JPS58179195A - Speed controlling method for induction motor - Google Patents

Abstract

PURPOSE:To enhance the speed controlling accuracy by increasing the resistance of the secondary side resistor of an induction motor at the time of stalling or applying steady tension, thereby increasing the torque and preventing the stalling of the motor. CONSTITUTION:Contactors 54 are all shortcircuited in response to the signal of a controller 58 at the normal operation time, and a wound-rotor type induction motor 51 is controlled at the speed in response to the voltage and frequency applied from an inverter 38. When the slip obtained by calculation in the controller 58 exceeds an allowable value or when a steady tension is applied, the contactors 54 are switched by the output of the controller 58, thereby increasing the resistance value of the secondary side external resistor 52.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed control method for an induction motor, and is particularly suitable for use in a drive system for driving a load that is likely to stall or fall, such as a dummy bar hoisting device of a continuous casting machine or a crane. The present invention relates to an improvement in a preferred speed control method for an induction motor in which the speed of the induction motor is variable-speed controlled by an inverter.

Generally, a continuous casting machine has a ladle 12 placed on a swing tower 10 or a long nozzle 1, as shown in FIG.
4t? A tundish 16 that temporarily holds the molten steel injected through the tundish 16, a mold 20 into which the molten steel is injected from the immersion nozzle 18 disposed at the bottom of the tundish 16, and a tundish 16 that is cooled from the surroundings and formed by the mold 20. a spray device 23 for further secondary cooling of the cast slab 22, and a slab drawing device 24 having pinch rolls 25 for bending the slab 22 in the horizontal direction when the mold 20 also pulls it out; A slab cutter 26 for cutting the completely coagulated slab 22 into predetermined dimensions, an unloading table 28 for unloading the slab cut into predetermined dimensions by the slab cutter 26, and the mold. The mold oscillation [1130] applies vertical vibration to the mold 2o to reduce the friction between the solidified slab shell in the mold 20 and the mold copper plate, and prevents seizure. A narrow dummy par 32 closes the area and guides the slab 22 to the pinch roll 25 as the scorching progresses, and a pinch roll 2 where the tip of the slab 22 is the final one.
5, the slab 22 is also separated from the damino<-
32 is wound up to the height of the mold 20 in order to reuse it.A hook 34b is attached to the tip of the ninth wire 34a.
The next dummy bar winding [34] and the cough damino (-
A refined dummy truck 3 is transported to the position of the Tamino ζ-32t mold 20 hoisted up by the hoisting device 34.
6, a termi bar 32t carried by the dummy car 36, and a chain conveyor (not shown) for inserting into the mold 20 from above.

In such a continuous casting machine, the 9m steel filled in the nodal 12 placed on the swing tower 10 is once passed through the foot opening/gun nozzle 14 formed at the lower part of the ladle 12 and is then turned into a metal/date. / Injected into Yu16. Then,
Injection is carried out into the mold 20 through an immersion nozzle 18' (Il-) formed at the bottom of the tongue pusher 16.The bottom of the mold 20 is filled with a dummy/
It is closed by 32 to prevent the molten steel from falling in the mold at the start of pouring. Further, the molten steel in the mold is given vertical vibration by the mold oscillation device 30 to prevent it from sticking to the mold. Primary 1↓ with mold 20,
The slab 22 is then cooled by the spray device 23.
Pinch roll 25 and pull out 1. The pinch roll 25 is placed on the tip of the slab 22 (which is completely solidified, and the dummy bar 32 is placed at the tip of the slab 22).
Next, the slab is cut to a predetermined size by a slab cutter 26 and carried out by a carry-out table 2B.Meanwhile, the slab is separated from the tip of the slab 22 by the ratio side of the pinch rolls 25. The dummy bar 32 is hooked by the hook 34b of the dummy hoisting device 34, and the dummy bar 32
The continuous casting machine is hoisted up to position 36, then carried to the mold 20 by an arrow, and then inserted into the mold 20 at the start of the next casting to be used again. The above-mentioned termiper winding @34f, which is also useful in
(2) It is possible to perform synchronized operation with the pinch roll 25 and torque control with high precision, (3) dummy / ( - 3
If 2 stalls and falls, it will cause a serious accident, so functions such as being able to reliably prevent stalling are required. Therefore, conventionally, a thyristor Leonard control system for a DC motor has been used in which a DC motor is used as the motor and the speed is controlled by changing the terminal voltage of the DC motor. The thyristor Leonard control system of this DC machine is a highly reliable (and high-performance drive system), but it is a friend of the DC machine.
Since there are brushes and commutators, there was a problem in that it required a lot of maintenance work such as periodic inspection, brush replacement, and repair.

