JP2008125242A - Permanent magnet type synchronous electric motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly efficient and inexpensive permanent magnet-type synchronous electric motor where heat generation of a permanent magnet is suppressed and thermal demagnetization of the permanent magnet is prevented. <P>SOLUTION: The permanent magnet-type synchronous electric motor holding the permanent magnet 1 in a rotor core is provided with a conductor 2 which surrounds the permanent magnet 1 and reduces eddy current of the permanent magnet 1 and whose conductivity is higher than the that of permanent magnet 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a permanent magnet type synchronous motor.

  Conventionally, the permanent magnet 20 of a permanent magnet type synchronous motor (PM motor) (see FIG. 8) includes a rare earth sintered material such as high performance neodymium / iron / boron (NdFeB) in order to increase the efficiency and size of the motor. A magnet is used. The neodymium-based permanent magnet 20 has a property that it is weak against temperature change and has a much higher electrical conductivity than a ferrite permanent magnet or the like used previously. FIG. 8 shows the eddy current of the permanent magnet. As shown in FIG. 8, an eddy current J is generated in the permanent magnet 20 due to magnetic field fluctuations B due to slot harmonics, inverter carrier harmonics, etc., and eddy current loss due to this is no longer negligible. When the eddy current loss of the permanent magnet 20 increases, the temperature of the permanent magnet 20 increases, and thermal demagnetization is likely to occur under a condition in which a demagnetizing field is applied to the permanent magnet 20 such as during field-weakening control. Therefore, the permanent magnets 20 held by the rotor core 21 are divided in the axial direction as shown in FIG. 9A or in the circumferential direction (rotation direction) as shown in FIG. A method of reducing the eddy current loss of the permanent magnet 20 to make it difficult to demagnetize by providing an insulating layer 22 between them, and a permanent magnet 20 (for example, a samarium-cobalt (SmCo) magnet) that is resistant to temperature changes are used. Measures such as doing are taken. An example of such a technique is disclosed in the following Patent Documents 1 to 4. Patent Document 1 below discloses a permanent magnet 20 that is divided into a plurality of parts in the axial direction to reduce the generation of eddy currents. The following Patent Document 2 discloses a permanent magnet 20 that is divided into two or more in the axial direction to reduce eddy current loss. Patent Document 3 listed below discloses a technique for reducing the eddy current loss generated during field-weakening control by reducing the width of the permanent magnet 20 in the counter-rotating direction of the rotor core 21. Patent Document 4 listed below discloses a technique in which the permanent magnet 20 is divided in the circumferential direction to reduce eddy current loss.

JP 2005-354899 A JP 2005-204461 A JP 2004-96868 A JP 2000-228838 A

  However, as shown in FIG. 9, in the method of dividing the permanent magnet 20 in the axial direction or the circumferential direction, the eddy current loss decreases as the number of divisions of the permanent magnet 20 increases, and the risk of thermal demagnetization. However, as the number of divisions of the permanent magnet 20 increases, the labor (time) required for manufacturing the permanent magnet type synchronous motor increases, and the cost increases.

  Also, in the case of using a permanent magnet 20 (for example, a samarium / cobalt permanent magnet) that is resistant to temperature changes, rather than the neodymium permanent magnet 20 that is vulnerable to temperature changes, the performance is higher than that of the neodymium permanent magnet 20. Because it is inferior (weak magnetic force) and expensive, there must be some compromise on the efficiency, miniaturization, and cost of the permanent magnet synchronous motor.

  In view of the above, an object of the present invention is to provide a permanent magnet type synchronous motor that suppresses heat generation of the permanent magnet 20 to prevent thermal demagnetization of the permanent magnet 20 and is highly efficient and low in cost.

A permanent magnet synchronous motor according to a first invention (corresponding to claim 1) for solving the above-described problems is
In a permanent magnet type synchronous motor that holds a permanent magnet by a rotor core,
A permanent magnet type synchronous motor comprising a conductor having higher conductivity than the permanent magnet which surrounds the permanent magnet and reduces eddy current of the permanent magnet.

  A permanent magnet synchronous motor according to a second invention (corresponding to claim 2) for solving the above-mentioned problem is the permanent magnet synchronous motor according to the first invention, wherein the permanent magnet synchronous motor covers the surface of the conductor. A heat insulating material for preventing the heat of the conductor from being transmitted to the permanent magnet and the rotor core is provided.

