JP2010183778A - Electric motor and method of controlling the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve both a torque in a low-speed area and high efficiency under weak magnetic flux control in a high-speed area. <P>SOLUTION: A moving member 1 and a stator (armature) 20 are disposed to be counter to each other across an air gap 15. The moving member 1 is formed by embedding an N pole 2 and an S pole 3 alternately in a moving member core 4. The N pole 2 has a high coercivity magnet 2a and a low coercivity magnet 2b. The low coercivity magnet 2b is placed on the front side in the direction of drive of the moving member 1, while the high coercivity magnet 2a is placed on the rear side in the direction of drive of the moving member 1. The S pole 3 has a high coercivity magnet 3a and a low coercivity magnet 3b. The low coercivity magnet 3b is placed on the front side in the direction of drive of the moving member 1, while the high coercivity magnet 3a is placed on the rear side in the direction of drive of the moving member 1. At high rotation operation, an angle of lead of the current phase of the stator 20 is advanced temporarily to demagnetize the low coercivity magnets 2b and 3b, and then the angle of lead is set back to the original to obtain weak magnetic flux. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric motor including a permanent magnet in a mover and a control method thereof.

  In an electric motor equipped with a permanent magnet type mover, a magnet having a large coercive force and a small magnetomotive force is arranged in a portion where the armature reaction is easy to demagnetize, and a coercive force is small and the magnetomotive force is large in a portion where the armature reaction is small. There are known techniques for improving the demagnetization resistance and increasing the maximum torque and efficiency of an electric motor by arranging magnets (for example, Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 10-112946 WO2003 / 079516

  However, in an electric motor equipped with the conventional permanent magnet type mover described above, when the amount of magnets is increased in order to obtain a large amount of low-speed torque, or when a magnet having a large magnetomotive force is used, the induced voltage becomes the power supply voltage in the high-speed rotation region. When the level is exceeded, it is necessary to control the magnetic flux weakening to reduce the induced voltage, which causes a reduction in efficiency. In a wound field type motor, the magnetic flux can be weakened in a high-speed rotation range, but a field current is always required, and it is difficult to improve efficiency.

  In order to solve the above-described problems, the present invention provides a motor including a permanent magnet type mover, wherein each of the magnetic poles provided on the mover includes a plurality of permanent magnets having different coercive forces arranged in the drive direction of the mover. And the coercive force of the magnet arrange | positioned at the drive direction front side was made lower than the coercive force of the magnet arrange | positioned at the drive direction rear side.

  According to the present invention, in the state where no d-axis current is passed, the demagnetization of the magnet on the low coercive force side does not occur, a large magnetic flux can be obtained, and by applying the d-axis current in the high rotation range, the low coercive force side As a result, the magnetic flux is weakened and the induced voltage can be lowered, so that the variable speed range is expanded.

  In addition, since the amount of high coercivity magnets such as Nd—Fe—B based on rare earths with limited resources can be reduced, a significant cost reduction effect can be obtained.

It is a schematic cross section which shows the structure of Example 1 of the electric motor which concerns on this invention. (A) The figure explaining the magnetic flux change by the demagnetization of Example 1, (b) The figure explaining the change of the magnetic flux component by the demagnetization of Example 1. FIG. (A) It is a needle | mover schematic sectional drawing explaining the case where (beta) = 0 degrees in the electric motor of Example 1. FIG. (B) It is a needle | mover schematic sectional drawing explaining the mode of a demagnetization in the case of (beta) = 45 degrees in the electric motor of Example 1. FIG. (C) It is a needle | mover schematic sectional drawing explaining the mode of a demagnetization in the case of (beta) = 90 degrees in the electric motor of Example 1. FIG. (A) It is a needle | mover schematic sectional drawing explaining the case where (beta) = 0 degrees in the electric motor of Example 2. FIG. (B) It is a needle | mover schematic sectional drawing explaining the mode of a demagnetization in the case of (beta) = 45 degrees in the electric motor of Example 2. FIG. (C) It is a needle | mover schematic sectional drawing explaining the mode of a demagnetization in the case of (beta) = 90 degrees in the electric motor of Example 2. FIG. (A) It is a needle | mover schematic sectional drawing explaining the mode of a demagnetization in the case of (beta) = 0 degree at the time of forward rotation in the electric motor of Example 3. FIG. (B) It is a needle | mover schematic sectional drawing explaining the mode of a demagnetization in the case of (beta) = 45 degrees at the time of forward rotation in the electric motor of Example 3. FIG. (A) It is a needle | mover schematic sectional drawing explaining the mode of a demagnetization in the case of (beta) = 0 degree at the time of inversion in the electric motor of Example 3. FIG. (B) It is a needle | mover schematic sectional drawing explaining the mode of a demagnetization in the case of (beta) = 45 degrees at the time of inversion in the electric motor of Example 3. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, each embodiment described below is applied not only to rotary motors such as an inner rotor type electric motor, an outer rotor type electric motor, and an axial gap type, but also to a linear drive type linear motor device.