In order to solve these problems, it is conceivable to change the electric motor to a squirrel cage induction motor and adopt an inverter control system. 389 inverter devices used in this inverter control system, as shown in FIG. 2, the commercial AC voltage total DC voltage VDCK supplied from the commercial power supply 40
A converter 42 for converting, a smoothing axle 44 for smoothing the DC voltage VDC output from the converter 42, and an inverter 46 for converting the DC voltage smoothed by the smoothing reactor 44 into an AC voltage VAC having an arbitrary frequency if. and a control circuit 487 that gives a voltage command to the converter 42 and a frequency command to the inverter 46 in accordance with a speed command given from the outside, and controls the commercial AC voltage supplied to the converter 42. is converted into a DC voltage vDc, smoothed by a smoothing reactor 44, converted into an AC voltage VACKf of an arbitrary frequency f by an inverter 46, and then applied to a squirrel cage rust conduction motor 50. The rotational speed N(
rprn) is calculated using the following formula %, where the number of poles of the squirrel-cage type rust-conducting electric rock 50 is P5 power frequency (if (Hz)), and the slip is S.
Formula % (1) Therefore, by changing the power supply frequency f, the speed can be varied. However, Dingbeli S=0.02~0
,05. The generated torque Tm (N-rn) of such a squirrel-cage conductive motor is the internal S-induced electromotive force Eo (V
), excitation inductance is LM (H), secondary current is Iy
(A), it becomes as shown in the following formula.

E.

Tm=ni□・■o・・・・・・・・・・・・・・・・
(2) 2πfLM Here, K is a proportionality constant.

Therefore, in an inverter control system for such a squirrel cage induction motor, in general, in order to obtain a constant torque characteristic in which the generated torque Tm is proportional to the secondary current,
Voltage VAC/frequency f constant control is performed. here,
Since the applied AC voltage vAc is proportional to the DC voltage VDC,
In the end, VDc/f becomes constant.

Using such an inverter control system, it is possible to control the speed of the squirrel cage induction motor 50, but conventionally, if the speed is locked at zero for some reason, it is possible to control the speed of the squirrel cage induction motor 50. ,@,? The drive system tC cannot reliably prevent the phenomenon in which the electric motor stalls due to insufficient torque, reverses rotation, or falls due to insufficient torque.
It could not be used against. In other words, the slip-torque characteristic of the squirrel-cage fat conduction motor has a downward-sloping torque characteristic to the left as shown in Fig. 13, and when the full voltage is at the rated frequency, the current and torque are as shown in Fig. 3 by the solid lines ■, respectively. On the other hand, when the inverter applies a current limit, the torque is proportional to the square of the current, so the current and torque are shown by the broken lines I, , As shown by T, the torque T becomes extremely small where the slip S is large. Therefore, for some reason, the load side torque becomes T. If the speed exceeds , the S will move further to the left and the vehicle will stall and come to a stop.

In addition, if the static tension is too high, the load torque and motor torque are balanced at point a in Figure 4, and the motor is stationary (suberi S-1).
(, -C exists. However, if the load torque suddenly increases for some reason and the load side suddenly reverses, the torque characteristic will drop to the left, so the slip S will shift to the left and the motor will be reversed by VC1ゎ. It stalled.

On the other hand, it is also conceivable to use a wound type induction motor provided with a secondary side resistance as the induction motor, and to control the speed of the wound type induction motor by changing the secondary side resistance. In secondary resistance control of this wound induction motor, the secondary resistance is increased (and the torque curve is shown in Figure 5).
r+, r mushroom, rl, r4 (varies, for example, if the load side torque is TL, slipping is Slb 8
8% 84, and the speed changes. According to this secondary resistance control, the torque increases to the left, so there is no need to worry about stalling as described above, but it has the disadvantage that not only is the speed control accuracy poor, but the shift range is narrow at about 1:3. Was.

The present invention has been made to eliminate the above-mentioned conventional drawbacks, and an object thereof is to provide a speed control method for an induction motor that can prevent stalls in inverter control, has high speed control accuracy, and has a wide speed change range. shall be.

In the present invention, when an induction motor is variable speed controlled by an inverter, a wound type induction motor equipped with a secondary side resistance is used as the induction motor, and during normal operation, voltage/frequency control is performed by the inverter. When stalling or applying stationary tension, increase the resistance value of the secondary resistance,
The above object is achieved by increasing torque when slippage is large and preventing stall.

The present invention will be explained in detail below.

As shown in FIG. 6, the drive system for carrying out the present invention includes a rotor 51m, a slip ring, and a brush 51b.
, the wound induction motor 51 to which the secondary external resistance 52 is connected, the contactor 54 for increasing or decreasing the secondary external resistance 52 of the wound induction motor 51, and the wound induction motor 51. for variable speed control of the wound induction electric model 51' by controlling the applied voltage/frequency;
Front W, an inverter device 38 as shown in FIG.
During normal operation, a voltage/frequency command is output to the inverter device 38 according to the deviation between the output speed signal and a speed command set externally, and the calculated slip S
When stalling exceeds the allowable WL, or when static tension is applied,
The control device 58 increases the resistance of the secondary external resistance 52 by switching the contactor 54, thereby increasing the torque and preventing stall.

The speed control method according to the present invention will be explained in detail below.

A speed command is manually inputted to the control device 58 from the outside, and a voltage/frequency command is sent from the control unit 11t58 to the inverter device 38 according to the deviation between this speed command and the speed signal of the output of the tacho generator 56. Output. During normal operation, the contactors 54 are all short-circuited in response to a signal from the control device 58, so that the winding induction motor +fi
The speed of the motor 51 is controlled according to the voltage and frequency supplied from the inverter device 38, for example, by constant voltage/frequency control.

On the other hand, if the slip S determined by calculation in the control device 58 is the allowable value 'f: 1e9, it is determined that the stall has occurred, and by switching the contactor 54, the resistance value of the secondary external resistance 52 is determined. increase. As a result, the torque curve of the wound induction motor 51 changes from the state shown by solid line A to the state shown by solid line B in FIG. Therefore, the load curve T
If L is, for example, as shown by the broken line in FIG. 7, the operating point will be S9 point from the left, and stall will be prevented.

Further, when the load decreases, the contactor 54 is switched to gold to short-circuit the resistance value of the secondary external resistor 52 and return to the original state.

Furthermore, when static tension is applied, the contactor 54 is switched in advance according to the output of the control device 58, and the secondary external resistance 52 is
By increasing the resistance value of (. Then, the wound induction motor 5
The torque curve of No. 1 changes from the state shown by the solid line C in FIG. 8 to the state shown by the solid line, and since the torque curve becomes one on the upper left, there is no fear of stalling. On the other hand, if the resistance value is not changed and the torque curve is changed to the solid line C in Fig.
Since the state shown in is still the same and the torque curve is on the lower left, there is a possibility of stalling.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a dummy par hoisting device in which the speed control method for an induction motor according to the present invention is adopted will be described in detail with reference to the drawings.

In this embodiment, a swing tower 1 as shown in FIG.
0. In a continuous casting machine having a tundish 16, a mold 20, a spray device 23, a slab drawing device 24, a slab cutter 26, a take-out table 28, a mold oscillation device 30, and a dummy bar hoisting device 34, the dummy bar hoisting device 34 is As the electric motor, an fF-@@ type groove conduction motor 51 equipped with a secondary external resistance 52 as shown in FIG. 6 above is used, and the wound induction motor 51
(During normal operation, the voltage/frequency is kept constant by the inverter device f138. On the other hand, when stalling or static tension is applied, the resistance value of the secondary external resistor 52 is increased to increase the torque when the slip is large, thereby performing control to prevent stalling. It is something.

For example, the wound induction motor 51 has a rating of 7.
A 5Kv190V 4-pole winding induction motor is used, and the inverter device 38 has a rating of 30Kv 230V.
A vector controlled pulse width modulation controlled transistor inverter with a frequency range of 2 to 50 Hz can be used.

FIG. 9 shows an example of changes in speed and torque of the stop cloth after deceleration, from pinch roll synchronized operation to high-speed hoisting and deceleration during steady operation in this example. Fig. 10 shows an example of how the speed and torque change over a wide range of speeds.As is clear from Figs. , stalling is also reliably prevented.

In the above embodiment, the present invention is applied to a drive system for a dummy bar hoisting device of a continuous casting machine, but the scope of application of the present invention is not limited to this, and a speed change range of about 1:30 is required. It is clear that it can be similarly applied to the speed control of dummy bar chain conveyors and table rollers, or to drive systems that drive loads that are at risk of stalling and falling, such as general cranes and hoisting machines. .

As explained above, according to the present invention, it is possible to prevent stalling in inverter control of an induction motor, and to perform variable speed control of an induction motor with high speed control accuracy and over a wide speed change range. It has an excellent flame effect.

[Brief explanation of the drawing]

Figure 1 is a front view showing the general configuration of a continuous casting machine, Figure 2 is a circuit diagram showing the configuration of an inverter device used for speed control of a conventional squirrel cage induction motor, and Figure 3 is a front view showing the general configuration of a continuous casting machine. ,
Similarly, FIG. 4 is a diagram showing an example of the torque-torque characteristics of a squirrel cage induction motor to explain the conventional drawbacks.
FIG. 5 is a diagram showing the slip position on the torque curve when static tension is applied. FIG. 5 is a diagram showing the changing state of the torque curve in secondary resistance control of a conventional wound induction motor. FIG. FIG. 7 is a block diagram including a partial circuit diagram showing the configuration of a drive system for a wound type induction motor in which the speed control method for an induction motor according to the present invention is adopted. 8 is a diagram showing the state of change in the torque curve when static tension is applied, and FIG. 9 is a diagram showing the state of change in the torque curve when static tension is applied. ) A diagram showing an example of changes in speed and torque during steady operation in an embodiment of a dummy bar hoisting device of a continuous casting machine in which the method is adopted, FIG.
FIG. 3 is a diagram showing an example of changes in speed and torque during a dummy parlock test. 16... Tanditshu, 20... Mold, 22
... Slab, 23... Spray device, 24... Slab drawing device ff, 30... Mold oscillation device, 32... Dummy bar, 34... Dummy bar hoisting device, 38... - Inverter device, 42... converter, 44 - smoothing reactor, 46... inverter, 51
...Wound decoration conduction motor, 52...Secondary side external resistance,
54... Contactor, 56... Tacho generator, 58
...Ill tail i Ill. Figure 1,,,1 -Sub'υ5 Figure 5 Figure 6 to Figure 7 NS Figure 8 Figure 9-B% t'a'1 Figure 10

Claims (1)

[Claims] (1) Induction motor When variable speed control is performed by all inverters, a wound type induction motor with a secondary side resistance is used as the induction motor, and during normal operation, voltage/frequency control is performed by the inverter, while stalling 5. A speed control method for an induction motor, characterized in that when a static tension is applied, the secondary side resistance value is increased to increase torque when slip is large and prevent stalling.