  A permanent magnet synchronous motor according to a third invention (corresponding to claim 3) for solving the above problem is the permanent magnet synchronous motor according to the second invention, wherein the heat insulating material is a heat of the conductor. Is not installed on the surface of the conductor end of the rotor core end so as to suppress the temperature rise of the conductor.

  A permanent magnet synchronous motor according to a fourth invention (corresponding to claim 4) for solving the above problems is the permanent magnet synchronous motor according to the first invention, wherein the conductor is formed of a conductive wire. It is characterized by.

  A permanent magnet synchronous motor according to a fifth invention (corresponding to claim 5) for solving the above problems is the permanent magnet synchronous motor according to the first invention, wherein the conductor is the permanent magnet and the permanent magnet The heat conductivity is higher than that of the rotor core, and the heat radiation amount on the surface of the conductor end is larger than the heat generation amount of the conductor.

  According to the present invention, the eddy current loss of the permanent magnet can be greatly reduced by surrounding the permanent magnet of the permanent magnet type synchronous motor with the conductor. Further, due to the decrease in eddy current loss, the amount of heat generated by the permanent magnet is reduced, and the performance of the permanent magnet (permanent magnet type synchronous motor) can be prevented from being degraded and thermal demagnetization can be prevented.

  An embodiment of a permanent magnet type synchronous motor according to the present invention will be described with reference to FIGS. FIG. 1 is a perspective view of a conductor according to the first embodiment, FIG. 2 is a perspective view of a heat insulating material according to the second embodiment, and FIG. 3 is a perspective view of a conductor formed by a conductive wire according to the third embodiment. FIG. 4 is a perspective view of a conductor according to the fourth embodiment, FIG. 5 is a plan view of a permanent magnet type synchronous motor according to the present invention, and FIG. 6 is a diagram showing magnetic flux density over time at point A in FIG. FIG. 7 is a diagram showing magnet eddy current loss when there is a conductor surrounded by a conductor around a permanent magnet and when there is no conductor not surrounded by a conductor.

[First Embodiment]
First, a permanent magnet type synchronous motor according to the present invention will be described. As shown in FIG. 5, the permanent magnet type synchronous motor according to the present invention is a 12-pole 18-slot concentrated winding machine, and has an IPM (Interior Permanent Magnetic) structure in which the permanent magnet 1 is embedded in the rotor core 6. . On the side of the permanent magnet 1, a flux barrier 7, which is a space, is formed to prevent a short circuit of the magnetic flux of the permanent magnet 1. A stator core 8 is disposed on the outer side in the circumferential direction of the rotor core 6 so as to face the rotor core 6, and a winding 9 is disposed inside the stator core 8. In FIG. 5, only a part of the rotor core 6 and the stator core 8 is shown, but the rotor core 6 and the stator core 8 are actually formed in a cylindrical shape. In the present embodiment, the permanent magnet 1 is embedded in the rotor core 6 to hold the permanent magnet 1. However, in addition to such a structure, for example, a structure in which the permanent magnet 1 is installed on the surface of the rotor core 6. It is also possible.

  When the permanent magnet type synchronous motor is driven, a magnetic field fluctuation caused by the slot that is the winding groove of the winding 9 occurs in the permanent magnet 1, and an eddy current flows so as to cancel the magnetic field fluctuation, resulting in an eddy current loss. This eddy current loss becomes heat and the temperature of the permanent magnet 1 rises. FIG. 6 shows the time change of the magnetic flux density at the position indicated by point A in FIG. As shown in FIG. 6, at point A, it can be seen that the magnetic field fluctuation of the period three times as long as the slot occurs in the permanent magnet 1 with respect to one period of the current. When the temperature of the permanent magnet 1 rises due to eddy current loss, the residual magnetic flux density and the holding force of the permanent magnet 1 are reduced, so that the performance of the permanent magnet 1 is deteriorated and the efficiency of the permanent magnet synchronous motor is deteriorated. Further, when the field-weakening control driving of the permanent magnet type synchronous motor is performed, a magnetic field opposite to the magnetization direction of the permanent magnet 1 is applied to the permanent magnet 1. In the worst case, the permanent magnet 1 is demagnetized.

  Next, the structure of the principal part of the permanent magnet type synchronous motor according to the present embodiment will be described. As shown in FIG. 1, by surrounding the permanent magnet 1 with a conductor 2 (for example, an aluminum thin plate 3) having a higher conductivity than the permanent magnet 1, magnetic field fluctuations of the permanent magnet 1 are reduced, and eddy currents are reduced. Reduce heat generation due to loss. For the conductor 2, copper or the like can be used in addition to aluminum.

