JP2919499B2 - Variable speed induction motor - Google Patents

Description

The present invention has a single rotor and a plurality of stators,
Variable speed induction that can rotate the arbitrary stator to generate a phase difference in the voltage induced in the rotor conductor portion facing the stator and arbitrarily change the rotational speed and generated torque of the rotor. The present invention relates to a control device for electric motor acceleration control.

[Conventional technology]

For example, according to the related art, the control device and method of the operating speed of an electric cargo handling machine or the like include an inverter, a pole number switch, a voltage control, and the like, and a mechanical transmission.
In addition, a device has been devised to use these devices / methods in a combined manner to reduce the shake or shock caused by a change in the speed of the transport / movement of the transported / moved / lifted load.

The speed of the constant-speed traveling / moving can be controlled by the above-described conventional technology, but it is difficult to control the acceleration in the acceleration range from the constant-speed traveling or from the constant-speed traveling to the stop, In order to perform control until reaching an arbitrary speed, expensive equipment is required.

[Problems to be solved by the invention]

Such acceleration control includes positive and negative acceleration. Of these, negative acceleration is called braking, and many methods can be used electrically. For example, there are antiphase braking, DC braking, power generation braking, and unbalanced braking.

There is Japanese Patent Publication No. 63-34709 concerning reverse phase braking,
Applying an output of a second phase sequence opposite to the first phase sequence to the three-phase AC motor, in which both the frequency and the voltage have been reduced from the maximum values during the operation in the first phase sequence by the inverter, It brakes. These require an inverter device suitable for the motor.

In addition, both dynamic braking and unbalanced braking require that the control circuit for braking becomes expensive,
It is necessary to use differently according to the size and frequency of GD ² . For example, in addition to the above-described reverse-phase braking, DC braking is suitable for braking of a hoist for a long time, condenser braking is mainly suitable for braking at a relatively high speed such as a ropeway, and single-phase braking is suitable for soft braking because the braking torque is relatively small. This is what is known from the prior art.

According to the above-described prior art, each electric braking method exhibits a unique braking torque characteristic and its characteristic curve is uniquely determined. Therefore, its use range and equipment used are limited by each braking method. Also, each braking device is an expensive device using an inverter, a large-capacity element (thyristor), or the like.

In view of the above, it is an object of the present invention to provide a variable-speed induction motor that can be used for equipment having various load characteristics with the same braking device, has a simple structure, and can be manufactured at low cost, and a braking device for the variable-speed induction motor. It is.

[Means for solving the problem]

The present invention relates to a rotating apparatus having two rotor cores which are mounted on the same rotating shaft with an arbitrary gap therebetween, and a plurality of conductors communicating with the two rotor cores are integrally formed. And two stator cores are arranged side by side to face the two rotor cores, respectively, and the windings wound on the stator cores are two stators connected in series with each other. And a connecting member for mutually short-circuiting the plurality of conductors at an arbitrary interval between the two rotor cores, wherein at least one of the two stators is a rotor. In a variable speed induction motor formed on a concentrically rotating rotating stator, a control device for controlling a rotating drive device for rotating the stator is provided with a reverse phase for switching the direction of the rotating magnetic field of the stator in the opposite direction. The device is connected to a Y-Δ switching device for switching the stator winding Y-Δ. In order to solve the above problem, the Y-Δ switching device is changed from the Δ connection to the Y connection during the anti-phase braking operation of the anti-phase device, and the two stators are provided with the voltage adjusting devices. Means.

Further, according to the present invention, in the variable speed induction motor, a switching device that is connected to a power supply during operation, supplies power, and short-circuits a winding terminal during braking is provided in one stator winding, and is connected in normal phase during operation. The means for solving the above problem is provided by providing the other stator winding with a reverse phase device connected in reverse phase during braking.

(Operation)

The variable speed induction motor of the present invention changes the rotation speed and generated torque of the rotor by the phase difference between the stators by providing the phase difference of the rotating magnetic field between the stators by the rotation of the rotating stator. It becomes possible. When braking is performed on the variable speed induction motor by the reverse phase device, if a phase difference is provided, the braking torque changes according to the phase difference, and various braking torque characteristics can be generated. In addition to the method in which the stator is connected to the power supply with the Δ connection and the operation is switched to the reverse-phase braking as it is, when the connection is switched to the Y connection and the reverse-phase braking is switched, the braking force is Δ due to the line voltage difference of the Y connection. Soft braking force lower than that at the time of connection can be obtained. Furthermore,
The braking force can be controlled by the phase difference caused by the rotation. For example, when a braking force lower than the braking force in the range of the phase difference (electrical angle 0 ° to 180 °) is required, the supply voltage to the stator is decreased. As a result, the braking force can be kept low.

