 International Publication No. 2014/185294

Conventionally, in order to acquire the characteristic data of the core when a large current is passed, in order to suppress heat generation, the dimensions of the core, the dimensions of the conductor, the number of turns, etc. are designed according to the type of the material constituting the core. Therefore, it was necessary to prepare a toroidal for acquiring characteristic data. For this reason, it takes time and effort to acquire data, and there is a problem that simulation for device design cannot be easily performed.

Therefore, an object of the present invention is to provide a method for predicting the characteristics of a coil component, which solves the above-mentioned problems and facilitates the design of a coil component including a core containing a magnetic material having a large saturation magnetic flux density.

As a result of various studies to solve the above problems, the present inventor prepared an elongated rod-shaped sample from the material constituting the core of the coil component, and used the vibrating sample magnetometer for the sample. : VSM) was used to measure the magnetic properties until the magnetism was almost completely saturated, and it was found that the problem could be solved by performing a simulation using this result, and the present invention was completed.

That is, an embodiment of the present invention for solving the above problems is a method for predicting the characteristics of a coil component including a core formed of a magnetic material having a saturation magnetic flux density of 1.5 T or more, and is formed of the magnetic material. Prepare a measurement sample having an aspect ratio of 3 or more, and use a vibrating sample magnetometer (VSM) to determine the relationship between the magnetic field (H) applied to the measurement sample and the magnetic flux density (B) of the sample. To measure, to calculate the BH curve and μ-B curve from the measurement result, and to separately prepare a coil having a toroidal core having the same composition as the measurement sample and energize the coil. Measured the relationship between the magnetic field (H) and the magnetic flux density (B), and the magnetic permeability of the coil at a DC current of 0 A, the differential magnetic permeability at H = 0 A / m and the minor loop obtained from the VSM measurement. The demagnetic flux coefficient is calculated so that the slopes of the above are the same, and the BH curve and the μ-B curve are corrected by the demagnetizing magnetic flux coefficient, and the BH curve and the μB curve are used. This is a method for predicting the characteristics of a coil component, including calculating the characteristics of the coil component by the finite element method.

According to the present invention, it is possible to accurately and easily design a coil component including a core made of a magnetic material having a high saturation magnetic flux density.

A graph showing a BH curve obtained for a rod-shaped sample according to an embodiment of the present invention and a BH curve obtained by a conventional measurement method using a toroidal. A graph showing a μ-B curve obtained for a rod-shaped sample according to an embodiment of the present invention and a μ-B curve obtained by a conventional measurement method using a toroidal. A graph showing the change in inductance with respect to the current value obtained by the simulation according to the embodiment of the present invention and the change in inductance with respect to the current value obtained by the conventional simulation.

Hereinafter, the configuration and the action and effect of the present invention will be described with technical ideas. However, among the components in the following embodiments, the components not described in the independent claims indicating the highest level concept are described as arbitrary components.

The method for predicting the characteristics of coil components according to an embodiment of the present invention (hereinafter, simply referred to as "the present embodiment") is applied to an inductor having a core formed of a magnetic material having a saturation magnetic flux density of 1.5 T or more. A magnetic flux (H) applied to the measurement sample by a vibrating sample magnetometer (VSM) and the sample are prepared, which are formed of the magnetic material and have an aspect ratio of 3 or more. To measure the relationship with the magnetic flux density (B), calculate the BH curve and μB curve from the measurement results, and separately provide a coil with a toroidal core having the same composition as the measurement sample. By preparing and energizing the coil, the relationship between the magnetic field (H) and the magnetic flux density (B) was measured, and the magnetic permeability of the coil at a DC current of 0 A was obtained from the VSM measurement. The demagnetizing magnetic flux is calculated so that the differential magnetic flux density at 0 A / m and the inclination of the minor loop match, and the BH curve and the μB curve are corrected by the demagnetizing coefficient, and the B− Includes calculating the characteristics of coil components by the finite element method using the H curve and the μ-B curve.