  Here, a comparison of the magnet eddy current loss in the case of the conductor 2 surrounded by the conductor 2 and the case of the conductor 2 not surrounded by the conductor 2 calculated by the magnetic field analysis by the finite element method is shown in FIG. Shown in Here, the value of the eddy current loss is normalized assuming that the eddy current loss of the magnet without the conductor 2 is 1. From FIG. 7, it can be seen that when the periphery of the permanent magnet 1 is surrounded by the conductor 2, the eddy current loss of the permanent magnet 1 is reduced to about 1/10 compared to the case without the conductor 2.

  Thus, according to the permanent magnet type synchronous motor according to the present embodiment, the eddy current loss of the permanent magnet 1 can be greatly reduced by surrounding the permanent magnet 1 of the permanent magnet type synchronous motor with the conductor 2. . Further, due to the decrease in eddy current loss, the amount of heat generated by the permanent magnet 1 is reduced, and the performance of the permanent magnet 1 (permanent magnet synchronous motor) can be prevented from being deteriorated and thermal demagnetization can be prevented.

[Second Embodiment]
A configuration of a main part of the permanent magnet type synchronous motor according to the present embodiment will be described. As shown in FIG. 7, in the first embodiment, instead of reducing the eddy current loss in the permanent magnet 1, eddy current loss in the conductor 2 occurs, so that the heat of the conductor 2 is transmitted to the permanent magnet 1. The permanent magnet 1 may be heated.

  For this reason, in this embodiment, as shown in FIG. 2, the surface of the conductor 2 was covered with a heat insulating material 4 having a low thermal conductivity. At that time, the conductor 2 located at the end of the permanent magnet type synchronous motor is exposed to the air, and the end face 2a of the conductor 2 is not provided with the heat insulating material 4, but the conductor 2 is exposed, and heat is released to the outside, The temperature rise of the conductor 2 can be reduced.

  Here, the heat insulating material 4 is a material that hardly transmits heat, and means a material having a thermal conductivity λ of λ = 0.06 W / mK (0.05 kcal / mh ° C.) or less. Examples of the heat insulating material 4 include an extruded polystyrene foam, a bead polystyrene foam, a rigid polyurethane foam, a polyethylene foam, a polypropylene foam, an isocyanurate foam, a phenol foam, and an inorganic fiber heat insulating material. , Glass wool, rock wool.

  As described above, according to the permanent magnet type synchronous motor according to the present embodiment, it is difficult to transfer heat generated by the conductor 2 to the permanent magnet 1 by covering the surface of the conductor 2 with the heat insulating material 4 having a low thermal conductivity. can do. In addition, the conductor 2 at the end of the permanent magnet type synchronous motor is exposed to the air. The heat insulating material 4 is not provided on the end surface 2a of the conductor 2 and the conductor 2 is exposed to release the heat of the conductor 2 to the outside. And the temperature rise of the conductor 2 can be suppressed.

[Third Embodiment]
A configuration of a main part of the permanent magnet type synchronous motor according to the present embodiment will be described. As shown in FIG. 5, a groove called a flux barrier 7 is usually formed on the side of the permanent magnet 1 of the permanent magnet type synchronous motor having an IPM structure in order to prevent a short circuit of the magnetic flux of the permanent magnet 1. In the case of the aluminum thin plate 3 (see FIG. 1) exemplified as the conductor 2 according to the first embodiment, the aluminum thin plate 3 is hard, and therefore the aluminum thin plate 3 is inserted at the stage of inserting the permanent magnet 1 into the rotor core 6. Must be inserted together, or the thin plate 3 should be U-shaped and the permanent magnet 1 must be inserted and then covered with a plate-like conductor made of the same material as the thin plate 3 to fix the permanent magnet 1 to the rotor core 6. Work efficiency will be reduced.

  For this reason, in this embodiment, as shown in FIG. 3, by using the conductor 5 instead of the thin plate 3 for the conductor 2, the conductor 5 is passed through the flux barrier 7 after the permanent magnet 1 is inserted to surround the permanent magnet 1. By short-circuiting 2, the same effect as in the first embodiment can be obtained. If this method is used, the first embodiment can be applied to an existing permanent magnet type synchronous motor.