Also, if one of the stator windings is short-circuited during control and an opposite-phase rotating magnetic field is applied to the other stator winding, the other stator performs anti-phase braking on the other rotor core,
The current induced in the rotor conductor by the opposite-phase rotating magnetic field induces a voltage in the opposed short-circuited stator winding by the rotation of one of the rotor cores and causes a current to flow.
On the one hand, it is configured to perform anti-phase braking and on the other hand to perform dynamic braking.

Also in this case, the braking torque can be variously changed by the rotation of the rotating stator. The braking torque can also be changed by providing a variable resistor at the short-circuit point of one stator winding.

From the above, the rotation of the rotation stator, the reverse phase device,
By a Y-Δ switching device and a voltage regulator, or
A switching device for shorting one stator winding, the GD ² in the same load with reverse phase power by a reverse-phase device for supplying to the other stator winding may correspond to those of all load torque or GD ² It has become possible to provide a variable speed induction motor that can cope with changes at a low cost by the simplest method.

Further, the rotation of the stator by the stator rotation means is effective both in increasing the speed and in braking, and various torque characteristic curves and braking torque curves can be obtained by the rotation.

〔Example〕

Although the present invention will be described in detail mainly with reference to a two-stator induction motor having a cage rotor, it goes without saying that the present invention is not limited to this. Further, as described above, there may be a plurality of induction motors having a winding type rotor, and in some cases, the torque characteristics may be further diversified by switching the star winding and the delta wiring of the stator winding in combination. . The configuration between the rotor cores may also use a space, a non-magnetic material, a magnetic material, or the like.

The applicant has already described in detail, as Japanese Patent Application No. 61-128314, the configuration and operation of an induction motor including a plurality of stators, which are a part of the configuration of the present invention. This will be described with reference to FIGS.

Referring to FIG. 1, one embodiment of an electric motor which forms a part of the configuration of the present invention will be described. Reference numeral 1 denotes a variable speed induction motor according to the present invention, and the induction motor 1 has the following configuration. The rotor cores 2 and 3 made of a magnetic material are mounted on the rotor shaft 4 at arbitrary intervals. A non-magnetic core 5 is provided between the rotor cores 2 and 3, or a space is provided between the rotor cores 2 and 3. Rotor core
Each of the plurality of conductors 6 provided in each of the plurality of conductors 6 is connected to and connected to the rotor cores 2 and 3 to form an integral rotor 7. Both ends are short-circuit rings 8,
Shorted by 8. In this embodiment, the conductors 6 provided on the rotor 7 are connected to the non-magnetic core 5 between the rotor cores 2 and 3 so that each of the conductors 6. They are connected via a material 9.

A first stator 12 and a second stator 13 having windings 10 and 11 provided on outer portions facing the rotating cores 2 and 3 are arranged side by side on a machine frame 14. Equipped with a sliding bearing 15 and the second stator
13 is fixed to the machine frame 14. Here, the stator rotating device will be described. A gear 17 is fitted on one peripheral surface of the first stator 12. A driving gear 21 is mounted on a rotating electric motor 20 fixedly mounted on the outer periphery of the machine frame 14, and the driving gear 21 is connected to the first stator 12.
The gear 17 is engaged with the gear 17. With such a configuration, the first stator 12 constitutes the rotation rotation stator 16 concentrically with the rotor 7 by the operation of the rotation motor 20.
Thus, the rotation of the first stator 12 and the second stator 13 constitute a voltage phase shifter.

A speed detector 22 is associated with the rotor shaft 4 of the rotor 7. In this case, either a non-contact type or a contact type may be used.

The connection between the windings 10 and 11 of the first stator 12 and the second stator 13 is operated by Δ connection, and braking is performed by Y connection.

