JPH08103058A - Induction motor - Google Patents

Abstract

PURPOSE: To provide an induction motor which can generate high torque with simple and solid constitution. CONSTITUTION: A cylindrical rotor 34, where permanent magnets 36 are attached to the periphery, is arranged rotatably within a rotor 26. When the stator 22 is energized and a rotating magnetic field is generated by the action of the permanent magnet 36 of the cylindrical rotor 34, the cylindrical rotor 34 rotates, synchronizing with it. The magnetic flux generated in the stator 22 goes to the opposed permanent magnet 36, so it turns out that the magnetic flux crosses the rotor 26 in diametrical direction. That is, the magnetic flux crosses the rotor 26 in diametrical direction, so torque generated in the rotor 26 becomes large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction motor, and more particularly to an induction motor capable of generating high torque.

[0002]

2. Description of the Related Art Induction motors have been widely used in various industrial fields since they are robust, inexpensive and do not require speed control. In addition, when used at variable speeds, DC motors have been the mainstream in the past, but due to advances in power electronics elements and the development of control technologies such as vector control, it has become possible to operate induction motors at variable speeds. It is replacing the motor. The principle of this induction motor is that an electric current is caused to flow in a primary coil arranged in a stator to generate a magnetic flux, an induced current is generated on the rotor side by the magnetic flux, and a torque is generated by an interaction between the magnetic flux and the induced current. Is generated.

[0003]

In this induction motor, high torque is required in various fields, but a technique capable of generating high torque due to the structure of the motor itself has not been proposed so much. The main reason why the induction motor cannot generate high torque is that the magnetic flux generated by the stator bypasses (does not enter the inside of the rotor) and contributes to the torque in the radial direction of the rotor. The density is small.

The bypass of the magnetic flux will be described with reference to FIG. FIG. 10 shows a four-pole squirrel-cage induction motor, in which a stator 82 is provided with a winding 84, and a rotor 86 is provided.
Is provided with a car 88 including a plurality of secondary conductors 88a. The arrow A in the figure indicates the direction of rotation of the magnetic field generated by the stator 82. In the induction motor, the magnetic force lines 90 take a loop-shaped locus at each pole provided on the stator 82, and the radial component of the rotor 86 is small. Further, with reference to FIG. 11, a reduction in torque due to bypass of magnetic flux will be described. FIG. 11 (A)
FIG. 6 is a diagram showing generation of a speed electromotive force in one secondary conductor G of a plurality of secondary conductors 88 a that form a car 88 provided in the rotor 86. The secondary conductor G is the rotor 86.
With the rotation of, the magnetic flux B moves in the direction of arrow C at a speed v. The velocity electromotive force e in the secondary conductor G is a product of an effective magnetic flux component and velocity according to Fleming's right-hand rule. Here, the effective magnetic flux component is the component in the direction perpendicular to the moving direction (that is, the radial direction of the rotor), but here the magnetic flux is deflected from the radial direction by cos θ, so Bco
It becomes sθ. Therefore, the speed electromotive force e is (v × B cos θ)
L (where L represents the length of the secondary conductor G). That is, the speed electromotive force e is reduced by cos θ.

Further, the force F generated by the secondary conductor G will be described with reference to FIG. The current i flowing through the secondary conductor G is i = where R is the resistance of the secondary conductor.
It is represented by e / R. In addition, the force F generated in the secondary conductor G
Is the product of the magnetic flux B and the current i due to the speed electromotive force e according to Fleming's left-hand rule F = (i × B) L =
It is represented by [(v · B cos θ · L) / R] · B · L. Since this generated force F is generated in the direction perpendicular to the magnetic flux B,
The force on the secondary conductor G that rotates the rotor 86 is a cos θ component of this force F (tangential component to the rotor) F.
It becomes cos θ. Therefore, the force generated is [(v · B cos
θ · L) × B)] L · cos θ = v · B ² · L ² · cos ²
θ, which is the deflection angle of the magnetic flux in the radial direction, cosθ
It can be seen that it has decreased with the square of.