  FIG. 1 is a schematic cross-sectional view of a first embodiment of an electric motor according to the present invention. In FIG. 1, a mover 1 and a stator (armature) 20 are arranged to face each other with an air gap 15 interposed therebetween. The mover 1 is formed by alternately embedding the N pole 2 and the S pole 3 in the mover core 4. The N pole 2 includes a high coercivity magnet 2a having a relatively high coercivity and a low coercivity magnet 2b having a relatively low coercivity. The low coercivity magnet 2b is disposed on the front side in the driving direction of the mover 1, and the high coercivity magnet 2a having a higher coercivity than the low coercivity magnet 2b is disposed on the rear side in the driving direction of the mover 1. Similarly, the S pole 3 includes a high coercivity magnet 3a having a relatively high coercivity and a low coercivity magnet 3b having a relatively low coercivity. The low coercivity magnet 3 b is disposed on the front side in the driving direction of the mover 1, and the high coercivity magnet 3 a having a higher coercivity than the low coercivity magnet 3 b is disposed on the rear side in the driving direction of the mover 1.

  For the high coercive force magnets 2a and 3a, for example, neodymium magnets (Nd-Fe-B magnets) are used. As the low coercive force magnets 2b and 3b, for example, ferrite magnets or alnico magnets having a coercive force lower than those of neodymium magnets are used.

  The stator 20 includes a stator core 21 and a winding 24. Teeth 22 and slots 23 are periodically formed in a stator core 21 in which electromagnetic steel plates are insulated and laminated. A winding 24 is wound around the slot 23. FIG. 1 is a developed view in which the air gap 15 is linear when the present invention is applied to a rotary motor.

  FIG. 2 is a diagram illustrating a magnetic flux and a magnetic flux component spectrum before and after demagnetization in the first embodiment. As shown in FIG. 2A, the peak value of the magnetic flux before demagnetization was about ± 0.93 [Wb], but the peak value of the magnetic flux after demagnetization is about ± 0.82 [Wb]. It is falling.

  FIG. 3 is a schematic cross-sectional view for explaining the demagnetizing action by the armature magnetic flux density distribution on the mover of the first embodiment, in which only the mover is illustrated and the stator (armature) is not illustrated. In addition, the same code | symbol is provided to the same component as FIG. 1, and the overlapping description is abbreviate | omitted.

  In the following description, β represents the difference between the voltage phase induced in the stator by the permanent magnet disposed on the mover and the current phase of the stator. 3A shows a case where β = 0 °, FIG. 3B shows a case where β = 45 °, and FIG. 3C shows a case where β = 90 °.

  In FIG. 3A, the armature magnetic flux density distribution 6a is set at a position advanced by 90 ° in electrical angle with respect to the magnetic flux density distribution 5 in the gap 15 in FIG. A portion where the magnet is exposed to the armature reaction at this time is indicated by an arrow 7. Although this armature reaction acts on the high coercivity magnets 2a and 3a, the low coercivity magnets 2b and 3b are not exposed to the demagnetizing field due to the armature reaction, and therefore no demagnetization occurs.

  FIG. 3B shows a state where β = 45 °. When the armature current is advanced to an armature magnetic flux density distribution 6b, demagnetization occurs due to the armature reaction on the low coercivity magnets 2b and 3b in the range indicated by the arrow 18, resulting in a decrease in the magnetic flux of the magnet. . Therefore, unlike the normal flux-weakening control, d-axis current that does not contribute to torque is not required in the high rotation range, and the efficiency is improved. In the low rotation range, a high torque can be obtained because of the normal magnetomotive force.

