WO2022113181A1 - 永久磁石同期モータ - Google Patents
永久磁石同期モータ Download PDFInfo
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- WO2022113181A1 WO2022113181A1 PCT/JP2020/043729 JP2020043729W WO2022113181A1 WO 2022113181 A1 WO2022113181 A1 WO 2022113181A1 JP 2020043729 W JP2020043729 W JP 2020043729W WO 2022113181 A1 WO2022113181 A1 WO 2022113181A1
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- WIPO (PCT)
- Prior art keywords
- permanent magnet
- synchronous motor
- magnet synchronous
- recess
- protrusions
- Prior art date
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- 230000001360 synchronised effect Effects 0.000 title claims description 83
- 230000004907 flux Effects 0.000 claims description 14
- 230000005855 radiation Effects 0.000 claims description 8
- 239000000696 magnetic material Substances 0.000 claims description 2
- 230000007704 transition Effects 0.000 abstract 1
- 230000005347 demagnetization Effects 0.000 description 35
- 230000007423 decrease Effects 0.000 description 20
- 230000000694 effects Effects 0.000 description 14
- 230000004048 modification Effects 0.000 description 13
- 238000012986 modification Methods 0.000 description 13
- 230000002427 irreversible effect Effects 0.000 description 6
- 230000009467 reduction Effects 0.000 description 6
- 230000003313 weakening effect Effects 0.000 description 6
- 238000010586 diagram Methods 0.000 description 5
- 238000000034 method Methods 0.000 description 4
- 230000006866 deterioration Effects 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 229910001172 neodymium magnet Inorganic materials 0.000 description 3
- 230000008859 change Effects 0.000 description 2
- 230000002093 peripheral effect Effects 0.000 description 2
- 239000011800 void material Substances 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K1/00—Details of the magnetic circuit
- H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
- H02K1/22—Rotating parts of the magnetic circuit
- H02K1/27—Rotor cores with permanent magnets
- H02K1/2706—Inner rotors
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K1/00—Details of the magnetic circuit
- H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
- H02K1/22—Rotating parts of the magnetic circuit
- H02K1/27—Rotor cores with permanent magnets
- H02K1/2706—Inner rotors
- H02K1/272—Inner rotors the magnetisation axis of the magnets being perpendicular to the rotor axis
- H02K1/274—Inner rotors the magnetisation axis of the magnets being perpendicular to the rotor axis the rotor consisting of two or more circumferentially positioned magnets
- H02K1/2753—Inner rotors the magnetisation axis of the magnets being perpendicular to the rotor axis the rotor consisting of two or more circumferentially positioned magnets the rotor consisting of magnets or groups of magnets arranged with alternating polarity
- H02K1/278—Surface mounted magnets; Inset magnets
- H02K1/2781—Magnets shaped to vary the mechanical air gap between the magnets and the stator
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/64—Electric machine technologies in electromobility
Definitions
- This application relates to a permanent magnet synchronous motor.
- the following prior art documents are available as a technique for increasing the d-axis inductance Ld and performing effective weakening magnetic flux control with a small d-axis current Id.
- the d-axis inductance Ld is increased and weakened by forming protrusions protruding in the radial direction from the rotor core so as to fit into a plurality of permanent magnets arranged on the surface of the rotor core, and the field control is effectively functioned to achieve high rotation.
- the torque output at the time is improved.
- a concave portion is provided in the central portion of the permanent magnet, and the protrusion that fits in this portion protrudes from the rotor core. Since the concave portion of the permanent magnet has a rectangular shape, the outer diameter of the permanent magnet is an arc, so that the corner portion of the concave portion has a thin magnet thickness.
- permanent magnets such as Nd—Fe—B-based neodymium magnets, undergo irreversible demagnetization in which the residual magnetic flux density decreases when exposed to a demagnetizing field from a stator or a high temperature environment.
- the thickness of the concave corner portion and the arc of the outer diameter of the magnet becomes thin, irreversible demagnetization is easy, and the torque output is lowered.
- This application has been made to solve the above-mentioned problems, and it is possible to suppress the deterioration of torque characteristics due to irreversible demagnetization, and it is also possible to improve the torque output at high rotation and high speed.
- the purpose is to obtain a permanent magnet synchronous motor.
- the permanent magnet synchronous motor disclosed in the present application is a rotor having a rotor core made of a magnetic material and a plurality of permanent magnets attached to the surface of the rotor core. Alternatively, it has a plurality of protrusions, and the permanent magnet has one or a plurality of recesses so that the protrusions fit, and the shortest distance between the outermost part of the recess and the outer diameter arc portion of the permanent magnet is set.
- L1 the outermost tangent of the permanent magnet recess and the parallel line parallel to the radiation from the center of the rotor shaft toward the center of the permanent magnet as the starting point for switching from the attachment surface of the permanent magnet and the rotor core to the recess.
- the recess has a recess where L2 ⁇ L1.
- the permanent magnet synchronous motor of the present application it is possible to suppress the deterioration of the torque characteristics, and it is also possible to improve the torque output at high rotation speed and high speed.