  As described above, according to the permanent magnet type synchronous motor according to the present embodiment, in the case of the permanent magnet type synchronous motor having the IPM structure, the lead wire 5 is used for the flux barrier 7 by using the lead wire 5 for the conductor 2 surrounding the permanent magnet 1. The first embodiment can be applied to an existing permanent magnet type synchronous motor by surrounding the permanent magnet 1 and short-circuiting the conductor 2.

[Fourth Embodiment]
A configuration of a main part of the permanent magnet type synchronous motor according to the present embodiment will be described. In the present embodiment, as shown in FIG. 4, by using a material having high thermal conductivity for the conductor 2 surrounding the permanent magnet 1 without using the heat insulating material 4, the heat generated in the permanent magnet 1 and the conductor 2 are used. The generated heat is released from the end surface 2a of the conductor 2 to the outside as indicated by an arrow in FIG. Here, examples of the material having high thermal conductivity include pure aluminum Al (A1100): 222 W / (m · K) and pure copper Cu (C1100): 384 W / (m · K). In addition, in this embodiment, the structure which fixes the permanent magnet 1 and the conductor 2 to the rotor core 6 with the magnet spring board 10 is also applicable.

  In addition, when the amount of heat released from the end surface 2a of the conductor 2 is small and the amount of heat generated by the conductor 2 is large, the heat of the conductor 2 is transmitted to the permanent magnet 1 and the permanent magnet 1 may be thermally demagnetized. The heat radiation amount at the end surface 2a of the conductor 2 is designed to be larger than the heat generation amount.

  That is, by fixing the conductor 2 having higher conductivity than the permanent magnet 1 around the permanent magnet 1, the magnetic field fluctuation of the permanent magnet 1 is reduced to reduce the heat generation of the permanent magnet 1 and to the conductor 2 surrounding the permanent magnet 1. A material having a high thermal conductivity (a material having a higher thermal conductivity than the permanent magnet 1, the rotor core 6, and the magnet plate 10) is used. Furthermore, as an example of a design in which the end surface 2a of the conductor 2 having high conductivity and high thermal conductivity is increased, the heat radiation area is reduced by providing a fin structure on the end surface 2a of the conductor 2. Increase it.

  As described above, according to the permanent magnet type synchronous motor according to this embodiment, the conductor 2 having higher conductivity than the permanent magnet 1 is fixed around the permanent magnet 1 to reduce the magnetic field fluctuation of the permanent magnet 1 and become permanent. The heat generated by the permanent magnet 1 and the heat generated by the conductor 2 are reduced from the end surface 2a of the conductor 2 by reducing the heat generation of the magnet 1 and by making the conductor 2 surrounding the permanent magnet 1 a material having high thermal conductivity. Can be released to the outside.

It is a perspective view of the conductor which concerns on 1st Embodiment. It is a perspective view of the heat insulating material which concerns on 2nd Embodiment. It is a perspective view of the conductor formed with the conducting wire which concerns on 3rd Embodiment. It is a perspective view of the conductor which concerns on 4th Embodiment. 1 is a plan view of a permanent magnet type synchronous motor according to the present invention. It is the figure which showed the magnetic flux density in the time change of A point in FIG. It is the figure which showed the magnet eddy current loss when the circumference | surroundings of a permanent magnet are enclosed with a conductor, and when not enclosing with a conductor. It is the figure which showed the eddy current of the permanent magnet. It is a perspective view of the conventional permanent magnet type synchronous motor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Permanent magnet 2 Conductor 3 Thin plate 4 Heat insulating material 5 Conductor 6 Rotor core 7 Flux barrier 8 Stator core 9 Winding 10 Magnet plate

Claims (5)

In a permanent magnet type synchronous motor that holds a permanent magnet by a rotor core,
A permanent magnet type synchronous motor comprising a conductor having higher conductivity than the permanent magnet which surrounds the permanent magnet and reduces eddy current of the permanent magnet. The permanent magnet synchronous motor according to claim 1, further comprising a heat insulating material that covers a surface of the conductor to prevent heat of the conductor from being transmitted to the permanent magnet and the rotor core. 3. The permanent magnet according to claim 2, wherein the heat insulating material is not installed on a surface of the conductor end portion of the rotor core end portion so as to release heat of the conductor to the outside and suppress a temperature rise of the conductor. Type synchronous motor. The permanent magnet type synchronous motor according to claim 1, wherein the conductor is formed of a conductive wire. 2. The permanent magnet synchronization according to claim 1, wherein the conductor has higher thermal conductivity than the permanent magnet and the rotor core, and a heat dissipation amount on the surface of the conductor end is larger than a heat generation amount of the conductor. Electric motor.