  FIG. 3C shows a state where β = 90 °. Further, when the armature current is advanced to an armature magnetic flux density distribution 6c, the range 18 where the armature reaction reaches the low coercive force magnets 2b and 3b is expanded, and the range where demagnetization occurs is expanded.

  As shown in FIG. 3, in an interior magnet type (Interior Permanent Magnet, IPM) structure having a salient pole ratio (or an inset type SPM (Surface Permanent Magnet)), β ≠ 0 ° during maximum torque control. However, according to the configuration of the present invention, demagnetization occurs in the low coercivity magnets 2b and 3b due to the advance angle, which is not preferable. Therefore, the boundary position 17 between the high coercive force magnet 2a and the low coercive force magnet 2b is set to β0, which is β at which the maximum torque obtained from the salient pole ratio of the mover (maximum thrust in the case of the linear drive type) is generated, By offsetting in advance, demagnetization at the time of maximum torque control can be prevented, and a decrease in maximum torque can be avoided.

  According to the present embodiment described above, the demagnetization of the magnet on the low coercive force side does not occur in the state where no d-axis current is passed, and a large magnetic flux can be obtained and the d-axis current is applied in the high rotation range. Since demagnetization occurs in the magnet on the low coercive force side, the magnetic flux is weakened as a result, and the induced voltage can be lowered, so that the variable speed range is expanded.

  In addition, since the amount of high coercivity magnets such as neodymium magnets using rare earths with limited resources can be reduced, there is an effect that the cost can be significantly reduced.

  Further, according to the present embodiment, the driving direction position of the boundary position between the high coercivity magnet and the low coercivity magnet is defined with respect to β at the maximum torque or maximum thrust operating point, so that it is low in the maximum torque state. There is an effect that it is possible to avoid demagnetization of the coercive force magnet and to prevent a decrease in the maximum torque or the maximum thrust.

  Next, a second embodiment in which the present invention is applied to an SPM type electric motor will be described. FIGS. 4A to 4C are schematic cross-sectional views illustrating a demagnetizing action by the armature magnetic flux density distribution for the mover of the second embodiment. FIG. 4 shows only the mover, and the illustration of the stator (armature) similar to that in FIG. 1 is omitted. In FIG. 4, the surface of the mover 1 facing the stator (not shown) is provided with an N pole 9 having a high coercivity magnet 9a and a low coercivity magnet 9b, and a high coercivity magnet 10a and a low coercivity magnet 10b. The S poles 10 are alternately formed without gaps.

  For the high coercive force magnets 9a and 10a, for example, neodymium magnets (Nd-Fe-B magnets) are used. For the low coercive force magnets 9b and 10b, for example, ferrite magnets or alnico magnets having a lower coercive force than neodymium magnets are used.

  4A shows a case where β = 0 °, FIG. 4B shows a case where β = 45 °, and FIG. 4C shows a case where β = 90 °. In FIG. 4A, an armature magnetic flux density distribution 6a is set at a position advanced by 90 ° in electrical angle with respect to the magnetic flux density distribution 5 of the gap. The range in which the magnet is exposed to the armature reaction at this time is indicated by an arrow 7. Although this armature reaction acts on the high coercivity magnets 9a and 10a, the low coercivity magnets 9b and 10b are not exposed to the demagnetizing field due to the armature reaction, and therefore no demagnetization occurs.

  FIG. 4B shows a state where β = 45 °. When the armature current is advanced to an armature magnetic flux density distribution 6b, the range 7 in which the magnet is exposed to the armature reaction is expanded, and the low coercivity magnets 9b and 10b in the range indicated by the arrow 18 have an armature reaction. It reaches. This causes demagnetization of the low coercivity magnets 9b and 10b, resulting in a decrease in the magnetic flux of the magnet. Therefore, unlike the normal flux-weakening control, d-axis current that does not contribute to torque is not required in the high rotation range, and the efficiency is improved. In the low rotation range, a high torque can be obtained because of the normal magnetomotive force.

  FIG. 4C shows a state where β = 90 °. Further, when the armature current is advanced to become the armature magnetic flux density distribution 6c, the range 18 in which the armature reaction reaches the low coercive force magnets 9b and 10b is expanded and the armature reaction is strengthened. Expands and magnetic flux decreases further.