Next, a first embodiment of the present invention is shown in FIG. The induction motor 1 is connected to the power supply 30 via a power switch 31, a reverse phase device 43 and a Y-Δ switching device 44. Further, the power supply 30 is connected to a control device 34 including a control unit 32 and an operation process storage unit 33. The control unit 32 includes the power switchgear 31, the reverse phase device 43, the Y-Δ switching device 44, and the speed The detector 22 and the stator rotating device 35 are connected.

Further, the control unit 32 will be described. FIG. 3 shows a block diagram thereof. According to the block diagram, the signal input means 40 for inputting the signal of the speed detector 22 every minute time, the arithmetic means 37 for arithmetically processing the speed signal of the input means 40, and the operation of the arithmetic means 37 via the result and the control means 41 Comparison means 38 for comparing with operation process data sent from process storage unit 33
And a signal output means 39 for outputting a positive or negative rotation signal to the rotation device 35 according to the result of the comparison means 38, and a control means 41 for controlling these. By the way, the control means
41 is to be implemented by current technology means such as a microcomputer configuration using a microprocessor.

The power switchgear 31, the reverse phase device 43 and the Y-Δ switching device 44 are controlled by the control means 41 via the signal output means 39. The signal input means 40 may receive an external input signal 42 such as an external position sensor, for example, an automatic warehouse stop position sensor.

Next, FIG. 4 shows the operation process stored in the operation process storage unit 33. The operation process is any rated speed and V _1, there the time from the start up to the rated speed as T _1. This gives an acceleration. V ₂ is a low speed immediately before reaching the arbitrary stopping position, there the time to decelerate from the speed V ₁ to V ₂ as T _2. Incidentally, the timing of deceleration is an external signal from an external position sensor by an operation of an operator or the like, and the same applies to the stop.

FIG. 5 is an example of a torque characteristic curve of the induction motor according to the present invention, and shows a part of a change in the torque curve when the rotating stator is rotated from 0 ° to 180 ° (electrical angle). ing.

Next, the connection of the stator windings 10 and 11 will be described with reference to FIG. 6, and the changeover switch for switching the connection between the reverse phase device 43 and the Y-Δ switching device 44 will be described with reference to FIG. 6 and FIG.

FIG. 6 shows the connection of the stator windings 10 and 11,
In parallel connection, it is possible to switch to both Y connection and Δ connection. M ₁ and M ₂ is switched to the Y-connection and Δ-connected by alternate opening and closing of the two switches in conjunction a switch.
The opening and closing of M ₃ are those for switching the rotation direction of the rotating magnetic field of the two stator parallel connection, the forward and reverse rotation by alternately opening and closing of two switches. In the state shown in FIG. 6, the switches M ₁ , M ₂ , and M ₃ are switched in the forward direction with parallel Δ connection. (M ₁₁
= Closed, M ₁₂ = Open, M ₂₁ = closed, M ₂₂ = Open, M ₃₁ = closed, M ₃₂ = open).

FIG. 7 shows a simple sequence circuit acting on the switching of the switches M ₁ , M ₂ , M ₃ .

Reverse phase device 43 Yes to relay 46 which operates on the output signal of the coil 45 and the signal output means 39 for operating the switch M ₃ is provided,
It is constituted by switch M ₃ and the coil 45 and the relay 46.

Then Y-delta switching device 44 is Yes and relay 48 which operates on the output signal of the switch M _1, coils 47, 49 to operate the M ₂ and the signal output unit 39 is provided, switches M ₁ and the coil 47, the coil It consists of 49 and relay 48. In the state shown in FIG. 7, the relays 46 and 48 are both OFF, and the coils 45, 47 and
49 Not applied.

Next, braking will be described. When the direction of rotation of the induction motor in connection FIG. 6 and the forward rotation switch the M ₃ (M
₃₁ = open, M ₃₂ = closed) and a rotating magnetic field in the reverse rotation direction, and has a braking action against forward rotation.

When the switches M ₁ and M ₂ are switched at the same time as M ₃ , the stator windings are connected in a Y-connection, so that soft braking is performed as compared with the Δ-connection, and braking with less shock can be performed. When the rotation stator 16 is rotated when this braking action is generated,
The braking torque changes in accordance with an arbitrary rotation angle. FIG. 8 shows the braking torque characteristics at this time. FIG. 8 shows the anti-phase braking torque in the Y connection according to the present invention. This braking torque is applied to the rotating stator as shown in FIG.
16 (the figures in the drawing electrical angle) rotation angle different each braking torque at any rotation angle by changing the variation of the load, but also respond to changes of GD ^2.

