JPH1169679A - Permanent magnet type motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce torque unevenness by forming a structure in which number of poles of a rotor and the number of the salient poles of a stator are specified, while forming a skew graded within the range of a specific electrical angle to the axis of rotation on a boundary between the unlike poles of a permanent magnet. SOLUTION: The number of poles of a rotor 7 is desirably 4 and the number of the salient poles of a stator 1 is desirably 6, and permanent magnets 9 are formed in magnetizing structure, in which skews graded at a specified electrical angle to the axis of rotation are formed on boundary lines among N poles and S poles. In torque unevenness under the energization of an armature, a skew angle, where the square root of the square sum of the quinary high- harmonic component and septimal high-harmonic component of a air-gap magnetic flux density is reduced, regarding these high-harmonic components may be selected. The skew angle (the electric angle) of 60-80 deg is set desirably as the result of calculation. Accordingly, torque unevenness under the energization of an armature coil can be lowered optimally.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a permanent magnet type motor having a skew suitable for reducing torque unevenness when an armature coil is energized.

[0002]

2. Description of the Related Art As is well known, in a permanent magnet type motor, particularly a motor having a salient pole structure, a relative geometrical relationship between an armature core having salient poles and a permanent magnet as a field portion. The reluctance changes depending on the positional relationship, and the force acting on each part of the magnetic pole is not symmetric with respect to the rotation axis, so that a so-called cogging torque is generated, which causes torque unevenness and vibration.

As one method of reducing such cogging torque, a skew has been conventionally provided at the boundary between different poles of the rotor permanent magnet, and the geometrical positional relationship between the salient poles and the permanent magnet has been changed in the axial direction. On the other hand, averaging is performed.
For example, as shown in JP-A-1-8853,
In a brushless motor in which the number of salient poles of the stator field iron core is 1.5 times the number of poles of the rotor permanent magnet, an angle corresponding to 1/2 of a slot interval forming salient poles of the stator field iron core is used. Skew is provided on the rotor permanent magnet. This focuses on the fact that a peak corresponding to twice the number of salient poles of the stator field iron core appears in the measured waveform of the cogging torque.

Japanese Patent Application Laid-Open No. 2-74136 discloses a permanent magnet type motor having a rotor having four magnetic poles and a stator having six salient poles. The means for providing a skew of 45 [deg] is shown. This focuses on balancing the magnetic flux distribution state in which the rotational force acts and the magnetic flux distribution state in which the fixing force acts.

[0005]

By the way, torque unevenness generated when a permanent magnet type motor is driven includes torque unevenness when an armature coil is energized, in addition to the cogging torque described above. In the drive state in which a three-phase sine wave current is applied to the armature winding (armature coil) with the three-phase Y connection, the permanent magnet which is the field part is formed. The air gap magnetic flux density does not form a sine wave distribution in the circumferential direction, and as a result, the air gap magnetic flux density has a higher harmonic component, particularly, the fifth and seventh harmonic components. In other words, in a permanent magnet type motor, the mutual relationship between the rotating magnetic field generated by passing a multi-phase alternating current through the armature winding wound on the stator and the field of the permanent magnet disposed on the rotor is generated. Since a torque is generated by an attractive force or a repulsive force as an action, if a harmonic component is present in the air gap magnetic flux density created by the permanent magnet, torque unevenness corresponding to the harmonic component is generated. In this case, a torque corresponding to the third n-th harmonic component (n is an integer of 1 or more) of the air gap magnetic flux density is not generated because the interaction with the rotating magnetic field due to the three-phase armature current cancels out.

As a means for making the air gap magnetic flux density created by the permanent magnet closer to a sine wave in response to such torque unevenness when the armature coil is energized, conventionally, the thickness of the permanent magnet in the radial direction is sequentially changed in the circumferential direction. Such methods have been used. However, processing the permanent magnet with high accuracy in the thickness direction has a problem in terms of productivity. In addition, if the above-described skew is provided to the permanent magnet for the purpose of reducing the cogging torque, not only the cogging torque but also the torque unevenness when the armature coil is energized can be reduced to some extent. In the skew, the torque unevenness when the armature coil is energized has not been considered in the design.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a permanent magnet motor having an optimum skew for reducing torque unevenness when an armature coil is energized. is there.