- FIG. FIG. 5 is an enlarged cross-sectional view of the vicinity of the permanent magnet in the cross section on the plane perpendicular to the shaft of the permanent magnet synchronous motor according to the first embodiment.
- FIG. 5 is an enlarged cross-sectional view of the vicinity of the permanent magnet in the cross section on the plane perpendicular to the shaft of the permanent magnet synchronous motor of the prior art, which is a contrast with the first embodiment. It is a figure which compared the speed-torque characteristic by the presence or absence of a protrusion / recess of a permanent magnet synchronous motor.
- FIG. 5 is an enlarged cross-sectional view of the vicinity of the permanent magnet in the cross section on the plane perpendicular to the shaft of the permanent magnet synchronous motor according to the second embodiment. It is a figure which compared the demagnetization rate distribution of the permanent magnet synchronous motor which concerns on Embodiment 2 and the permanent magnet synchronous motor which becomes the contrast. It is a figure which compared the induced voltage before demagnetization of the permanent magnet synchronous motor which concerns on Embodiment 2 and the permanent magnet synchronous motor which becomes the contrast. It is a figure which compared the induced voltage decrease rate after demagnetization of the permanent magnet synchronous motor which concerns on Embodiment 2 and the permanent magnet synchronous motor which becomes the contrast.
- FIG. 1 It is a partially enlarged sectional view which showed the modification 1 of the permanent magnet synchronous motor which concerns on Embodiment 2.
- FIG. 2 is a partially enlarged sectional view which showed the modification 2 of the permanent magnet synchronous motor which concerns on Embodiment 2.
- FIG. 2 is a partially enlarged view which showed the modification 3 of the permanent magnet synchronous motor which concerns on Embodiment 2.
- FIG. 4 is a partially enlarged view which showed the modification 4 of the permanent magnet synchronous motor which concerns on Embodiment 2.
- FIG. 5 is an enlarged cross-sectional view of the vicinity of the permanent magnet in the cross section on the plane perpendicular to the shaft of the permanent magnet synchronous motor according to the third embodiment. It is a figure which compared the demagnetization rate distribution of the permanent magnet synchronous motor which concerns on Embodiment 3 and the permanent magnet synchronous motor which becomes the contrast. It is a figure which compared the induced voltage before demagnetization of the permanent magnet synchronous motor which concerns on Embodiment 3 and the permanent magnet synchronous motor which becomes the contrast. It is a figure which compared the induced voltage decrease rate after demagnetization of the permanent magnet synchronous motor which concerns on Embodiment 3 and the permanent magnet synchronous motor which becomes the contrast.
- FIG. 1 It is a partially enlarged sectional view which showed the modification 1 of the permanent magnet synchronous motor which concerns on Embodiment 3.
- FIG. 2 It is a partially enlarged sectional view which showed the modification 2 of the permanent magnet synchronous motor which concerns on Embodiment 3.
- FIG. It is a partially enlarged sectional view which showed the modification 3 of the permanent magnet synchronous motor which concerns on Embodiment 3.
- FIG. It is a partially enlarged sectional view which showed the modification 4 of the permanent magnet synchronous motor which concerns on Embodiment 3.
- FIG. It is a partially enlarged sectional view which showed the modification 5 of the permanent magnet synchronous motor which concerns on Embodiment 3.
- FIG. 1 It is a partially enlarged sectional view which showed the modification 2 of the permanent magnet synchronous motor which concerns on Embodiment 3.
- FIG. It is a partially enlarged sectional view which showed the
- FIG. 1 It is sectional drawing which showed the other example of the rotor in the permanent magnet synchronous motor which concerns on Embodiment 4.
- FIG. 2 It is sectional drawing which showed the other example of the rotor in the permanent magnet synchronous motor which concerns on Embodiment 4.
- FIG. 1 It is sectional drawing which showed the other example of the rotor in the permanent magnet synchronous motor which concerns on Embodiment 4.
- FIG. 1 is a cross-sectional view showing a configuration in which the permanent magnet synchronous motor 100 according to the present embodiment is cut perpendicular to the axial direction.
- the direction along the axis of the rotor 20 in the permanent magnet synchronous motor 100 is defined as the axial direction.
- the direction along the radius of the rotor 20 is defined as the radial direction.
- the direction along the rotation direction of the rotor 20, that is, the direction along the circumference about the axis of the rotor 20 in the above cross section is defined as the circumferential direction.
- the permanent magnet synchronous motor 100 has a stator 10 and a rotor 20 rotatably provided with respect to the stator 10.
- the stator 10 is provided so as to surround the outer periphery of the rotor 20 via a gap 15 that serves as a magnetic gap.
- the stator 10 has a stator core 11 and a plurality of coils 14.
- the stator core 11 has a core back 12 formed on an annulus, and a plurality of teeth 13 protruding from the core back 12 toward the inner peripheral side.
- the plurality of coils 14 are wound around the plurality of teeth 13, respectively.
- 12 teeth 13 and 12 coils 14 are provided.