In addition, the braking torque curve changes to a right-up trend or a right-down trend depending on the type of the rotor, which is a high-resistance type or a low-resistance type.

In the present embodiment, as described above, the Y-connection (braking torque in FIG. 8) is used for braking. However, the present invention is not limited to this embodiment, and various combinations can be realized depending on the application by using a low-resistance type.

The operation of the above configuration will be described. When a start signal is externally input to the control means 41 from the signal input means 40, the control means 41 closes the power switch 31 via the signal output means 39. At this time, the rotation angle (electric angle) of the motor is located on the side where the phase difference is large, for example, 180 °.

The signal sent from the speed detector 22 is input to the signal input means 40.
Is input to the calculation means 37 via the. The arithmetic processing means 37 sends the speed change in the minute time Δt to the comparing means 38 as acceleration. The comparing means 38 compares the acceleration value up to the rated speed given from the operating process storage section 33. For example, the signal output means 39 outputs a positive signal if the acceleration is low, and a 0 or a negative signal if the acceleration is high. Output to the rotation device 35. Further, since the rotation speed at an arbitrary time is given from the operation process, the acceleration and both the rotation speed at that time are compared by the value of the speed detector 22 and the operation process storage unit, and from the comparison between the two. and the signal output to the stator pivot means, are intended to be accelerated stable up to rated speed V ₁ in the time T _1. In this way, the speed value with the speed detector 22 is compared with an arbitrary value stored in the operation process storage unit 33 or a predetermined acceleration, and the resulting difference causes the rotating stator to rotate. The motor rotates to change the torque characteristics in various ways, and gradually changes to a high-speed region with a torque characteristic larger than the load torque, that is, gradually changes the phase difference from 180 ° to 0 ° in the high-speed region. In addition, at the constant speed rotation, the intersection of the load torque and the torque characteristic of the electric motor is controlled so as to become the target rotation speed, and the rotation stator position is set.

Next, when deceleration is reached, when an external signal or the like by a stop sensor or an operation of an operator is input from the signal input means 40, the control means 41 transmits the signal through the signal output means 39 to the reverse phase device 43, the Y-Δ switching device. A signal is output to 44 to operate the relays 46 and 48 to apply the voltage to the coils 45, 47 and 49. Coil 45 and switch M ₁ and the switch M ₂ and switch M ₃ by application to the coil 47 and the coil 49 is operated, is switched from the Δ connection to Y-connection, also the direction of the rotating magnetic field is reverse direction. (M ₁₁ = open, M ₁₂ = closed, M ₂₁ = open, M ₂₂ = closed, M ₃₁ = open,
M ₃₂ = closed).

Since the rotating magnetic field is in the opposite direction, the induction motor 1 has a braking action.

At this time, the rotation angle (electric angle) of the motor is located on the side where the phase difference is small, for example, 0 °. Further, according to FIG. 8, the braking torque generates a braking torque having a phase difference (electric angle) of 0 °.

The signal sent from the speed detector 22 is input to the signal input means 40.
Is input to the calculation means 37 via the. The arithmetic processing means 37 sets the speed change in the minute time Δt as a negative acceleration
Send to 38. Comparison means 38 performs a comparison between the negative acceleration values up to the rated speed V ₂ imparted from the operation step storing unit 33, for example, positive if negative acceleration is small, the zero or negative signal if the acceleration Univ The signal is output from the signal output means 39 to the stator rotating device 35. Further, since the rotation speed at an arbitrary elapsed time is given from the operation process, both the negative acceleration and the rotation speed at that time are compared by the value of the speed detector 22 and the operation process storage unit, and the two values are compared. compared to the signal output to the stator rotating means from the one in which is accelerated stable up to rated speed V ₂ in the T ₂ hours. In this way, the speed value of the speed detector 22 is compared with a value at a given time or a predetermined acceleration stored in the operation process storage unit 33, and the resulting difference causes the rotating stator to move to the stator. By rotating with a rotating device, the torque characteristics are variously changed, and gradually shifted to a low speed region by the braking torque characteristics of the Y connection.