  In this embodiment, low coercivity magnets 9b and 10b are arranged between the high coercivity magnets 9a and 10a. Therefore, even if the driving direction of the mover 1 is reversed by reversing the polarity of the low coercive force magnets 9b and 10b by the armature current advance angle from the state of FIG. A configuration in which a coercive magnet is disposed and a high coercive magnet is disposed on the rear side in the driving direction is obtained.

  At this time, as the polarity of the low coercivity magnet is reversed, the center position of the magnetic pole is offset by 90 ° by the electrical angle that is the driving direction length of the low coercivity magnet, so the reference position of the current phase angle of the armature is offset by the magnetic pole offset. And control so that the electrical angle is offset by 90 °.

  According to the present embodiment described above, since the high coercivity magnet and the low coercivity magnet are alternately arranged, by reversing the polarity of the low coercivity magnet, even when the mover rotation direction is reversed, In a state where no d-axis current flows, demagnetization of the magnet on the low coercivity side does not occur, a large magnetic flux can be obtained, and demagnetization occurs in the low coercivity magnet by applying the d-axis current in the high rotation range. As a result, the magnetic flux is weakened, and the induced voltage can be lowered, so that the variable speed range is expanded.

  In addition, according to the present embodiment, the amount of high coercivity magnets such as Nd—Fe—B system using rare earth, which is limited in resources, can be reduced, so that there is an effect that the cost can be greatly reduced.

  Further, according to the present embodiment, the polarity of the low coercivity magnet disposed between the high coercivity magnets is reversed with the reversal of the rotation direction of the mover, so that the phase of the magnetic pole center position is in the mover drive direction. Offset by the length of the low coercivity magnet. By following this and correcting the reference position of the current phase, a configuration in which a low coercivity magnet is arranged on the front side in the driving direction of each magnetic pole and a high coercivity magnet is arranged on the rear side in the driving direction even when the driving direction is reversed. There is an effect that it is.

  Next, a third embodiment of the electric motor according to the present invention will be described with reference to FIGS. In this embodiment, each magnetic pole is composed of three magnets having different coercive forces, a high coercive magnet is arranged at the center in the driving direction of each magnetic pole, and low coercive magnets are arranged at the front and rear ends of each magnetic pole in the driving direction. This is an example of arrangement. FIG. 5 shows a state in which the rotating electrical machine is normally rotated or a linear drive type device is driven in the right direction in the drawing. FIG. 6 shows the time when the rotating electrical machine is rotated in the reverse direction or when the linear drive type device is driven in the left direction in the figure.

  5A and 5B, an N pole 11 and an S pole 12 are formed on the surface of the mover 1 that faces a stator (not shown). The N pole 11 includes a high coercivity magnet 11a and low coercivity magnets 11b and 11c. The high coercive force magnet 11 a is disposed in the central portion in the driving direction of the N pole 11. The low coercivity magnet 11 c is disposed at the front end of the N pole 11 in the driving direction, and the low coercivity magnet 11 b is disposed at the rear end of the N pole 11 in the driving direction.

  Similarly, the south pole 12 includes a high coercivity magnet 12a and low coercivity magnets 12b and 12c. The high coercive force magnet 12 a is disposed at the center in the driving direction of the S pole 12. The low coercivity magnet 12 c is disposed at the front end of the S pole 12 in the driving direction, and the low coercivity magnet 12 b is disposed at the rear end of the S pole 12 in the driving direction.

  As the high coercivity magnets 11a and 12a, for example, neodymium magnets (Nd-Fe-B magnets) are used. For the low coercivity magnets 11b, 11c, 12b, and 12c, for example, a ferrite magnet or an alnico magnet is used that has a lower coercivity than a neodymium magnet.

  A mover core 4 made of a soft magnetic material is provided between the N pole 11 and the S pole 12 to form an inset SPM structure or an IPM structure.