- the core back 12 is configured by connecting a plurality of core blocks each formed on an arc on an annulus, but the core back 12 may be integrally formed. Further, the core back 12 and each tooth 13 may be formed separately.
- the rotor 20 is a surface-side magnet type motor (SPM) in which a rotor core 21 and a plurality of permanent magnets 22 are arranged in the circumferential direction on the surface of the rotor core 21.
- the permanent magnets 22 are arranged so that the magnetizing directions are different so that if one of the permanent magnets 22 adjacent in the circumferential direction has an N pole on the outer diameter side, the other has an S pole. That is, the permanent magnets are arranged so that the polarities of the surfaces of the adjacent permanent magnets facing the stator are different.
- FIG. 1 is a so-called permanent magnet synchronous motor having 8 poles and 12 slots, in which the number of teeth 13 and the number of coils 14 is 12 and the number of permanent magnets 22 is 8.
- the combination of the numbers of the teeth 13 and the coils 14 is not limited to this. Further, although the number of teeth 13 and the number of coils 14 are the same, they may be different.
- the rotor core 21 has, for example, a configuration in which a plurality of core plates are laminated in the axial direction.
- the rotor core 21 has a shaft 23 penetrating in the axial direction.
- the rotor core 21 has a protrusion 24 protruding in the radial direction, and the permanent magnet 22 has a recess 25 into which the protrusion 24 fits.
- the protrusion 24 and the recess 25 will be described in detail with reference to FIG.
- FIG. 2 is an enlarged view of a portion surrounded by the broken line circle E in FIG.
- a radiation RL extending radially from the center of the axis toward the center of the permanent magnet 22 is defined.
- the surface where the rotor core 21 and the permanent magnet 22 are in contact with each other is designated as the sticking surface AS, the point where the sticking surface AS and the concave portion 25 change is set as the starting point SP, and the line parallel to the radiation RL is referred to as the parallel line PL.
- a line in contact with the outermost portion of the recess 25 and perpendicular to the radiation RL is referred to as a tangent line TL.
- the point where the tangent line TL and the parallel line PL intersect is defined as the intersection point A.
- the concave portion 25 has a shape such that L1 ⁇ L2, and in FIGS. 1 and 2, the concave portion corner portion has an arc shape.
- FIG. 3 is a cross-sectional view showing a configuration in which a conventional permanent magnet synchronous motor for comparison with the permanent magnet synchronous motor 100 according to the first embodiment is cut perpendicular to the axial direction.
- the stator is not shown.
- FIG. 3 it is assumed that the configuration without explanation is the same as that in FIG.
- the protrusion 240 of the rotor core 21 and the recess 250 of the permanent magnet 22 have a rectangular shape, and the relationship is L1> L2.
- the permanent magnet synchronous motor cannot output the torque T by generating a terminal voltage Vt that exceeds the motor input voltage Vi.
- Vt ⁇ (Vd 2 + Vq 2 ) ...
- Vd RId + ⁇ LqIq ...
- Vq RIq + ⁇ m + ⁇ LdId ...
- Vd and Vq are dq-axis voltage
- R is phase resistance
- Id and Iq are dq-axis current
- ⁇ m magnet magnetic flux
- Ld and Lq are dq-axis inductance
- ⁇ is angular velocity
- f is frequency
- N is per minute.
- the number of revolutions and pn of are pole pairs.
- weakening magnetic flux control that suppresses an increase in terminal voltage.
- This weakening magnetic flux control is a control method in which the d-axis current Id is energized in the direction of weakening the magnet magnetic flux ⁇ m, but when the d-axis inductance Ld is small, it is necessary to flow a large d-axis current Id.
- Iinv the current supplied from the inverter to the motor
- the torque T output by the SPM type permanent magnet synchronous motor is generally as shown in the following equation (6).
- T Pn ⁇ mIq ... (6) Therefore, when the d-axis current Id increases, the q-axis current Iq for outputting the torque T decreases, and the torque output decreases. Therefore, in order to increase the torque T at high rotation, it is necessary to effectively obtain the weakening magnetic flux control with a small d-axis current Id, and it is necessary to increase the d-axis inductance Ld. Therefore, the d-axis inductance Ld can be improved by adopting the structure shown in FIG. In FIG.
- the horizontal axis is the speed (rotational speed), and the vertical axis is the torque output, which is called a speed-torque characteristic. As shown in FIG. 4, it can be seen that the torque output at a high rotation speed (high speed) is increased by applying the protrusion 24 and the recess 25.
- the permanent magnet has a phenomenon called irreversible demagnetization in which the residual magnetic flux density Br of the permanent magnet decreases due to the temperature rise of the permanent magnet or the demagnetizing field in which a magnetic field is applied from the stator in the direction opposite to the magnetizing direction.
- the ease of this irreversible demagnetization is related to the coercive force of the permanent magnet and the permeance coefficient Pc determined by the magnetic circuit.
- the permeance coefficient Pc depends on the magnetizing direction thickness and the magnetoresistance of the magnet.
- the permit coefficient Pc is as follows when the magnetic gap between the stator and the rotor is Hm and the magnetic gap between the stator and the rotor is gm in a magnetic circuit such as a permanent magnet synchronous motor where the magnetic gap between the stator and the rotor is narrow. It can be approximated by the equation (7). Pc ⁇ Hm / gm ... (7)
- FIG. 5 shows the result of calculating the demagnetized state of the permanent magnet 22 by magnetic field analysis.
- 5 (a) shows L1> L2
- FIG. 5 (c) shows the demagnetization rate distribution in the case of L1 ⁇ L2.
- the dark part indicates that the demagnetization rate is high, and the light part indicates that the demagnetization rate is low.
- the recess 25 of the permanent magnet 22 has an arc shape so that the shortest distance L2 between the outer diameter of the permanent magnet 22 and the recess 25 is L1 ⁇ L2.
- FIG. 5 shows the induced voltage reduction rate before and after demagnetization in the shape shown in FIG. 5, and is standardized with the induced voltage reduction rate of L1> L2 being 1.0.
- the rate of decrease in the induced voltage is smaller than that of the prior art L1> L2.
- it leads to a decrease in the induced voltage that is, a decrease in the magnet magnetic flux ⁇ m, which is nothing but a decrease in the torque T described above, and a decrease in torque in the low speed range.
- the speed-torque characteristic shown in FIG. 4 does not change, and the effect of improving the output can be similarly obtained.
- FIG. 7 is a partially enlarged view of the modified form 1 of the permanent magnet synchronous motor according to the first embodiment.
- the only difference between FIGS. 1 and 7 is that the outermost shape of the concave portion 25 of the permanent magnet 22 is an arc or is flat and has rounded corners. , There is no difference in the obtained effect.
- FIG. 8 is also a partially enlarged view of the modified form 2 of the permanent magnet synchronous motor according to the first embodiment.
- FIG. 8 is different from FIGS. 1 and 7 in that the corner portion of the recess 25 of the permanent magnet 22 is formed diagonally, but the effect obtained in this shape is also different from the structure shown in FIG. There is no.
- the surfaces of the protrusion 24 of the rotor core 21 and the recess 25 of the permanent magnet 22 shown in the first embodiment are in contact with each other, all the surfaces may not be in contact with each other, and only one surface is in contact with the protrusion 24. You may be in contact. From a manufacturing point of view, it is desirable that the size of the recess 25 of the permanent magnet 22 is larger than the protrusion 24 of the rotor core 21 in order to prevent crossing or chipping of the permanent magnet during manufacturing. Further, considering the increase in torque ripple and cogging torque due to the influence of the attachment deviation of the permanent magnet 22, it is possible to minimize the deviation of the attachment position by shifting to a certain surface.
- FIG. 9 is a cross-sectional view in which the permanent magnet synchronous motor according to the second embodiment is cut perpendicularly to the axial direction, and the vicinity of the permanent magnet 22 is enlarged in the same manner as in FIG. Although not shown in FIG. 9, it is composed of a stator 10 and a rotor 20 as in FIG. 1.
- the permanent magnet synchronous motor according to the present embodiment is different from the permanent magnet synchronous motor according to the first embodiment in the following points.
- the concave portion of the permanent magnet 22 has three portions of the concave portion 251a, the concave portion 251b, and the concave portion 251c, and the protrusion protruding in the radial direction from the rotor core 21 has three protrusions 241a, the protrusion 241b, and the protrusion 241c. ing.
- the recess 251a located in the central portion of the permanent magnet 22 and the protrusion 241a are located on the outermost diameter side.
- the rotor core has an odd number of protrusions per pole, and has a protrusion aggregate having a plurality of protrusions as a set of protrusions.
- the shortest distance L2 from the outer diameter arc portion is formed in L1 ⁇ L2.
- the shortest distance L1 in the first embodiment is the shortest distance between the outermost portion of the recess 251a of the permanent magnet 22 and the outer diameter arc of the permanent magnet 22. Further, as shown in FIG. 9, the shortest distance L2 referred to in the first embodiment is the tangent line TL in contact with the outermost portion of the recess 251a of the permanent magnet 22, the sticking surface AS and the recess 251b of the permanent magnet 22, or the recess 251b.
- the recess 251b and the recess 251c have the same dimensions, but they do not necessarily have the same dimensions. However, from the viewpoint of reducing torque ripple, cogging torque, etc., it is desirable that the dimensions are the same.
- FIG. 10 is a diagram showing the demagnetization rate distribution of the permanent magnet 22 according to the second embodiment and the demagnetization rate distribution of the prior art for comparison.
- FIG. 10A shows L1> L2
- FIG. 10B shows the demagnetization rate distribution in the case of the second embodiment.
- the dark part indicates that the demagnetization rate is high, and the light part indicates that the demagnetization rate is low.
- FIG. 10 it can be seen that in the second embodiment as well, the distribution with a high demagnetization rate is narrowed as in the first embodiment.
- FIGS. 11 and 12 are diagrams showing the form of L1> L2 as in the prior art, the induced voltage before demagnetization and the induced voltage decrease rate after demagnetization in the second embodiment.
- each figure is a diagram standardized with the induced voltage and the induced voltage decrease rate of the prior art as 1.
- the induced voltage of the second embodiment is larger than that of the prior art, and the rate of decrease of the induced voltage due to demagnetization is smaller than that of the prior art.
- FIG. 13 and 14 are partially enlarged views of the modified form 1 and the modified form 2 of the permanent magnet synchronous motor according to the second embodiment, and are different from FIG. 9 in the following points.
- the protrusions 241a to 241c of the rotor core 21 and the recesses 251a to 251c of the permanent magnet 22 have different shapes, and the permanent magnets 22 are not completely fitted between the protrusions 241a and the protrusions 241b, or between the protrusions 241a and the protrusions 241c.
- the void in FIG. 14 is larger than the void in FIG.
- Nd-Fe-B type magnets used for permanent magnets are expensive because they use heavy rare earths.
- the amount of permanent magnet 22 used can be reduced and the cost can be reduced.
- the processing of permanent magnets can be facilitated, and the cost for processing can be reduced.
- the induced voltage is slightly reduced by the configuration as shown in FIGS. 13 and 14, there is no problem because the same effect as that of the second embodiment can be obtained.
- FIG. 15 is a partially enlarged view of the modified form 3 of FIG. 9 showing the second embodiment, except that the protrusions 241a to 241c and the recesses 251a to 251c are rectangular and different in shape. It has the same configuration as. Therefore, there is no problem because the same effect as that of the second embodiment can be obtained.
- FIGS. 9 and 13 to 17 are partially enlarged views of the modified forms 4 and 5 which are modified examples of FIGS. 13 and 14 shown as the modified forms of the second embodiment.
- 13 and 14 have the same configuration except that the protrusions 241a to 241c and the recesses 251a to 251c have rectangular shapes and are different from each other. Therefore, it is possible to obtain the same effect as that of the second embodiment, and there is no problem.
- the permanent magnets shown in FIGS. 9 and 13 to 17 have a shape having three protrusions, but there is no problem even if the number of protrusions is an odd number of 3 or more. ..
- FIG. 18 is an enlarged view of the vicinity of the permanent magnet of the rotor of the permanent magnet synchronous motor according to the third embodiment, and is a cross-sectional view cut perpendicular to the axial direction of the shaft.
- FIG. 18 differs from the first embodiment in the following points.
- the number of protrusions protruding from the rotor core 21 is two, and the number of recesses of the permanent magnet 22 is also two.
- the shortest distance L1 is the shortest distance between the outermost portion of the recess 252a or the recess 252b of the permanent magnet 22 and the outer diameter arc of the permanent magnet, and unlike the first and second embodiments, it is not near the center of the permanent magnet. Further, the shortest distance L2 is defined below.
- a tangent TL that is in contact with the outermost portion of the recess 252a or the recess 252b of the permanent magnet is defined.
- the rotor core has an even number of protrusions per pole, and has a protrusion aggregate having a plurality of protrusions as a set of protrusions.
- the shortest distance L2 between the permanent magnet and the outer diameter arc portion of the permanent magnet is formed in L1 ⁇ L2.
- FIG. 19 is a diagram showing the demagnetization rate distribution of the permanent magnet 22 according to the third embodiment and the demagnetization rate distribution of the prior art for comparison.
- FIG. 19A shows L1> L2
- FIG. 19B shows the demagnetization rate distribution in the case of the second embodiment.
- the dark part indicates that the demagnetization rate is high, and the light part indicates that the demagnetization rate is low.
- FIG. 19 it can be seen that in the third embodiment as well, the distribution with a high demagnetization rate is narrowed as in the first and second embodiments.
- FIG. 20 is a result of standardizing the induced voltage of L1> L2, which is the prior art, as 1, and comparing it with the induced voltage of the present embodiment.
- FIG. 21 is a diagram in which the induced voltage reduction rate of L1> L2, which is the prior art, is standardized as 1, and compared with the induced voltage reduction rate of the present embodiment.
- the induced voltage is improved by the present embodiment.
- the rate of decrease in the induced voltage is decreasing. This is due to the effect of eliminating the magnet recess near the center of the magnet, and the fundamental wave of the gap magnetic flux density of the magnet that contributes to the torque generated between the stator 10 and the rotor 20 has increased. Therefore, it is possible to increase the torque in the low speed range, and it is also possible to suppress the decrease in the magnet magnetic flux due to the irreversible demagnetization generated by the demagnetizing field at high temperature. That is, it is possible to suppress a decrease in torque at high temperatures.
- FIG. 22 is a partially enlarged view of the modified form 1 of the permanent magnet synchronous motor according to the third embodiment, and is different from FIG. 18 in the following points.
- FIG. 22 is different in that the permanent magnet 22 sandwiched between the two protrusions 242a and 242b does not extend to the rotor core 21 but is halfway.
- the reason for adopting this embodiment is that if the circumferential width of the portion sandwiched between the protrusions 242a and 242b is narrow, the magnet may be cracked or chipped, and may not be manufactured. Therefore, in consideration of production possibility, it is desirable that the bottom surface of the permanent magnet 22 has a structure located on the outer diameter side rather than the outer peripheral side.
- the protrusions and recesses are centered in the circumferential direction of the permanent magnet 22.
- It is a shape that is a mirror object as a base axis.
- the shape configuration of the protrusions and recesses by the mirror surface object is the same in other embodiments such as the first embodiment and the second embodiment, and the mirror surface object is based on the radiation RL in each embodiment. It has become.
- the outermost shape of the portion forming the shortest distance L2 in the concave portion is an arc shape
- the modified form 5 of FIG. 26 has an arc shape.
- the shape of the portion forming the shortest distance L2 is formed diagonally. Also in these modified forms, the effect of the third embodiment can be obtained in the same manner.
- FIG. 27 is a cross-sectional view showing a configuration in which the rotor portion of the permanent magnet synchronous motor according to the fourth embodiment is cut perpendicular to the axial direction of the shaft.
- the basic configuration is the same as that of the first to third embodiments, and differs in the following points.
- a slit 26 is provided in the rotor core 21 of the rotor. By arranging the slit 26, it is possible to reduce the q-axis inductance Lq in the permanent magnet synchronous motor.
- FIGS. 28 and 29 corresponds to the configuration of FIG. 2
- FIG. 28 corresponds to the configuration of FIG. 9
- FIG. 29 corresponds to the configuration of FIG. 27 to 29 are examples of slit arrangements. It is not limited to these as long as the slit is arranged so that the magnetic resistance becomes large with respect to the q-axis magnetic flux ⁇ q in the permanent magnet synchronous motor. Further, although two slits are arranged per pole in FIGS. 27 to 29, there is no problem even if more slits are arranged.
- stator 10 stator, 11 stator core, 12 core back, 14 coil, 20 rotor, 21 rotor core, 22 permanent magnet, 23 shaft, 24,241a, 241b, 241c, 242a, 242b protrusion, 25,251a, 251b, 251c, 252a, 252b Recess
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Abstract
Description
一般的に、表面磁石型の永久磁石同期モータが発生するトルクTは、
q軸電流Iqが必要であるからq軸電流Iqの減少はトルク低下につながる。このため、高回転または高速時に大トルクを出力するには、小さなd軸電流Idで効果的な弱め磁束制御を行う必要がある。これを行うためにd軸インダクタンスLdを大きくし、小さなd軸電流Idで効果的な弱め磁束制御を行う技術として以下の先行技術文献がある。
本先行技術では、ロータコア表面に配置された複数の永久磁石に嵌るように、ロータコアから径方向に突出した突起を形成することでd軸インダクタンスLdを大きくし弱め界磁制御を効果的に機能させ高回転時のトルク出力を改善している。
実施の形態1に係る永久磁石同期モータについて説明する。図1は、本実施の形態に係る永久磁石同期モータ100を軸方向と垂直に切断した構成を示す断面図である。ここで、永久磁石同期モータ100におけるロータ20の軸心に沿う方向を軸方向とする。軸方向に垂直なロータ20の断面において、ロータ20の半径に沿う方向を径方向とする。ロータ20の回転方向に沿う方向、すなわち、上記断面においてロータ20の軸心を中心とした円周に沿う方向を周方向とする。
永久磁石同期モータは、モータ入力電圧Viを越える端子電圧Vtを発生してトルクTを出力することができない。一般的に、回転数が上がると次式(1)~(4)で示す式に従って端子電圧Vtが増大する。
Vt=√(Vd2+Vq2)・・・(1)
Vd=RId+ωLqIq・・・(2)
Vq=RIq+ωΦm+ωLdId・・・(3)
ω=2πf=2π(N/60)pn・・・(4)
ここで、Vd、Vqはdq軸電圧、Rは相抵抗、Id、Iqはdq軸電流、Φmは磁石磁束、Ld、Lqはdq軸インダクタンス、ωは角速度、fは周波数、Nは1分間当たりの回転数、pnは極対数である。永久磁石同期モータでは、高回転におけるトルク出力を増大させる制御方式として、端子電圧増大を抑制する、所謂、弱め磁束制御がある。この弱め磁束制御は磁石磁束Φmを弱める方向にd軸電流Idを通電する制御方式であるが、d軸インダクタンスLdが小さい場合、大きなd軸電流Idを流す必要がある。しかしながら、モータに通電することができる電流には上限があり、インバータからモータに供給する電流をIinvとすると、次式(5)となる。
√3×Iinv=√(Id2+Iq2)・・・(5)
T=PnΦmIq・・・(6)
であるから、d軸電流Idが増大するとトルクTを出力するためのq軸電流Iqが減少しトルク出力が低下する。従って、高回転でのトルクTを大きくするには少ないd軸電流Idで弱め磁束制御を効果的に得る必要があり、d軸インダクタンスLdを増大する必要がある。このために、図3に示す構造とすることでd軸インダクタンスLdを向上することができる。図4は、横軸を速度(回転数)、縦軸をトルク出力とした速度‐トルク特性と呼ばれるものである。図4に示すように、突起24、および、凹部25を適用することにより、高回転数(高速度)でのトルク出力が増大していることが分かる。
Pc≒Hm/gm・・・(7)
本実施の形態1では、図1、2に示すように、永久磁石22の外径と凹部25の最短距離L2がL1≦L2となるように永久磁石22の凹部25を円弧形状としている。
実施の形態2に係る永久磁石同期モータについて説明する。図9は、本実施の形態2に係る永久磁石同期モータを軸方向と垂直に切断し、図2と同様に永久磁石22の近傍を拡大した断面図である。図9には、図示していないが図1と同様にステータ10、ロータ20によって構成されている。
永久磁石22の凹部は、凹部251a、凹部251b、凹部251cの3か所を有しており、ロータコア21から径方向に突出する突起は、突起241a、突起241b、突起241cの3つを有している。
また、本実施の形態2において、図9に示すように、永久磁石22の中央部に位置する凹部251a、および、突起241aが最も外径側に位置している。
ロータコアは1極当たり奇数個の突起を有し、複数の突起を1組の突起とする突起集合体を有し、突起集合体の周方向外側において、凹部は周方向外側の凹部と永久磁石の外径円弧部との間の最短距離L2がL1≦L2に形成されている。
ここで、図9において、凹部251b、凹部251cは同じ寸法となっているが、必ずしも、同じ寸法である必要はない。しかしながら、トルクリップル、コギングトルク等を低減する観点から考慮すると、同じ寸法である方が望ましい。
図10は、本実施の形態2に係る永久磁石22の減磁率分布と、比較となる先行技術の減磁率分布を示した図である。図10(a)はL1>L2、図10(b)は実施の形態2の場合における減磁率分布を示している。濃い部分は減磁率が高く、淡い部分は減磁率が低いことを表示している。図10に示すように、実施の形態2においても実施の形態1と同様に減磁率高い分布が狭くなっていることが分かる。また、図11、図12は、先行技術のようなL1>L2の形態と本実施の形態2における減磁前の誘起電圧と減磁後の誘起電圧低下率を示した図である。ここで、各図は先行技術の誘起電圧と誘起電圧低下率を1として規格化した図である。
以上のことから、永久磁石22に複数の凹部、および、ロータコア21に複数の突起を有する図9の形態とすることにより先行技術と比較してモータの特性低下を抑制することが可能となる。また、速度―トルク特性の高速域の出力増大効果は、突起を有しているため図4同様に得ることが可能である。
ロータコア21の突起241a~241cと、永久磁石22の凹部 251a~251cは、形状が異なり、突起241aと突起241b、または、突起241aと突起241cの間に永久磁石22が全て嵌っていなく、空隙を有している。図14における空隙は、図13における空隙より大きくなっている。一般的に、永久磁石に使用されるNd-Fe-B系の磁石は重希土類を使用しているため、高価である。このような構成にすることで、永久磁石22の使用量を削減し、コスト低減が可能となる。また、永久磁石の加工を容易にすることもでき、加工のための費用を削減することができる。
図13、図14のように構成することで、誘起電圧は多少低下するものの、実施の形態2と同様の効果を得られるため問題ない。
本実施の形態2として図9、図13~図17に示した永久磁石は、3つの突起を有した形状となっているが、突起の数は3以上の奇数で構成されていても問題ない。
実施の形態3に係る永久磁石同期モータについて説明する。図18は、本実施の形態3に係る永久磁石同期モータのロータの永久磁石付近を拡大した図で、シャフトの軸方向と垂直に切断した断面図である。
このように、ロータコアは1極当たり偶数個の突起を有し、複数の突起を1組の突起とする突起集合体を有し、突起集合体の周方向外側において、凹部は周方向外側の凹部と永久磁石の外径円弧部との間の最短距離L2がL1≦L2に形成されている。
図19は、本実施の形態3に係る永久磁石22の減磁率分布と、比較となる先行技術の減磁率分布を示した図である。図19(a)はL1>L2、図19(b)は実施の形態2の場合における減磁率分布を示している。濃い部分は減磁率が高く、淡い部分は減磁率が低いことを表示している。図19に示すように、実施の形態3においても実施の形態1、2と同様に減磁率高い分布が狭くなっていることが分かる。図20は、先行技術であるL1>L2の誘起電圧を1として規格化し、本実施の形態の誘起電圧と比較した結果である。また、図21は、先行技術であるL1>L2の誘起電圧低下率を1として規格化して、本実施の形態の誘起電圧低下率と比較した図である。
図22は、2個の突起242a、突起242bに挟まれた永久磁石22がロータコア21まで伸びておらず途中までとなっている点が異なる。本形態とする理由としては、突起242a、突起242bに挟まれた部分の周方向幅が狭い場合、磁石の割れあるいは欠けが発生する可能性がある他、製造できない可能性がある。このため、生産可能性を考えた場合、永久磁石22の底面が外周側よりも外径側に位置する構造となる方が望ましい。この構成においても図18に示した本実施の形態3と同様の効果を得ることが可能である。
また、図23に示したように、突起242a、突起242bに挟まれたロータコアが外径側に位置する変形形態2も考えられる。本変形形態2においても、実施の形態3の効果を同様に得ることが可能である。
また、図24の変形形態3および図25の変形形態4は、凹部において、最短距離L2を形成する部分の形状は最外部形状が円弧形状となっており、また、図26の変形形態5は、凹部において、最短距離L2を形成する部分の形状は斜めに形成されている。これらの変形形態においても、実施の形態3の効果を同様に得ることができる。
実施の形態4に係る永久磁石同期モータについて説明する。図27は、本実施の形態4に係る永久磁石同期モータにおけるロータ部分をシャフトの軸方向と垂直に切断した構成を示す断面図である。基本的な構成は、実施の形態1~3と同様であり、以下の点で異なる。
本実施の形態では、図27に示したようにロータのロータコア21にスリット26が設けられている。本スリット26を配置することにより、永久磁石同期モータにおけるq軸インダクタンスLqを低減することが可能となる。従って、前述の式(1)~式(4)に記載のωLqIqを低下させることができ、d軸電圧Vdの低減および端子電圧Vtの低減につながる。つまり、電圧飽和を緩和することにつながり速度―トルク特性を増大することが可能となる。
図28、図29も同様にスリット26が配置されている。なお、図27は図2の構成に対応し、図28は図9の構成に対応し、図29は図18の構成に対応している。
図27~図29はスリット配置の一例である。永久磁石同期モータにおけるq軸磁束Φqに対して磁気抵抗が大きくなるようにスリットを配置するものであれば、これらに限定されない。また、図27~図29においてスリットは1極当たり2本配置されているが、それ以上配置されていても問題ない。
従って、例示されていない無数の変形例が、本願明細書に開示される技術の範囲内において想定される。例えば、少なくとも1つの構成要素を変形する場合、追加する場合または省略する場合、さらには、少なくとも1つの構成要素を抽出し、他の実施の形態の構成要素と組み合わせる場合が含まれるものとする。
Claims (11)
- ステータと、前記ステータと空隙を介して配置されるロータから構成される永久磁石同期モータであって、
前記ロータは、磁性体によって構成されたロータコアを有し、前記ロータコアの表面には複数の永久磁石が配置され、前記永久磁石の形状は、前記ステータと対向する面の形状が円弧形状となっており、
前記ロータコアには、前記ステータのステータコアに向かって径方向に突出した1つ以上の突起を有し、前記永久磁石は、前記突起が嵌る凹部を有しており、
前記凹部の最外部と、前記永久磁石の外径円弧部との最短距離をL1、
前記凹部の最外部の接線と、前記永久磁石と前記ロータコアの貼付面から前記永久磁石の凹部への切り替えとなる点を始点として、前記ロータのシャフト中心から前記永久磁石の中心に向かう放射線に平行な平行線との交点を通過し、前記凹部と前記外径円弧部との最短距離L2としたときに、
L1≦L2となる前記凹部を有する前記永久磁石を備えたことを特徴とする永久磁石同期モータ。 - 前記凹部と前記突起の少なくとも1面が接していることを特徴とする請求項1に記載の永久磁石同期モータ。
- 前記凹部において、最短距離L2を形成する部分の形状は、最外部形状が円弧形状となっていることを特徴とする請求項1または請求項2に記載の永久磁石同期モータ。
- 前記凹部において、最短距離L2を形成する部分の形状は、斜めに形成されていることを特徴とする請求項1または請求項2に記載の永久磁石同期モータ。
- 前記ロータコアは1極当たり複数個の突起を有し、複数の前記突起を1組の突起とする突起集合体を有し、前記突起集合体の周方向外側において、前記凹部は周方向外側の前記凹部と前記永久磁石の外径円弧部との間の最短距離L2がL1≦L2に形成されていることを特徴とする請求項1から請求項4の何れか1項に記載の永久磁石同期モータ。
- 前記凹部の数は、3以上の奇数であることを特徴とする請求項1から請求項5の何れか1項に記載の永久磁石同期モータ。
- 前記凹部の数は、2以上の偶数であることを特徴とする請求項1から請求項5の何れか1項に記載の永久磁石同期モータ
- 前記突起の数は、3以上の奇数であることを特徴とする請求項6または請求項7に記載の永久磁石同期モータ。
- 前記突起の数は、2以上の偶数であることを特徴とする請求項7に記載の永久磁石同期モータ。
- 前記複数の凹部および前記複数の突起は、前記永久磁石の周方向中央を基軸として、鏡面対象であることを特徴とする請求項6から請求項9の何れか1項に記載の永久磁石同期モータ。
- 前記ロータには、永久磁石同期モータにおけるq軸磁束Φqに対して磁気抵抗が増大するようにスリットを設けたことを特徴とする請求項1から請求項10の何れか1項に記載の永久磁石同期モータ。
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