Speed performs braking as below reaches the V _2, the intersection between the torque characteristic of the load torque and the motor is controlled so as to be rotational velocity V ₂ that target. This control can either vary due to the inertia force of the load is controlled small braking torque by the inertia force of the load, or, in the normal rotation direction or switches the switch M ₂ is to hold the velocity V _2. Finally, when the stop operation of the stop position sensor or the operator is input from the signal input means 40, the control means 41 outputs a signal to the power supply opening / closing device 31 from the signal output means 39 to open the power supply and at the same time by any mechanical braking device. It is to stop.

As described above, according to the present invention, the two stator windings are connected in parallel to the power supply, and are switched to the Δ connection during operation and to the Y connection during braking, so that the two stator windings rotate in reverse rotation. In this case, the reverse phase switching is performed so as to give the braking force.

The braking torque is controlled by the rotation of the rotating stator,
When the rotation of the rotating stator requires a braking torque smaller than the braking torque when the electrical angle is set to 180 ° in FIG. 8, the present invention uses a voltage regulator. Since the driving torque is proportional to the square of the voltage, it also acts on the braking torque,
Even if the braking torque is out of the control range due to the rotation of the rotating stator, the control range can be further expanded by adjusting the voltage.

Next, a second embodiment will be described with reference to FIGS. 9 and 10. FIG. In this method, one of the stators performs dynamic braking and the other stator performs reverse-phase braking, and either the fixed stator or the rotating stator may be used.

FIG. 9 shows a connection diagram of the second embodiment. In parallel connection, M ₄ , M ₅ , M ₆ , and M ₇ are switches. Performs switching to reverse phase closing of M _4, in the opening and closing of M _5, the switching of Y-delta, in the opening and closing of M ₆ and M _7, in which switching between the short and the feed of delta to connection of the windings is there. The state shown in FIG. 9 shows a state in which both stators are connected to a three-phase power supply in parallel Δ connection. (M
₄₁ = Closed, M ₄₂ = Open, M ₅₁ = Closed, M ₅₂ = Open, M ₆₁ = Closed, M ₆₂ = Open, M ₇₁
= Closed, M ₇₂ = open) as shown in FIG. 10 is a simple sequence circuit acting on the switch _{M 1, M 2, M 3} , M 4.

Here reverse phase device 43 is provided with a relay 52 which operates on the output signal of the coil 50 and the signal output means 39 for operating the switch M ₄ is constituted by a switch M ₄ and the coil 50 and the relay 52 I have.

Then Y-delta switching device 44 is a coil for operating the switch M ₅
51 and a relay 53 which operates on the output signal of the signal output unit 39 is provided with, constituted by a switch M ₅ and the coil 51 and the relay 53. Finally, reference numeral 60 denotes a switching device for dynamic braking, which is provided with coils 54 and 56 for operating the switches M ₆ and M ₇ and a relay 66 which is operated by the output signal of the signal output means 39. The switches M ₆ and M ₇ , the coils 54 and 56, and the relay 55 constitute the switching device 60.

By the way, if a resistance device is provided on the short-circuit side of the switch M6, it is possible to control the dynamic braking and to obtain a wider braking range.

Next, braking of the present embodiment will be described. When the connection shown in FIG.
When 2,53,55 signal output to switch the switch M ₄ ~M _5, one of the stator windings by the switch M ₄ becomes reverse phase, switch M ₅
Is connected in a Y-connection. Further, the switching of the switches M ₆ and M ₇ causes the other stator winding to short-circuit the power supply terminal while maintaining the Δ connection, so that the rotation of the rotor generates an electromotive force. The generated electromotive force is consumed by the conductor resistance of the short-circuited stator winding and the like. FIG. 11 shows the braking torque at this time. Braking torque by the rotation of the first embodiment as well as rotating stator as this figure is changing, further by providing a resistance device to short side of the switch M ₆ of the present embodiment as described above A wide range of braking torque characteristics can be obtained.

As described above, the braking according to the present invention enables the braking torque uniquely determined by the braking device / method to be varied in various ways in accordance with load fluctuations or load changes, and is used as a braking device for any load. It became possible.

〔The invention's effect〕

With the above configuration, the positive acceleration of the variable speed induction motor can be controlled and the negative (braking) acceleration can be controlled by comparing the rotation speed of the motor or the acceleration due to the change in the rotation speed with the process in the operation process storage unit. And speed control, eliminating the need for pole number switching, inverters, and mechanical transmissions. For example, in loads such as automatic warehouses, negative accelerations and speeds that do not collapse are stored in the operating process storage unit, and safety is maintained. The operation of an automatic warehouse or the like is realized quickly and inexpensively by rotating the rotating stator.