A rotor shown in FIG. 12 has been proposed as a structure for preventing the bypass of the magnetic flux and increasing the torque of the induction motor. The rotor 186 has a structure in which a laminated iron core 172 is attached to the shaft 170, and a copper rotor 176 having a large number of iron wires 174 radially embedded therein is provided around the laminated iron core 172. Magnetic flux is iron wire 1 with low magnetic resistance
Will be directed radially to penetrate 74,
The above-mentioned value of cos θ approaches “1” and the torque can be increased. However, since a large number of iron wires 174 have to be radially arranged on the copper rotor 176, there is a problem that the structure becomes complicated and the cost becomes high.

As another method for increasing the torque of the induction motor, a structure in which a stator is provided inside the rotor shown in FIG. 13 is IEEE TRANSACTIONS O.
NMAGNETICS, VOL. MAG-20,
NO. 5, SEPTEMBER 1984 No. 1786
~ Page 1788. In this induction motor,
Inside the outer stator 282A, the rotor 286 supported by the hollow shaft 270A is arranged.
An internal stator 282B is arranged inside 86. This internal stator 282B is fixed to the shaft 270B,
The rotor 286 is cantilevered by the bearing 272 with respect to the shaft 270B. A cooling fan 274 is provided around the hollow shaft 270A.

In the induction motor shown in FIG. 13, although the torque can be increased, the rotating force of the rotor 286 is applied to the hollow shaft 2.
Since the rotor 286 is cantilevered and taken out via 70A, the structure is complicated and it is difficult to manufacture. In addition, it is necessary to pass the electric wire for the internal stator 282B into the shaft 270B, which makes wiring difficult. . When the present inventor conducted magnetic field analysis of the structure of this induction motor, in order to generate a high torque, an external stator 282A and an internal stator 282B were found to be generated.
Then, it was found that it is necessary to generate magnetic flux of equal strength. However, for this purpose the external stator 28
2A must be thin (the amount of winding is small) and the radius of the internal stator 282B must be large (the amount of winding is large). That is, since the winding amount of the external stator 282A corresponding to the stator of the conventional induction motor has to be reduced, the torque cannot be greatly improved as compared with the conventional induction motor. Further, although the fan 274 is provided, cooling of the internal stator 282B poses a problem.
Further, the induction motor is a motor in which one motor including the rotor 286 provided outside the inner stator 282B and one motor including the rotor 286 provided inside the outer stator 282A are combined. It can be considered that, while this structure can improve the torque,
The efficiency is considerably lower than that of the conventional induction motor. Due to these problems, research and proposal for practical use of the induction motor shown in FIG. 13 have not been continued.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an induction motor capable of generating high torque with a simple and robust structure.

[0010]

In order to achieve the above-mentioned object, in the present invention, a stator 22 for generating a rotating magnetic field and a shaft 3 are provided.
An induction motor 20 comprising a rotor 26 fixed to 2 and rotating in the stator 22, the induction motor 20 being made of a material having a low magnetic resistance and disposed in a hollow space formed in the rotor 26. A magnet 36 is attached so as to face the rotating magnetic field of the stator 22, and a cylindrical member 34 rotatably supported by the shaft 32 is provided.

[0011]

In the induction motor 20 configured as described above,
Since the magnet 36 is attached to the surface of the tubular member 34 so as to face the rotating magnetic field of the stator 22, the stator 22
Is excited and a rotating magnetic field is generated, the cylindrical member 34 rotates in synchronization with this. Since the magnetic flux generated in the stator 22 is directed to the facing magnet 36, it crosses the rotor 26 in the radial direction. That is, since the magnetic flux crosses the rotor 26 in the radial direction, the torque generated in the rotor 26 increases.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment 40 of the present invention.
The configuration of a 0 W three-phase four-pole cage induction motor 20 is shown. Here, FIG. 1A shows a vertical section and FIG. 1B shows a horizontal section. A plurality of slots 2 are formed on the inner circumference of the stator 22.
4 are provided, and the winding wire 23 is arranged in each slot 24. The stator 22 used is the same as that of a conventional squirrel cage induction motor, and a pair of bearings 30, 30 are attached to the substantially central portion thereof to rotatably support a shaft 32. A rotor 26 incorporating a car is fixed to the shaft 32. The car is composed of a pair of short-circuit rings 28b (only one of which is shown in FIG. 1B) and a plurality of secondary conductors 28a, as in the case of the conventional car induction motor. Inside the rotor 26, a steel cylindrical rotor 34 is arranged,
The cylindrical rotor 34 is rotatably supported by the shaft 32 by a pair of bearings 38, 38. Four permanent magnets 36 are attached to the outer periphery of the cylindrical rotor 34 in correspondence with the number of poles (fields) of the squirrel cage induction motor 20. The permanent magnet 36 is composed of a neodymium-iron-boron magnet. Although not shown, a stator frame is provided on the outer periphery of the stator 22.

Next, the operation of the squirrel cage induction motor 20 will be described with reference to FIG. Winding 23 of the stator 22
When a three-phase alternating current is applied to, a rotating magnetic field is generated in the direction of arrow A in the figure. The magnetic flux of the rotating magnetic field crosses each of the secondary conductors 28a of the rotor 26, whereby velocity electromotive force is generated in the secondary conductor 28a, and the velocity electromotive force causes a current to flow in the secondary conductor 28a. A torque is generated by the interaction between the electric current and the magnetic flux to rotate the rotor 26 in the same direction as the magnetic field. This rotation speed has a slip in relation to the generated torque and is lower than the speed of the rotating magnetic field on the stator 22 side.
On the other hand, since the permanent magnets 36 are attracted to the magnetic force generated on the stator side, the cylindrical rotor 34 rotates in perfect synchronization with the rotating magnetic field generated on the stator 22 (to be exact, a slight angle). Have a delay). This basket type induction motor 2
At 0, since the magnetic flux is directed to the opposing permanent magnet 36, it crosses the secondary conductor 28a of the rotor 26 in the radial direction. That is, since the magnetic flux crosses the secondary conductor 28a in the radial direction, the torque generated in the rotor 26 increases.

The principle of this torque generation will be described in more detail with reference to FIG. As shown in FIG.
The magnetic force lines 90 from the winding wire 23 are directed toward the facing permanent magnet 36 side, and the magnetic force lines 90 from the permanent magnet 36 are directed toward the facing winding 23 side. That is, the magnetic flux is directed in the radial direction of the rotor 26. Therefore, the speed electromotive force e in one secondary conductor H moving relatively at the speed v with respect to the magnetic flux B in the direction of arrow C with the rotation of the rotating magnetic field is
According to Fleming's right-hand rule, it is the product of the effective magnetic flux component and velocity. Here, the effective magnetic flux component is a component in the direction perpendicular to the relative movement direction C (that is, the radial direction of the rotor), but here, since the magnetic flux is directed in the radial direction, all the magnetic flux B Will work effectively. Therefore, the velocity electromotive force e is represented by vBL (where L represents the length of the secondary conductor H).

Further, the force F generated by the secondary conductor H will be described with reference to FIG. The current i flowing through the secondary conductor H is i = e, where R is the resistance of the secondary conductor H.
It is represented by / R. Further, the force F generated by the interaction between the current and the magnetic flux in the secondary conductor H is the product of the magnetic flux B and the current i due to the speed electromotive force e according to Fleming's left-hand rule, and F = (i × B) It is represented by L =. This force F is
The direction perpendicular to the radial magnetic flux B (that is, the rotor 2
6 occurs in the tangential direction (6), and therefore occurs in the direction in which the rotor 26 is rotated. Therefore, all the forces generated by the respective secondary conductors are effectively used as the torque of the rotor 26.

Now, the result of calculating the magnetic flux density (T) in the radial direction generated in the squirrel cage induction motor 20 by magnetic field analysis will be described with reference to the graph of FIG. The dotted line in the graph is that of a conventional squirrel cage induction motor, and the solid line is the first
In the example, the horizontal axis represents electrical angle (rad).
The vertical axis represents the magnetic flux density (T) in the radial direction. Here, the conventional squirrel-cage induction motor to be compared has a stator, a winding and a cage of the same standard as the squirrel-cage induction motor 20 of the first embodiment. On the other hand, the first embodiment differs from the first embodiment in that the cylindrical rotor 34 to which the permanent magnet 36 is fixed is arranged in the rotor 26 as described above with reference to FIG. In the figure, a valley of magnetic flux density (magnetic flux density 0) is a portion where passage of magnetic flux is blocked by a cage having low magnetic permeability. In the conventional cage type induction motor,
While the magnetic flux changes sinusoidally with respect to the electrical angle, in the squirrel-cage induction motor 20 of the first embodiment, it rises in a rectangular wave shape, that is, steeply rises in the vicinity of the electrical angle π / 4. Please note that you are down. As can be seen from this graph, the cage induction motor 2 of the first embodiment
At 0, the magnetic flux density (T) is improved over the conventional type over all electrical angles. Although the increase in the magnetic flux density is not large, the torque is greatly increased because it is proportional to the square of the magnetic flux density in the radial direction.

The results of two-dimensional magnetic field analysis of the squirrel cage induction motor 20 of the first embodiment and the conventional squirrel cage induction motor using a finite integral equation program will be described with reference to FIG. To do. Here, FIG. 5A shows the lines of magnetic force in the conventional squirrel cage induction motor, and FIG.
(B) shows magnetic lines of force in the squirrel cage induction motor 20 of the first embodiment. As can be seen from FIG. 5 (A), in the conventional squirrel-cage induction motor, the lines of magnetic force bypass and do not go in the radial direction of the rotor, whereas from FIG.
In the squirrel cage induction motor 20 of the embodiment, it can be seen that the magnetic force lines are directed in the radial direction of the rotor. In this way, the result of the magnetic field analysis also demonstrates the improvement in torque described above with reference to FIG.

Further, the torque generated by the squirrel cage induction motor 20 of the first embodiment will be described with reference to FIG. The dotted line in the graph shows that of the conventional squirrel-cage induction motor, the solid line shows that of the squirrel-cage induction motor 20 of the first embodiment, the horizontal axis represents the rotational speed (rpm), and the vertical axis represents the torque ( N · m). Here, the torque generated when the load was increased on the induction motor from a rotation speed of almost zero slip (1800 rpm) to increase the slip and decrease the rotation speed was measured. Whereas the conventional squirrel-cage induction motor has a maximum torque (stopping torque) of 6.4 N · m between 900 and 1100 rpm, the squirrel-cage induction motor 20 of the first embodiment uses 900 rpm. 7.6
N ・ m is generated and the torque is improved by about 19%.

Next, the power factor of the squirrel cage induction motor 20 of the first embodiment will be described. FIG. 7 is a line voltage-power factor characteristic diagram measured by mounting a load such as a torque detector on the squirrel cage induction motor 20. As is clear from this figure, in the case of the first embodiment (with magnet), the operation can be performed at the power factor angle (ψ) = 0, that is, cosψ = 1. From now on, the conventional induction motor 20 has a power factor (cos
ψ = 0.75 to 0.85), while cos ψ = 1
It is possible to operate at a power factor of 100%.

Further, as is apparent from FIG. 7, the power factor angle of the conventional type is limited to within the delay power factor. However, in this embodiment, the power factor angle extends from the delayed power factor to the advanced power factor. As a result, the squirrel cage induction motor of this embodiment can be operated at any power factor.

Next, a second embodiment of the present invention will be described. In the first embodiment, the cylindrical rotor 34 having the permanent magnet 36 attached is arranged inside the squirrel-cage induction motor, but in the second embodiment, the solid rotor induction motor has the cylindrical rotor of the first embodiment. The rotor 34 is arranged. The mechanical structure of the solid rotor induction motor of the second embodiment is the same as that of the first embodiment described above with reference to FIG. In this solid rotor type induction motor, a lump iron core rotor (however, a hollow portion for housing the cylindrical rotor 34 is formed) having no cage or winding is used for the rotor. This solid rotor type induction motor has no cogging torque and has a large starting torque and a drooping characteristic.

The results of analyzing the radial magnetic flux density (T) generated in the solid rotor type induction motor according to the second embodiment will be described with reference to the graph of FIG. The dotted line in the graph shows that of the conventional solid rotor induction motor, the solid line shows that of the second embodiment, the horizontal axis shows the electrical angle (rad), and the vertical axis shows the radial magnetic flux density (T ) Is represented. Here, the conventional solid rotor type induction motor to be compared has a stator and windings of the same standard as the solid rotor type induction motor of the second embodiment, but the rotor is formed of a solid iron core. There is. On the contrary,
In the second embodiment, as described above, the cylindrical rotor having the permanent magnet fixed therein is arranged in the rotor. In the conventional solid rotor type induction motor, the magnetic flux changes sinusoidally with respect to the electrical angle, whereas in the solid rotor type induction motor of the second embodiment, it has a rectangular wave shape.
That is, it should be noted that it rises sharply in the vicinity of the electrical angle π / 4. As can be seen from this graph, in the solid rotor induction motor of the first embodiment, the magnetic flux density (T) is greatly improved over the conventional one over the entire electrical angle.

The results of the two-dimensional magnetic field analysis of the solid rotor type induction motor of the first embodiment and the conventional solid rotor type induction motor will now be described with reference to FIG. Here, FIG. 9A shows the magnetic force lines in the conventional solid rotor type induction motor, and FIG. 9B shows the magnetic force lines in the solid rotor type induction motor of the second embodiment. As can be seen from FIG. 9 (A), in the conventional solid rotor type induction motor, the lines of magnetic force bypass and do not go in the radial direction of the rotor, while from FIG. 9 (B) the solid rotor of the second embodiment. In the induction motor, it can be seen that the magnetic field lines are directed in the radial direction of the rotor.

From the magnetic field analysis of the squirrel cage induction motor 20 of the first embodiment with reference to FIG. 5, it is theoretically calculated that the torque is improved by 25% (the square of the magnetic flux density in the radial direction is calculated around the rotor). As a result of measurement as described above with reference to FIG. 6, it was possible to actually achieve a torque improvement of 19%. That is, it was proved that high torque can be obtained by adjusting the direction of the magnetic flux in the radial direction by the permanent magnet 36. Further, in the solid rotor type induction motor of the second embodiment, as a result of the magnetic field analysis shown in FIG. 8, it was calculated that the torque could be improved by 75%. That is, in the first embodiment, since the magnetic flux is regulated by the car because it is a squirrel-cage induction motor, the effect of the permanent magnet 36 is not relatively large, but in the solid-rotor induction motor in which the flow of the magnetic flux easily bypasses. It is expected that a great effect will be obtained. Measurement of this solid rotor type induction motor with an actual machine has not been completed, but it is estimated that a considerably high value can be obtained. Further, in the first and second embodiments, unlike the prior art described above with reference to FIG. 13, the permanent magnet 36 that does not consume energy is simply rotated with the rotating magnetic field of the stator. Since there is almost no loss, it is possible to improve not only the torque but also the efficiency of the induction motor.

In the conventional control method such as vector control of the induction motor, since the control system is constructed by performing the analysis based on the assumption that the magnetic flux density and the direction of the magnetic flux are constant, the magnetic flux of the rotor, etc. Due to changes, there were often situations where the induction motor could not be controlled precisely. On the other hand, in the induction motors of the first and second embodiments, the magnetic flux density and the direction of the magnetic flux of the rotor are always constant, and the analysis for vector control can be performed easily and accurately. It becomes possible to control the electric motor.

In the structure of the squirrel cage induction motor 20 of the first embodiment described above with reference to FIG. 1, the cylindrical rotor 3 is used.
Although a member made of iron is used for 4, it is also possible to use nickel or the like as long as it is a material capable of favorably transmitting magnetic flux. Further, in the configuration of the cylindrical rotor 34 shown in FIG. 1, a hollow portion is provided between the shaft 32 and the shaft 32, but it is also possible to further thicken the wall pressure and configure the portion other than the shaft 32 with iron. is there. On the contrary, it is possible to further reduce the wall pressure, but if the wall pressure is made too thin, it becomes difficult for the magnetic flux to pass. Therefore, the wall pressure is required to allow the magnetic flux to pass through.

[0027]

As described above, according to the induction motor of the present invention, since the magnetic flux generated in the stator is directed to the facing magnet, it crosses the rotor in the radial direction. That is,
Since the magnetic flux crosses the rotor in the radial direction, the torque generated in the rotor, that is, the torque of the induction motor increases. Further, in the induction motor of the present invention, since it is possible to improve the torque with a simple configuration in which the cylindrical member having the magnet attached to the outer periphery so as to face the rotating magnetic field of the stator is arranged in the rotor, It can be constructed inexpensively and robustly. Therefore, it is possible to increase the torque while making the most of the characteristics of the induction motor that are inexpensive and robust.

[Brief description of drawings]

1 is a longitudinal sectional view and a lateral sectional view of a squirrel cage induction motor according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a rotation principle of the squirrel cage induction motor of the first embodiment.

FIG. 3 is an explanatory diagram of speed electromotive force and generated torque of the squirrel cage induction motor of the first embodiment.

FIG. 4 is a graph showing the magnetic flux density in the radial direction of the squirrel cage induction motor according to the first embodiment.

FIG. 5 is an analysis diagram of magnetic field analysis of the squirrel cage induction motor according to the first embodiment.

FIG. 6 is a graph showing torque characteristics of the squirrel cage induction motor of the first embodiment.

FIG. 7 is a graph showing line voltage-power factor characteristics of the squirrel cage induction motor of the first embodiment.

FIG. 8 is a graph showing the magnetic flux density in the radial direction of the solid rotor induction motor of the second embodiment.

FIG. 9 is an analysis diagram of a magnetic field analysis of a solid rotor induction motor according to a second embodiment.

FIG. 10 is an explanatory diagram showing a rotation principle of the induction motor.

FIG. 11 is an explanatory diagram of speed electromotive force and generated torque of a squirrel-cage induction motor according to a conventional technique.

FIG. 12 is a perspective view of a rotor of a conventional induction motor proposed for improving torque.

FIG. 13 is a configuration diagram of a conventional induction motor proposed for improving torque.

[Explanation of symbols]

 20 Cage Induction Motor 22 Stator 26 Rotor 28a Secondary Conductor 34 Cylindrical Rotor 36 Permanent Magnet

Claims (2)

[Claims] 1. An induction motor comprising a stator that generates a rotating magnetic field and a rotor that is fixed to a shaft and rotates within the stator, the induction motor being disposed in a hollow space formed in the rotor. An induction motor comprising a tubular member made of a material having a low magnetic resistance, the magnet being attached to the outer periphery so as to face the rotating magnetic field of the stator, and the shaft being rotatably supported by the shaft. 2. The induction motor according to claim 1, wherein the number of magnets attached to the outer circumference of the tubular member is equal to the number of poles of the induction motor.