[0008]

In order to achieve the above object, a permanent magnet type motor according to the present invention comprises a plurality of salient poles arranged in a circumferential direction, wherein a three-phase armature winding is wound by concentrated winding. Radial motor comprising a stator having permanent magnets and permanent magnets arranged such that different poles are alternately adjacent to each other in the circumferential direction, wherein n is an integer of 1 or more. The number of magnetic poles is 2n, the number of salient poles of the stator is 3n, and an electric angle of 60 [deg] to 80 [deg] with respect to a rotation axis at a boundary between different poles of the permanent magnet. A skew inclined in the inside is provided.

According to the present invention, the fifth and seventh harmonic components among the harmonic components of the air gap magnetic flux density created by the permanent magnet are provided.
Since the square root of the sum of squares of the next harmonic component can be minimized and the decrease in the generated torque is small, torque unevenness when the armature coil is energized can be efficiently and optimally reduced.

[0010]

FIG. 1 shows a first embodiment of the present invention.
7 will be described with reference to FIG. FIG. 2 shows a cross section perpendicular to the axis of the permanent magnet type motor. The stator 1, which is located on the inner peripheral side of the permanent magnet type motor and is attached to a stationary part (not shown), has an armature core 2 provided with six equal-width salient poles 3 at equal intervals, and concentrated on the salient poles 3. And an armature winding (armature coil) 4 which is wound by winding and forms a three-phase Y connection. A rotating shaft 6 is inserted into and supported by a stationary portion (not shown) via a bearing 5, and a rotor 7 is connected to the rotating shaft 6 so as to surround the armature core 2.

The rotor 7 has a cylindrical rotor yoke 8
And a permanent magnet 9 attached to the inner peripheral surface of the rotor yoke 8. The permanent magnet 9 has two N-poles and two S-poles (the number of magnetic poles: 4) magnetized at equal widths so that different poles are alternately arranged in the circumferential direction. And a gap 10 between the inner peripheral surface thereof and the salient pole 3. In this case, since the number of magnetic poles of the rotor 7 is 4 and the number of salient poles of the stator 1 is 6,
The ratio is 2: 3. Further, referring to FIG. 1, which shows the circumferential development of the permanent magnet 9, the boundary between the N pole and the S pole of the permanent magnet 9 is defined with respect to the rotation axis (the axis direction is referred to as the axial direction). Electric angle 70 [de
g], and has a magnetized structure provided with a skew inclined to indicate the angle a.

The permanent magnet type motor having the above configuration is driven by, for example, an inverter circuit shown in FIG. In FIG. 3, switching elements 14 to 1 such as transistors, for example, are provided between a positive DC power supply line 12 and a negative DC power supply line 13 connected to a positive terminal and a negative terminal of a DC power supply 11.
9 is connected in a three-phase bridge connection. Reflux diodes 20 to 25 are connected in parallel to these switching elements 14 to 19, respectively.
31 is connected via base resistors 32-37.
These base drive circuits 26 to 31 are connected to a drive control circuit including a position detection unit (not shown), a speed control unit, a conduction control unit, and the like. The output lines 39u, 39v, 39w of the switching means 38 are connected to the three-phase Y-connected armature windings 41 of the permanent magnet type motor 40.
u, 41v, and 41w are connected. These 41u,
41v and 41w constitute the armature winding 4 shown in FIG.

It is an object of the present invention to set an optimum skew angle for reducing torque unevenness when a permanent magnet type motor is energized with an armature coil. It is necessary to take this into consideration except for the case where the daughter current itself is distorted. Therefore, hereinafter, a case will be described in which a three-phase sine-wave current is supplied to a three-phase Y-connected armature winding using the inverter circuit to drive the armature winding.

In the following, the skew angle is set to an electrical angle of 70 [d
[eg] will be described in detail with reference to FIGS. First, when n is an integer of 1 or more, the number of magnetic poles of the rotor is 2n and the number of salient poles of the stator is 3 as shown in FIG.
A motor model having a skew angle of 0 [deg] is set for a permanent magnet motor having a 2: 3 structure in which n is used and a rare-earth permanent magnet. Then, a magnetic field analysis is performed on the motor model using the finite element method to determine an air gap magnetic flux density. Further, when a frequency analysis is performed on the air gap magnetic flux density to calculate each harmonic component of the air gap magnetic flux density, the results shown in the following table are obtained. As shown in the table, there is no even-order harmonic component, and the description of the 31st or higher harmonic component is omitted.

[0015]

[Table 1]

Next, the skew angle 0 [de] shown in Table 1 above
g], the respective harmonic components of the air gap magnetic flux density when a skew is provided are calculated based on the harmonic components obtained.
In this calculation, it is assumed that the phase of each higher harmonic component of the air gap magnetic flux density at each axial position is sequentially shifted by an angle corresponding to the circumferential displacement of the magnetic pole due to skew. Not considered.

Assuming that the m-th harmonic component of the air gap magnetic flux density at a skew angle of 0 [deg] is S0 (m), the air gap magnetic flux at a skew angle of 0 [deg] at an axial position z and an angular position θ. The density b (0, z, θ) is as shown in Equation 1.

[0018]

(Equation 1)

On the other hand, the skew angle (mechanical angle) a [d
When the displacement angle (electrical angle) due to skew at the axial position z is x [rad], the air gap magnetic flux density b (a, z) at the axial position z and the angular position θ is provided. ,
θ) is as shown in Expression 2. Note that the displacement angle (electric angle) due to skew is the dimension in which the magnetic pole is displaced in the circumferential direction due to skew, expressed as an electric angle.

[0020]

(Equation 2)

In this case, the relationship between the displacement angle (electrical angle) x [rad] due to skew at the axial position z and the skew angle (mechanical angle) a [deg] is shown in FIGS.
This will be described with reference to FIG. FIG. 4 is a perspective view of the permanent magnet, and FIG. 5 is a development view of one pole pair in the circumferential direction of the permanent magnet. An annular permanent magnet having two north poles and two south poles has an inner radius r, an effective axial dimension L, and a skew angle (mechanical angle) a [deg] between different poles.
Is provided. The circumferential angle of one pole pair shown in FIG. 5 is 2π [rad] in electrical angle, and its length is represented by 2πr · (2 / P) where P is the number of magnetic poles. Therefore,
Skew displacement angle (electric angle) x at axial position z
[Rad] and its length dimension X, X = x · (2
r / P) holds. If this relationship is applied to tan (a) = X / z, which is an expression for the skew angle, the following expression 3 is obtained.

[0022]

(Equation 3)

The average value B of the m-th harmonic component of the air gap magnetic flux density averaged in the axial direction by providing the skew
m (ψ, θ) may be obtained by integrating and averaging Equation 2 with respect to the axial position z, and calculating the total displacement angle (electric angle) due to skew at the effective axial dimension position L of the permanent magnet as ψ [ra
d], the relationship can be derived as shown in Expression 4 by applying the relationship of x = ψ · (z / L) to Expression 2.

[0024]

(Equation 4)

FIG. 6 shows the m-th harmonic component (average value) Bm of the air gap magnetic flux density derived as described above.
The relationship between (の, θ) and the skew angle is shown. In FIG. 6, the vertical axis represents the harmonic component of the air gap magnetic flux density, and the horizontal axis represents the skew angle (electric angle) [deg]. FIG. 6 shows five lines indicated by, which are, in order, the fundamental component, the third harmonic component, the fifth harmonic component, and the seventh harmonic component of the air gap magnetic flux density. And the square root of the sum of squares of the fifth harmonic component and the seventh harmonic component. The magnetic flux density value on the left vertical axis is applied from here on, and the magnetic flux density value on the right vertical axis is applied.

As described above, if the torque unevenness when the armature coil is energized is not affected by the third n-th harmonic component of the air gap magnetic flux density and the eleventh or higher harmonic component is sufficiently small, After all, the skew angle at which the square root of the sum of the squares of the fifth harmonic component and the seventh harmonic component of the air gap magnetic flux density becomes small may be selected. In FIG. 6, the square root of the sum of squares of the fifth harmonic component and the seventh harmonic component is the minimum when the skew angle (electrical angle) is about 145 to 1
This is at the time of 50 [deg]. However, if the skew angle is increased, the fundamental wave component that generates torque also decreases, and the generated torque decreases by nearly 30% at the skew angle of 145 to 150 [deg], which is not appropriate. Therefore, a skew angle (electric angle) of 60 [deg] to 80 [deg], particularly 70 [deg], at which the square root of the sum of squares of the fifth harmonic component and the seventh harmonic component is minimized, is set. I do. The harmonic components of the air gap magnetic flux density at the skew angle (electric angle) of 70 [deg] are shown in the table below, and the magnetic flux density distribution is shown in FIG. 7 for reference. In this case, the skew angle is 0
Compared to the case of [deg], the generated torque can output about 94%, and the second harmonic of the fifth harmonic component and the seventh harmonic component can be output.
Since the square root of the sum of squares is reduced to about 1/10, it is possible to optimally reduce torque unevenness when the armature coil is energized.

[0027]

[Table 2]

Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 8 is a development view of the rotor permanent magnet 9 in the circumferential direction. The easily processed permanent magnet 9 formed of magnetic powder has electrical angles with respect to the rotation axis at the boundary between the N pole and the S pole. Two skews inclined at an angle of 60 [deg] and 80 [deg] are provided, and a region sandwiched between these two skews is a non-magnetized region D to form a magnetized structure.

FIG. 9 shows a skew angle as a parameter.
This graph shows the circumferential distribution of the square root of the sum of squares of the fifth harmonic component and the seventh harmonic component of the air gap magnetic flux density. The vertical axis represents the magnetic flux density, and the horizontal axis represents the circumferential position (electrical angle). ). The lines indicated by are thin solid lines, respectively.
[Deg] single skew, dash-dot line is 65 [de]
g] and skew of 75 [deg], and the thick solid line is 60 [d].
eg] and skew of 80 [deg], and the broken line is 55 [d].
[deg] and 85 [deg] skew. The designated position with respect to each line represents a point where the magnetic flux density has the maximum value. These maximum values are in the order from 0.010291 [T], 0.00
9441 [T], 0.008325 [T], and 0.
01067 [T], 60 [deg] and 80 [de]
g] when the skew is provided. The harmonic component of the air gap magnetic flux density in this case is shown in the table below, and the magnetic flux density distribution is shown in FIG. 10 for reference. At this time, the square root of the sum of squares of the fifth harmonic component and the seventh harmonic component is further reduced without reducing the generated torque as compared with the first embodiment using a single skew of 70 [deg]. Since it is reduced by about 20%, the torque unevenness when the armature coil is energized can also be reduced by about 20%.

[0030]

[Table 3]

As described above, in this embodiment,
The current motor model (4 magnetic poles, 6 salient poles) without skew is used to optimally reduce the uneven torque due to the harmonic components of the air gap magnetic flux density while energizing the armature coil by providing skew. Magnetic field analysis and frequency analysis were performed on the air gap magnetic flux density, and based on the obtained air gap magnetic flux density, the air gap magnetic flux density when a skew was provided was calculated by a theoretical formula. As a result, the square root of the sum of squares of the fifth harmonic component and the seventh harmonic component of the air gap magnetic flux density, which is a main factor of torque unevenness when the armature coil is energized, is minimized, and the generated torque is reduced. A small skew angle (electrical angle) of 60 [deg] to 80 [deg], particularly 70 [deg]
[Deg] was found to be optimal. Then, two skews inclined at angles of 60 [deg] and 80 [deg] (electrical angle) are provided, and a region sandwiched between these two skews is defined as a non-magnetized region. If this is the case, it is possible to further reduce torque unevenness when the armature coil is energized by about 20%.

The present invention is not limited to the embodiment described above and shown in the drawings, but can be extended or modified as follows. Generally, in order to reduce the cogging torque, the third harmonic component of the air gap magnetic flux density becomes zero.
A skew angle (electric angle) of [deg] (see FIG. 6) or a skew angle (electric angle) of 90 [deg] that is close to 0 including other harmonic components is provided. In such a conventional skew setting for the purpose of reducing the cogging torque, according to FIG. 6 derived in the present embodiment, 60 [deg] to 90 [de] are set.
g], or a skew angle (electrical angle) of 120 [deg] to 180 [deg], it is possible to greatly reduce torque unevenness when the armature coil is energized.

[0033]

According to the first aspect of the present invention, in a permanent magnet type motor having a ratio of the number of magnetic poles to the number of salient poles of 2: 3, the fifth and seventh harmonic components of the air gap magnetic flux density are reduced. Since the square root of the sum of squares is very small and the generated torque is reduced by a small amount, it is possible to efficiently reduce torque unevenness when the armature coil is energized. In this case, not only the torque unevenness when the armature coil is energized but also the cogging torque can be reduced.

According to the second aspect of the present invention, the air gap magnetic flux density of the fifth
The square root of the sum of squares of the seventh harmonic component and the seventh harmonic component is minimized, and the torque unevenness when the armature coil is energized can be reduced to about 1/10 as compared with the case where no skew is provided. Further, the decrease in the generated torque due to the skew can be suppressed to about 6%.

According to the third and fourth aspects of the present invention, since two skews having different angles are provided, the torque unevenness when energizing the armature coil is further reduced by about 20% as compared with the case where one skew is provided. Can be reduced. In this case as well, not only the torque unevenness when the armature coil is energized but also the cogging torque can be reduced.

[Brief description of the drawings]

FIG. 1 is a development view of a permanent magnet showing a first embodiment of the present invention.

FIG. 2 is a cross-sectional view perpendicular to the axis of a permanent magnet type motor.

FIG. 3 is a configuration diagram of a permanent magnet type motor drive circuit.

FIG. 4 is a perspective view of a permanent magnet of a motor model.

FIG. 5 is a development view of the permanent magnet of FIG. 4;

FIG. 6 is a diagram illustrating a relationship between a skew angle and a harmonic component.

FIG. 7 is a distribution diagram of air gap magnetic flux density at a skew angle of 70 [deg].

FIG. 8 is a view corresponding to FIG. 1 showing a second embodiment of the present invention.

FIG. 9 is a circumferential distribution diagram of the square root of the sum of squares of the fifth harmonic component and the seventh harmonic component of the air gap magnetic flux density.

FIG. 10 shows skew angles of 60 [deg] and 80 [deg].
Of magnetic flux density distribution in air

[Explanation of symbols]

In the figure, 1 is a stator, 3 is a salient pole, 4 is an armature winding (armature coil), 7 is a rotor, 9 is a permanent magnet, 11 is a DC power supply, 14 to 19 are switching elements, and 38 is switching. The means 40 is a permanent magnet type motor.

Claims (4)

[Claims] 1. A stator in which three-phase armature windings are wound by concentrated winding around a plurality of salient poles arranged in the circumferential direction, and permanent magnets are alternately arranged in the circumferential direction so that different poles are adjacent to each other. A radial motor comprising: a rotor provided with a rotor having a magnetic pole number of 2n and a stator having a salient pole number of 3n, where n is an integer of 1 or more. An electrical angle of 60 with respect to the axis of rotation at the boundary between the different poles of the permanent magnet.
A permanent magnet type motor provided with a skew inclined in a range of [deg] to 80 [deg]. 2. An inclination angle of a skew is an electrical angle of 70 [de].
g]. 3. A stator in which a three-phase armature winding is wound around a plurality of salient poles arranged in the circumferential direction by concentrated winding, and permanent magnets are arranged so that different poles are alternately adjacent to each other in the circumferential direction. A radial motor comprising: a rotor provided with a rotor having a magnetic pole number of 2n and a stator having a salient pole number of 3n, where n is an integer of 1 or more. The electrical angle of 6 at the boundary between the different poles of the permanent magnet with respect to the axis of rotation.
A permanent magnet type motor characterized in that two skews inclined in a range of 0 [deg] to 80 [deg] are provided, and a region sandwiched between these two skews is a non-magnetized region. 4. The inclination angle of each of the two skews is 6 electrical degrees.
The permanent magnet type motor according to claim 3, wherein the angle is 0 [deg] and the electric angle is 80 [deg].