Therefore, it is possible to diversify the torque and expand the applications of variable speed induction motors that can generate high torque from low speeds to the rated rotation range, and to make a greater contribution to all fields that require high torque motors. Was.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a multiple stator induction motor, FIG. 2 is a diagram showing a configuration of an embodiment, FIG. 3 is a block diagram of the embodiment, FIG. 4 is an operation process diagram of the embodiment, FIG. FIG. 6 is a torque characteristic diagram of the induction motor according to the present invention, FIG. 6 is a connection diagram of the stator winding and the reverse phase device and the Y-Δ switching device, and FIG.
FIG. 8 is a diagram of a braking torque characteristic in parallel Y connection, FIG. 9 is a connection diagram of the second embodiment, and FIG. 10 is a sequence circuit of the second embodiment. Figure, No.
FIG. 11 is a braking torque characteristic diagram of the second embodiment. 1 ... variable speed induction motor, 2,3 ... rotor core, 4 ...
Rotor shaft, 5: non-magnetic core, 6: rotor derivative,
7 ... rotor, 8 ... short-circuit ring, 9 ... resistance material, 10, 11 ...
... stator winding, 12 ... first stator, 13 ... second stator,
14 ... machine frame, 15 ... bearing, 16 ... rotating stator, 17 ... gear, 20 ... rotating electric motor, 21 ... driving gear, 22 ...
Speed detector, 30 ... Power supply, 31 ... Power switchgear, 32 ...
Control unit, 33 ... Operation process storage unit, 34 ... Control device, 35 ...
... stator rotating device, 37 ... calculating means, 38 ... comparing means,
39 ... signal output means, 40 ... signal input means, 41 ... control means, 42 ... external signals, 43 ... reverse phase device, 44 ... Y-Δ
Switching device, 45, 47, 50, 51, 54, 56 ... Coil, 46, 48, 52, 5
3,55 ...... relay, 60 ...... switching _{device, M 1, M 2, M} 3, M 4, M 5, M 6,
M ₇ …… Switch.

Claims (4)

(57) [Claims] The present invention has two rotor cores which are mounted on the same rotating shaft with an arbitrary gap therebetween, and a plurality of conductors communicating with the two rotor cores are provided and integrally formed. A rotor and two stator cores are provided in parallel with each other and opposed to the two rotor cores, and the windings wound on each stator core are connected to each other in parallel with each other by two fixed cores. And a connecting member for short-circuiting the plurality of conductors to each other at an arbitrary gap between the two rotor cores, wherein at least one of the two stators is a rotor. In a variable speed induction motor formed on a rotating stator concentrically rotating, a controller for controlling a rotating driving device for rotating the stator switches the direction of the rotating magnetic field of the stator in the opposite direction. A negative-phase device and a Y-Δ switching device for switching the stator winding by Y-Δ are connected. Continued City, variable speed induction motor during reverse phase braking actuating the reverse-phase system, characterized in that the Y connect Y-delta switching device from the connection delta. 2. The variable speed induction motor according to claim 1, wherein the magnitude of the braking torque is controlled by changing the phase difference by a rotary drive device. 3. A voltage adjusting device according to claim 2, wherein a voltage adjusting device is provided on said stator and connected to a control device, and voltage control is performed by the voltage adjusting device subsequent to rotation control of the rotary drive device. Shift induction motor. 4. A rotor having two rotor cores mounted on the same rotating shaft with an arbitrary gap therebetween, and a plurality of conductors communicating with the two rotor cores are provided and integrally formed. A rotor and two stator cores are provided in parallel with each other and opposed to the two rotor cores, and the windings wound on each stator core are connected to each other in parallel with each other by two fixed cores. And a connecting member for resistively short-circuiting the plurality of conductors at an arbitrary interval between the two rotor cores, wherein at least one of the two stators is a rotor. A variable speed induction motor formed on a rotating stator concentrically rotating with a power supply connected to a power source during operation and a switching device for short-circuiting a winding terminal during braking is provided on one of the stator windings. A reverse phase device, sometimes connected in normal phase and connected in reverse phase during braking, is provided on the other stator winding A variable speed induction motor characterized by the following: