Switched reluctance motor

Abstract

To provide a switched reluctance motor capable of achieving a high-torque characteristic and a low noise.SOLUTION: A switched reluctance motor is constructed by a rotor having a plurality of salient poles which does not have a wiring and a stator that includes each salient pole having the wiring to a direction that is opposite to each salient pole of the rotor. A ratio of a front surface area SRT of a magnetic pole in each salient pole of the rotor and a front surface area SST of the magnetic pole in each salient pole of the stator satisfies 2.0×BM≤(SST / SRT)≤3.5×BM to a magnetic flux density BM that a soft magnetic material to be used for an iron core material indicates the maximum permeability.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a switched reluctance motor.

Background Art

[0002] In recent years, in the automotive field, electrification has been progressing for CO 2 emission suppression, and it is predicted that electrification will continue to progress in the future. Here, from the viewpoint of suppressing energy consumption of the motor serving as the driving force source, higher efficiency is required. Further, from the viewpoint of mountability on an automobile, miniaturization of the motor is required.

[0003] An interior permanent magnet motor (IPM) is often adopted as a drive motor for an electric vehicle. This is an effective motor type for achieving high efficiency under a wide range of operating conditions such as an automobile. On the other hand, the interior permanent magnet motor has a problem that the cost is high because a large amount of magnets (permanent magnets) are used. Further, it is predicted that not only the cost of the magnet is high but also a risk of resource depletion occurs because a large amount of rare earths such as neodymium or dysprosium are used. Therefore, the importance of configuring a drive motor for an automobile in a motor type that does not use a magnet is increasing.

[0004] As motor types that do not use magnets, induction motors (IMs), switched reluctance motors (SRMs), synchronous reluctance motors (SynRMs), etc. are known. Since induction motors use conductors such as copper and aluminum in the rotor, although they are not as resource-intensive as magnets, they have a large resource load. In addition, since secondary copper loss occurs in the rotor, it is difficult to achieve high efficiency. Synchronous reluctance motors have a complex shape in order to achieve a rotor structure that provides a difference in inductance between the d-axis and q-axis, and the use of a high-strength soft magnetic material is required for the rotor core. Here, generally, in order to improve torque characteristics in a motor, the width of a portion called a bridge may be narrowed. In a synchronous reluctance motor, when the width of the bridge is narrowed, even if a high-strength electromagnetic steel sheet is used, it cannot withstand high-speed rotation, and the rotor may be damaged by centrifugal force. On the other hand, in a switched reluctance motor, the rotor structure is relatively simple, high strength is not necessarily required for the core material, and secondary copper loss does not occur. Therefore, a switched reluctance motor can achieve high efficiency. However, switched reluctance motors generally have inferior torque characteristics compared to embedded magnet motors and have the problem of generating a large amount of noise.

[0005] In response to this problem, for example, Patent Document 1 proposes to utilize an electromagnetic steel sheet having magnetic anisotropy as a core material and effectively pass magnetic flux through the magnetic poles to increase torque. However, adopting a material having magnetic anisotropy for the core material causes non-uniformity of the magnetic flux flowing in the motor core, which may promote the time variation of the electromagnetic force and increase motor noise. Here, Non-Patent Document 1 describes the influence of magnetic strain of the core material in a switched reluctance motor. According to Non-Patent Document 1, it is possible to reduce the noise of the motor by adopting 6.5% Si steel, which is a zero magnetic strain material, as the core material. However, since 6.5% Si steel has a low saturation magnetic flux density, it is a core material that is disadvantageous for increasing the torque of the motor.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Non-Patent Document

[0007]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The difficulty of achieving both high torque and noise reduction is not limited to motors for automotive drive applications, but also appears in motors for various applications such as home appliances, hindering the electrification for realizing a carbon-neutral society.

[0009] In view of such circumstances, an object of the present disclosure is to provide a switched reluctance motor that achieves high torque characteristics and low noise in a switched reluctance motor that does not use permanent magnets.

Means for Solving the Problems

[0010] The inventors of the present invention have conducted intensive studies to achieve the above problems. As a result, the surface area S of the magnetic poles at the salient poles of the rotor RT , the surface area S of the magnetic poles at the salient poles of the stator ST and the magnetic flux density B indicating the maximum magnetic permeability of the soft magnetic material used for the iron core material M When satisfy the following formula (1), it was found that the noise of the motor can be significantly reduced. Furthermore, S RT and S ST By satisfying the following formula (2) in addition to formula (1), it has been found that the motor torque can be significantly improved. The gist configuration of the present disclosure is as follows.

[0011] (1) The switched reluctance motor according to an embodiment of the present disclosure is A switched reluctance motor comprising a rotor having a plurality of salient poles without windings and a stator having salient poles with windings in a direction facing the salient poles of the rotor, The surface area S of the magnetic poles in the salient poles of the rotor RT and the surface area S of the magnetic poles in the salient poles of the stator ST The ratio of satisfies M 2.0×B with respect to the magnetic flux density B at which the soft magnetic material used for the iron core material exhibits the maximum magnetic permeability M ≦(S ST / S RT )≦3.5×B M .

[0012] (2) As an embodiment of the present disclosure, in (1), The magnetic flux density B M is 0.2 T to 0.9 T.

[0013] (3) As an embodiment of the present disclosure, in (1) or (2), The surface area S of the magnetic poles in the salient poles of the rotor RT and the surface area S of the magnetic poles in the salient poles of the stator ST The ratio of satisfies 1.55≦(S ST / S RT )≦2.55.

[0014] (4) As an embodiment of the present disclosure, in any one of (1) to (3), The soft magnetic material is an electromagnetic steel sheet having a plate thickness of 0.20 mm or less.

[0015] (5) As an embodiment of the present disclosure, in any one of (1) to (4), The soft magnetic material is an electromagnetic steel sheet having a Si concentration distribution in the plate thickness direction.

[0016] Here, in implementing the present disclosure, if the above configuration is satisfied, the components or manufacturing method of the soft magnetic material used are not limited. As the electromagnetic steel sheet having an Si concentration distribution in the plate thickness direction, for example, 10JNRF950B manufactured by JFE Steel can be used, but it is not limited thereto. When the soft magnetic material adopted is an electromagnetic steel sheet, it is desirable that the electromagnetic steel sheet has an insulating film with a thickness of 0.1 μm or more on at least one surface.

Advantages of the Invention

[0017] According to the present disclosure, a switched reluctance motor capable of achieving high torque characteristics and low noise can be provided.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0019] Hereinafter, a switched reluctance motor according to an embodiment of the present disclosure will be described with reference to the drawings. The switched reluctance motor according to this embodiment has, as described above, the surface area S of the magnetic poles at the poles of the rotor RT and the surface area S of the magnetic poles at the poles of the stator STIt is configured such that the ratio satisfies a predetermined formula. Here, the switched reluctance motor according to the present embodiment includes a rotor having a plurality of salient poles without windings, and a stator having salient poles with windings in a direction facing the salient poles of the rotor.

[0020] S, which is the surface area of the magnetic pole in the salient pole of the rotor RT is defined as the tip cross-sectional area × the number of salient poles. The tip cross-sectional area is calculated by multiplying the width of one salient pole by the stack thickness (see Fig. 5). Similarly, S ST which is the surface area of the magnetic pole in the salient pole of the stator is defined as the tip cross-sectional area × the number of salient poles. Here, B M is the magnetic flux density showing the maximum value (maximum permeability) in the permeability in the DC magnetization curve of the iron core material of the motor. In other words, B M is the value of the magnetic flux density at which the soft magnetic material used for the stator and rotor shows the maximum permeability. (S ST / S RT ) is designed according to B M so that the vibration and noise of the motor are suppressed. When (S ST / S RT ) is less than 2.0 × B M , the magnetic flux linked in the motor becomes too small with respect to the energization of the stator winding, leading to a decrease in motor torque. On the other hand, when (S ST / S RT ) exceeds 3.5 × B M , the efficiency of the motor decreases due to the influence of magnetic saturation of the rotor core during motor drive. Therefore, the switched reluctance motor may be designed such that (S ST / S RT ) satisfies the following formula (1).

[0021] 2.0 × B M ≦ (S ST / S RT ) ≦ 3.5 × B M … Formula (1)

[0022] Hereinafter, B MDetails thereof will be described. First, the magnetization characteristics of the soft magnetic material used for the motor core material are often evaluated using the magnetizing force H [A / m] and the magnetic flux density B [T] as they are. FIG. 1 illustrates the results of evaluating the magnetization curve using Epstein test pieces of 35A300 grade electromagnetic steel sheets specified by JIS according to JIS2550 (1992) for samples in the rolling direction and the direction perpendicular to rolling. On the other hand, in the method of the present disclosure, evaluation is performed using the permeability defined as the differential permeability obtained by “(dB / dH)×(1 / 4π)×10 -6 ”. Here, “×B M ” in Equation (1) has the meaning of corresponding the output and the magnetic flux density of the material so that a high magnetic flux density material is used for the switched reluctance motor with a large output. For example, in a switched reluctance motor with a large output, the difference between the number of rotor poles and the number of stator poles becomes large, and (S ST / S RT ) tends to become large. Also, to realize a switched reluctance motor with a large output, it is necessary to use a material with a high magnetic flux density. On the other hand, in a switched reluctance motor with a small output, a material with a low magnetic flux density can be used. By introducing an adjustment part that multiplies by B M , such an appropriate correspondence between the output and the magnetic flux density of the material can be included in Equation (1). Regarding (S ST / S RT ) in Equation (1), strictly speaking, it can be described as (S ST / S RT )×1 [T].

[0023] FIG. 2 shows the magnetization curve of FIG. 1 in terms of the relationship between the magnetic flux density and the permeability. In many soft magnetic materials, the permeability draws an upwardly convex curve with respect to the magnetic flux density B [T] and shows a behavior approaching a state where the permeability is 1 (vacuum). In FIG. 2, the magnetic flux density B M at which the permeability in the present disclosure shows the maximum value is shown. For the 35A300 grade electromagnetic steel sheet, B M was 0.56 T. FIG. 3 shows B 50 [T] and B M which are material evaluation indices in the magnetization curve of the conventional core material.Shows the relationship with [T]. B 50 and B M The correlation is weak, and it can be seen that B M is an entirely different material evaluation index. The method of the present disclosure can effectively reduce motor noise by controlling the surface area ratio of the magnetic poles at the salient poles of the rotor and stator of the switched reluctance motor using the evaluation index (B M ) of the iron core material that has not been conventionally considered.

[0024] Here, even if the magnetic poles at the tip of the salient poles of the rotor and stator have a non-uniform air gap structure, the effects of the present disclosure can be enjoyed.

[0025] In addition to satisfying the formula (1), by making the above surface area ratio (S ST / S RT ) satisfy the following formula (2), it becomes possible to increase the torque of the motor.

[0026] 1.55 ≦ (S ST / S RT ) ≦ 2.55... Formula (2)

[0027] In a switched reluctance motor, the magnetic flux generated by motor drive is only the field flux of the winding, and the magnetic flux emerging from the stator core and the magnetic flux passing through the rotor core and then returning to the stator core correspond one-to-one. Considering only this, it is expected that the efficiency is the best when the surface area ratio (S ST / S RT ) of the magnetic poles responsible for the transfer of magnetic flux becomes 1. However, in a high-output (high-torque) switched reluctance motor, by satisfying the formula (2), a distribution in which an inductance change occurs in a wide range in the rotational angle direction can be realized. Therefore, high torque of the motor is realized. Here, when (S ST / S RT ) is less than 1.55, large torque pulsations occur in the vicinity of the region where the magnetic poles face each other completely, and the motor noise increases. When (S ST / S RT) exceeds 2.55, it becomes impossible to secure the slot area for winding, resulting in a decrease in motor torque. Also, it is more preferable that 1.55 ≤ (S ST / S RT ) ≤ 1.8 is satisfied.

[0028] In a switched reluctance motor, using an electromagnetic steel sheet with a thin plate thickness and a Si concentration distribution (Si gradient) in the plate thickness direction is advantageous for improving the efficiency of the motor. The soft magnetic material used for the core material is preferably, for example, an electromagnetic steel sheet with a plate thickness of 0.20 mm or less and having a Si concentration distribution in the plate thickness direction. Here, the Si concentration distribution in the plate thickness direction can be evaluated by analyzing an embedded sample of the plate thickness cross-section with an EPMA (Electron Probe Micro Analyzer). If there is a difference of 0.5% or more in the average Si concentration with respect to the central layer (the layer between the front and back surfaces) on the front or back surface when the region is divided into three in the plate thickness direction, it can be determined that there is a Si concentration distribution in the plate thickness direction.

[0029] Also, the soft magnetic material used for the core material is preferably selected such that the magnetic flux density B M is 0.2 T to 0.9 T.

[0030] Hereinafter, the effects of the present disclosure will be specifically described based on examples, but the present disclosure is not limited to these examples.

[0031] (Examples) FIG. 4 is a diagram of a switched reluctance motor, showing the basic shapes of the stator and rotor (basic shapes). The switched reluctance motor in FIG. 4 has an 8 - 12 pole - pole structure with a stator outer diameter of 190 [mm] and a stacked thickness (stacked thickness) of 150 [mm]. That is, the number of poles on the rotor side is 8, and the number of poles on the stator side is 12. In the basic shape, the rotor outer diameter is 120 [mm].

[0032] FIG. 5 shows the surface areas of the magnetic poles (S ST and S RT) is a diagram showing. In the basic shape, the width of the salient pole on the stator side is 25 [mm], the width of the salient pole on the rotor side is 22 [mm], (S ST / S RT ) is 1.7. By changing the width of the salient pole, the torque and noise of the motor when (S ST / S RT ) is changed were evaluated. In the evaluation, the motor control condition was set to 4000 [rpm]. Also, the current condition was set to 40 [Arms] by hysteresis control. The motor noise was evaluated as the overall value [dB]. Also, the torque was evaluated as a normalized value. The evaluation results of the torque and noise of the motor are shown in Table 2. Here, various materials shown in Table 1 were used as the core material. The materials in Table 1 are indicated by the product names of electromagnetic steel sheets made by JFE Steel, and symbols are assigned to each of them. In Table 2, the material (core material) is indicated by the symbol in Table 1. Also, the DC B-H curve was obtained by the above Epstein test, and B M was evaluated. As shown in Table 2, the invention examples satisfy at least Equation (1). That is, those that do not satisfy Equation (1) are comparative examples.

[0033]

Table 1

[0034]

Table 2

[0035] Figure 6 shows the relationship between "(S ST / S RT ) / B M " and the motor noise based on the results shown in Table 2. As shown in Figure 6, the motor noise was reduced under the combination conditions of the motor structure and material that satisfy Equation (1). Also, Figure 7 shows (S ST / S RT) shows the relationship with the motor torque. As shown in Fig. 7, an improvement in the motor torque was recognized under the condition that both Equation (1) and Equation (2) are satisfied. Further analysis revealed that particularly high efficiency of the motor was recognized under the condition that the iron core material has a Si concentration distribution in the plate thickness direction.

[0036] As described in the embodiments, the switched reluctance motor according to this embodiment can achieve high torque characteristics and low noise (quietness) by controlling the ratio of the magnetic pole areas of the rotor and the stator according to the magnetic characteristics of the iron core material. By the method of the present disclosure, a switched reluctance motor with performance superior to the prior art can be realized without using magnets that use a large amount of rare earths, and it can contribute to the promotion of electrification in various fields including automobiles, so it has high industrial value.

[0037] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications or corrections based on the present disclosure. Therefore, it should be noted that these modifications or corrections are included in the scope of the present disclosure.

Claims

1. A switched reluctance motor comprising a rotor having a plurality of salient poles without windings, and a stator having salient poles with windings in a direction facing the salient poles of the rotor, The surface area S of the magnetic pole at the salient pole of the rotor ＲＴ and the surface area S of the magnetic pole at the salient pole of the stator ＳＴ The ratio of is such that the soft magnetic material used for the iron core material exhibits the maximum magnetic permeability at the magnetic flux density B Ｍ For, 2.0 × B Ｍ ≤ (S ＳＴ / S ＲＴ ) ≤ 3.5 × B Ｍ A switched reluctance motor that satisfies this condition.

2. The magnetic flux density B Ｍ The switched reluctance motor according to claim 1, wherein the magnetic flux density B is 0.2 T to 0.9 T.

3. The surface area S of the magnetic pole in the salient pole of the rotor ＲＴ and the surface area S of the magnetic pole in the salient pole of the stator ＳＴ has a ratio such that 1.55 ≤ (S ＳＴ / S ＲＴ ) ≤ 2.55, and the switched reluctance motor according to claim 1 or 2

4. The switched reluctance motor according to claim 1 or 2, wherein the soft magnetic material is an electromagnetic steel sheet having a thickness of 0.20 mm or less.

5. The switched reluctance motor according to claim 1 or 2, wherein the soft magnetic material is an electromagnetic steel sheet having a Si concentration distribution in the thickness direction.

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