[Magnetic material]
The magnetic material used in this embodiment has a saturation magnetic flux density of 1.5 T or more. Examples of such a magnetic material include a metal containing Fe or Ni as a main component. The metal containing Fe as a main component may contain at least one or more of Si, Cr, Al, Ni, and Co. Further, the magnetic material may be crystalline or amorphous. Specific examples of the crystalline metallic magnetic material include Fe, FeSi, FeSiCr and FeSiAl, and specific examples of the amorphous metallic magnetic material include FeSiCrB and FeSiPBC.

This embodiment is suitable when a metallic magnetic material having an Fe content of 94 mass% or more is used. This is because such magnetic materials require a particularly large magnetic field for magnetic saturation, making it difficult to apply conventional methods for obtaining core characteristic data from toroidals when a large current is applied. .. Further, for the same reason, the present embodiment is also suitable when a magnetic material having an initial magnetic permeability of 10 or less is used.

[Sample for measurement]
The measurement sample used in this embodiment is made of the above-mentioned magnetic material and has an aspect ratio of 3 or more. By applying a magnetic field in the direction in which the aspect ratio of the measurement sample is large, magnetic flux can efficiently pass through the measurement sample, and magnetic saturation is likely to occur. The aspect ratio is preferably 5 or more, and more preferably 7 or more. At this time, the length of the measurement sample in the major axis direction is set in the measurement area of the vibrating sample magnetometer (VSM) used for measuring the relationship between the magnetic field (H) and the magnetic flux density (B) of the sample, which will be described later. Set to fit. The measurement area does not simply mean a region where the measurement sample can be physically accommodated, but a region where the magnetic field distribution becomes uniform.
The shape of the measurement sample may be rod-shaped, but a spheroidal shape is preferable from the viewpoint of facilitating demagnetic field correction described later.

The measurement sample shall have the same composition and microstructure as the core of the coil component for which the characteristics are to be predicted. Therefore, the measurement sample is manufactured according to the general core manufacturing method exemplified below.

When manufacturing the core of a coil component, a powdery or granular magnetic material (hereinafter, collectively referred to as "powder", and individual particles constituting the powder) are used as a magnetic material. .. The magnetic material powder may have a single composition or may be a mixture of powders having different compositions. Further, it may be a mixture of powders having different particle sizes. When the core is formed of a magnetic material having a single composition, it becomes a highly uniform magnetic material. When a magnetic material containing Fe as a main component and powders or particles having different compositions are mixed to form a core, the particle size of the particles containing a large amount of Si is increased, and the particle size of the particles containing a large amount of Ni or Co is increased. It is preferable to reduce the size.

Magnetic material powders are usually provided with an insulating layer on the particle surface for electrical insulation. The insulating layer may be an organic material or an inorganic material as long as it can impart the desired insulating property. When the insulating layer is made of an organic material, it is preferable in that high impact resistance can be obtained. On the other hand, when the insulating layer is made of an inorganic material, it is preferable in that high heat resistance can be obtained. Examples of the organic material that can be used include thermosetting resins such as epoxy, phenol, silicone and polyimide. Examples of the inorganic material that can be used include a phosphoric acid-based chemical conversion film, a chromium-based chemical conversion film, a glass film, an oxide film, and the like.

In the production of the core from the magnetic material powder, the powder is mixed, the resin is further added and kneaded, and after molding into the desired shape, the resin is cured by heating or the resin is volatilized by heating. After removal, heat treatment is performed to bond the particles together.
The resin used is a thermosetting resin such as epoxy, phenol, silicone and polyimide when it is cured by heating. From the viewpoint of obtaining a core having high mechanical strength, a core having a high molecular weight is preferable. On the other hand, when the resin is removed by heating, polyvinyl alcohol (PVA), polyvinyl butyral (PVB), acrylic and the like are preferable because they are easily thermally decomposed and carbides are less likely to remain. The amount of the resin added is not limited, but as an example, it can be about 1 mass% to 5 mass% with respect to the magnetic material powder.
The method for molding the core is not particularly limited, and a method of pressure molding a mixture of magnetic material powder and resin using a mold, a method of combining this with polishing, and the like can be adopted. Further, a method of cutting out a molded product from a sheet formed of a mixture of magnetic material powder and resin by laser processing, dicing or the like may be adopted.
The heating temperature at which the resin is cured after molding may be determined according to the properties of the resin used, but can be approximately 150 ° C.
The degreasing temperature when the resin is removed after molding is set according to the decomposition temperature of the resin used, but is generally about 200 ° C. to 500 ° C. Further, the degreasing atmosphere is preferably superheated steam in order to prevent oxidation of the magnetic material powder. Further, the heat treatment after removing the resin may be performed in an air atmosphere or an inert gas atmosphere. Examples of the inert gas atmosphere include nitrogen, rare gases such as helium and argon, and vacuum. The heat treatment temperature can be 400 ° C. or higher or 500 ° C. or higher, and 850 ° C. or lower or 750 ° C. or lower. The heat treatment time can be 60 minutes or more when the heat treatment temperature is 650 ° C. or lower, and less than 60 minutes when the heat treatment temperature exceeds 650 ° C. When a mixture of powders having different compositions is used as the magnetic material powder, it is preferable to perform heat treatment at a relatively high temperature in an inert atmosphere from the viewpoint of removing strain in the core.

In the manufactured core, the magnetic material particles are bonded to each other by a binder such as resin, glass or oxide. In the core manufactured by curing the resin, the magnetic material particles are bonded by the resin, and the core has excellent impact resistance. On the other hand, in the core produced by heat treatment after removing the resin, the magnetic material particles are bonded with glass or oxide, and the core has excellent heat resistance.

[Measurement of magnetic field (H) and magnetic flux density (B) of measurement sample]
In this embodiment, the relationship between the magnetic field (H) applied to the measurement sample and the magnetic flux density (B) is measured by a vibrating sample magnetometer (VSM). Since the VSM applies a magnetic field from the outside of the sample for measurement, it is not necessary to pass a current through the sample itself. Therefore, since it is not necessary to provide a conductor in the sample, it is not necessary to devise the structure of the sample so that the conductor does not break even if a current is applied until the sample is magnetically saturated.

The measurement is performed on the major loop and the minor loop starting from any point on the initial magnetization curve.
The measurement of the major loop is performed up to the maximum applied magnetic field in which the change in magnetic permeability (μ) with respect to the change in magnetic field strength becomes sufficiently small. The maximum applied magnetic field is preferably a magnetic field in which the value of μ is 90% lower than the initial magnetic permeability (10% of the initial μ). In the maximum applied magnetic field, the sample can be considered to be substantially magnetically saturated. The amount of change in the magnetic field for each measurement depends on the size of the sample and the like, but is set to about 5000 A / m, or about 100 A / m for finer measurement. In order to improve the accuracy of the simulation, it is better to reduce the amount of change in the magnetic field for each measurement, but as the amount of change is reduced, the number of measurement points increases and the measurement takes time. Therefore, the amount of change in the magnetic field for each measurement may be set so that measurement data of about 20 points or more can be obtained, and it is not necessary to make the amount of change excessively fine.
The minor loop may be measured by selecting an arbitrary score from the initial magnetization curve up to the maximum applied magnetic field described above. In order to express the μ-B curve, the number of measurement points is preferably 20 points or more, and more preferably 30 points or more. It is not necessary to make the intervals between the measurement points even, and the measurement may be performed finely especially where the μ value changes significantly. Further, the demagnetization width needs to be a magnetic field condition that does not deviate from the initial magnetic permeability, and is preferably 500 A / m to 2000 A / m. By setting the value to 500 A / m or more, the error due to noise can be reduced, and by setting the value to 2000 A / m or less, the deviation from the initial magnetic permeability can be suppressed.

[Calculation of BH curve]
An averaged BH curve is calculated from the round-trip value of the major loop measured by the VSM.

[Calculation of μ-B curve]
The incremental magnetic permeability (ΔB / ΔH) at each measurement point is calculated from the slope of the minor loop measured by the VSM, and the μ−B curve is calculated from the relationship between this and the magnetic flux density.

[Demagnetic field correction]
The BH curve and the μB curve calculated by the method described above include the influence of the demagnetic field (shape factor) due to the shape of the sample for measurement. Therefore, in order to remove the influence of the demagnetic field from the BH curve and the μB curve and to reflect the characteristics of the material itself more, the demagnetic field correction is performed in this embodiment. The demagnetic field correction is a coil formed of the same material as the measurement sample, that is, a coil having a toroidal core having the same composition, the same particle size, and the same density (hereinafter, simply referred to as "toroidal"). Prepare and perform as follows. The above-mentioned same particle size means that the average particle size is within ± 10%, and can be within ± 5% by using, for example, the same lot of material as the measurement sample. Further, the above-mentioned same density means within ± 3%, and can be made within ± 1% by, for example, processing a measurement sample and a toroidal core from the same molded product.
The demagnetic field correction of the BH curve was determined so that the differential magnetic permeability (dB / dH) calculated from the curve at H = 0 matches the magnetic permeability at the DC current 0A actually measured for the toroidal. This is done using the demagnetic field coefficient.
Further, in the demagnetic field correction of the μ-B curve, the demagnetic field coefficient is determined so that the slope of the minor loop at H = 0 matches the magnetic permeability at the direct current 0A actually measured for the toroidal, and each of these is determined. It is performed by recalculating the magnetic permeability at each measurement point by reflecting it in the minor loop.

[Calculation of inductor characteristics by the finite element method]
In the present embodiment, the coil parts are simulated based on the obtained BH curve and μB curve. The simulation is performed by using the finite element method (FEM), creating a model based on the size and conductor dimensions of the coil parts, and then applying the numerical values obtained from the BH curve and μB curve to the model. ..
By simulation, changes in various characteristics such as inductance with respect to current can be obtained. It is preferable to perform the simulation until the current value per unit volume becomes 20 A / mm ³ or more, because the behavior when the coil component is magnetically saturated can be grasped.
In addition, the accuracy of the simulation can be improved by comparing the results obtained by the simulation with the results actually measured for the actual coil parts and fitting the BH curve and μB curve so that the difference between the two is small. It is preferable in that it can be improved.
In addition, a part or all of the above-mentioned measurement and calculation may be executed programmatically using a dedicated or general-purpose computer.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the Examples.

[Preparation of measurement sample and demagnetic field correction sample]
As a magnetic material powder, a Fe-Si-Al alloy having an average particle size of 20 μm (containing 3.5% by mass of Si and 1.0% by mass of Al, and the balance is Fe and impurities) is prepared, and a binder is added thereto. The added composite magnetic material was processed into a sheet. From the sheet, a rod-shaped measurement sample and a toroidal-shaped core used for the demagnetic field correction sample were prepared.
The rod-shaped measurement sample was prepared by cutting out from the above-mentioned sheet so as to have a major axis of 4 mm and a minor axis of 0.5 mm.
The toroidal core was produced by punching from the above-mentioned sheet so that the outer diameter was 20 mm and the inner diameter was 12 mm. A 0.3 mmφ urethane-coated lead wire was wound around the outer circumference of the obtained core 40 times to prepare a sample for demagnetic field correction.

[Calculation of BH curve and μB curve]
First, for toroidal, which is a sample for demagnetic field correction, the magnetic permeability and the rate of change thereof were measured using an LCR meter (E4980A manufactured by Keysight) with a direct current in the range of 0A to 10A. The AC signal at this time was set to 100 kHz and 2 mA. The obtained value of magnetic permeability at a direct current of 0 A was used when performing the following demagnetic field correction.

Next, for the rod-shaped magnetic material, a major loop measurement was performed in a range of an applied magnetic field of ± 1000 kA / m in 1 kA / m increments using a VSM measuring instrument (BHV-35, RIKEN Electronics Co., Ltd.). From the obtained major loops, BH curves of 1000 kA / m to 0 A / m, 0 A / m to −1000 kA / m, −1000 kA / m to 0 A / m and 0 A / m to 1000 kA / m were averaged. From this, the differential magnetic permeability from 0A / m to 1000A / m is calculated, and the demagnetic field coefficient is obtained so that this value becomes the same value as the magnetic permeability at the toroidal DC current of 0A described above, and B By correcting the −H curve, a B—H curve from which the shape factor was removed was obtained. The obtained BH curve is shown in FIG. The figure also shows the results obtained by the conventional measurement method using toroidal.
From FIG. 1, it can be seen that in the present invention using the VSM measuring instrument, a BH curve until the magnetic material is substantially magnetically saturated can be obtained.

In addition, for rod-shaped magnetic materials, a VSM measuring instrument is used to demagnetize 1 kA / m from the state where a magnetic field is applied at 30 points in the range of 0 A / m to 1000 kA / m to perform minor loop measurement. went. Then, the incremental magnetic permeability is calculated by performing demagnetic correction on the measurement results at each point so that the inclination of the minor loop at 0 A / m becomes equal to the magnetic permeability of the toroidal DC current of 0 A described above. Then, the μ-B curve was calculated. The obtained μ-B curve is shown in FIG. The figure also shows the results obtained by the conventional measurement method using toroidal.
From FIG. 2, in the present invention using a VSM measuring instrument, it is possible to obtain a μ-B curve from the initial magnetic permeability to a decrease of 90% or more (10% or less of the initial μ) of the μ value of the magnetic material. I understand.

[Simulation of coil parts]
Based on the obtained numerical values of the BH curve and the μB curve, the coil parts were simulated by the finite element method. The simulation model was a coil in which a polyurethane-coated copper wire having a diameter of 0.15 mm was wound around a core having external dimensions of 2.0 mm × 1.6 mm × 1.0 mm for 6 turns. FIG. 3 shows the relationship between the rate of change of inductance with respect to the current obtained as a result of the simulation. The figure also shows the simulation results based on the numerical values of the BH curve and the μB curve obtained by the conventional measurement method using toroidal.
From FIG. 3, according to the present invention, when the direct current flowing through the coil component is small, a result that is in good agreement with the conventional simulation result can be obtained, and the coil component is difficult to calculate by the conventional method. It can be seen that it is possible to simulate up to a large current value in which the inductance of the coil is almost completely reduced. That is, according to the present invention, the region where the coil component breaks can be known by simulation.

According to the present invention, even for a coil component having a core made of a magnetic material having a high saturation magnetic flux density, the characteristics or behavior until magnetic saturation can be predicted by a simple method. Therefore, the present invention is useful in that the DC superimposition characteristics of the coil component when a large current flows and the effect of this on the circuit can be easily grasped, and the coil component can be efficiently designed. It is a thing.

Claims (6)

A method for predicting the characteristics of a coil component having a core made of a magnetic material having a saturation magnetic flux density of 1.5 T or more.
To prepare a measurement sample formed of the magnetic material and having an aspect ratio of 3 or more.
To measure the relationship between the magnetic field (H) applied to the measurement sample and the magnetic flux density (B) of the sample with a vibrating sample magnetometer (VSM).
To calculate the BH curve and the μB curve from the measurement results,
A coil having a toroidal core made of the same material as the measurement sample is separately prepared, and the relationship between the magnetic field (H) and the magnetic flux density (B) is measured by energizing the coil, and the DC current of the coil is measured. The demagnetic field coefficient was calculated so that the magnetic permeability at 0A coincided with the differential magnetic permeability at H = 0A / m and the inclination of the minor loop obtained from the VSM measurement, and the demagnetic field coefficient was used to calculate the B-. Modifying the H-curve and the μ-B curve, and calculating the characteristics of the coil component by the finite element method using the B-H curve and the μ-B curve.
Methods for predicting the characteristics of coil components, including. The method for predicting the characteristics of a coil component according to claim 1, wherein the magnetic material is a metallic magnetic material having an Fe content of 94 mass% or more. The specific prediction method for a coil component according to claim 1 or 2, wherein the initial magnetic permeability of the magnetic material is 10 or less. The characteristics of the coil component obtained by the characteristic prediction method are compared with the characteristics of the actually manufactured coil component, and the BH curve and the μB curve are further modified so that both characteristics match. The method for predicting characteristics of an inductor according to any one of claims 1 to 3, which includes. The method for predicting the characteristics of a coil component according to any one of claims 1 to 4, wherein the measurement by the VSM is performed in a range from the initial magnetic permeability to a decrease of 90%. The method for predicting the characteristics of a coil component according to any one of claims 1 to 5, wherein the characteristic calculation of the coil component is performed under the condition that the current value per unit volume is 20 A / mm ³ or more.