  FIG. 5A shows the case of normal rotation and β = 0 °. In FIG. 5A, the armature magnetic flux density distribution 6a is set at a position advanced by 90 ° in electrical angle with respect to the magnetic flux density distribution 5 of the gap. A portion where the magnet is exposed to the armature reaction at this time is indicated by an arrow 7. This armature reaction acts on the high coercivity magnets 11a and 12a and the low coercivity magnets 11b and 12b. And since the armature reaction reaches the low coercive force magnets 11b and 12b in the range indicated by the arrow 18, demagnetization occurs, and as a result, the magnetic flux decreases. Therefore, unlike the normal flux-weakening control, d-axis current that does not contribute to torque is not required in the high rotation range, and the efficiency is improved. In the low rotation range, a high torque can be obtained because of the normal magnetomotive force.

  FIG. 5B shows the case of forward rotation and β = 45 °. When the armature current is advanced to the armature magnetic flux density distribution 6b, the demagnetization is the same in the range 18 in which the armature reaction reaches the low coercivity magnets 11b and 12b.

  6A shows the case of inversion and β = 0 °, and FIG. 6B shows the case of inversion and β = 45 °. Since the structures of the N pole 11 and the S pole 12 are symmetric with respect to the mover driving direction and the opposite direction, the action of the armature magnetic flux distributions 6a and 6b on the low coercive force magnet is switched between 11b and 11c, and 12b And 12c are interchanged, which is the same as in the forward rotation of FIG.

  According to this embodiment, even in the configuration of an IPM structure electric motor having an salient pole ratio or an inset SPM structure electric motor, the armature can be reversed in the high rotation range while enabling the moving direction (or rotation direction) of the mover to be reversed. By demagnetizing the low coercivity magnet by the phase advance angle of the current and then returning the advance angle to decrease the d-axis current, the d-axis current that does not contribute to the torque can be reduced and the efficiency can be increased. There is.

  In addition, since the amount of high coercivity magnets such as Nd—Fe—B based on rare earth, which has limited resources, can be reduced, there is an effect that the cost can be greatly reduced.

DESCRIPTION OF SYMBOLS 1 Movator 2 N pole 2a High coercive force magnet 2b Low coercive force magnet 3 S pole 3a High coercive force magnet 3b Low coercive force magnet 4 Movable core 20 Stator 21 Stator core 22 Teeth 23 Slot 24 Winding

Claims (7)

In an electric motor having a stator and a mover having a permanent magnet,
Each magnetic pole provided on the mover is configured by arranging a plurality of permanent magnets having different coercive forces in the drive direction of the mover, and a low coercivity magnet having a relatively low coercivity is arranged on the front side in the drive direction. An electric motor comprising a high coercivity magnet having a relatively high coercivity on the rear side in the driving direction.   When the difference between the voltage phase induced in the stator by the permanent magnet arranged on the mover and the current phase of the stator is β, and β that provides the maximum thrust or maximum torque is β0, the high coercivity magnet 2. The electric motor according to claim 1, wherein a boundary position between the low coercive force magnet and the low coercive force magnet is provided on the front side in the driving direction by an electrical angle of about β0 from the center in the moving direction of each magnetic pole.   A high coercivity magnet having a relatively high coercive force is disposed at the center in the driving direction of the magnetic pole, a low magnetomotive force magnet having a relatively low coercivity is disposed at both ends of the magnetic pole in the driving direction, and an N pole and an S pole. 2. The electric motor according to claim 1, wherein a mover core made of soft magnetic material is provided between the two.   2. The electric motor according to claim 1, wherein the mover has a surface magnet type structure in which a mover core is not provided at a boundary between the N pole and the S pole. An electric motor control method for controlling an electric motor according to claim 4,
A method for controlling an electric motor, comprising: reversing the polarity of low coercivity magnets arranged between high coercivity magnets having different polarities by armature reaction when reversing the drive direction of the mover.   6. The electric motor according to claim 5, wherein the reference position of the current phase angle is offset by an electrical angle corresponding to the length of the low coercivity magnet in the mover driving direction as the moving direction of the mover is reversed. Control method. An electric motor control method for controlling an electric motor according to any one of claims 1 to 4,
High rotational speed region where the induced voltage is larger than the armature drive voltage, where β is the difference between the voltage phase induced in the stator by the permanent magnet placed on the mover and the current phase of the stator The method of controlling an electric motor according to claim 1, wherein β is greatly advanced and the low holding magnet is demagnetized once, and then β is reduced.

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