JP2013013242A - Apparatus for controlling induction motor and method for controlling induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To implement higher torque control than usual without compromising device durability in controlling an induction motor.SOLUTION: An apparatus for controlling an induction motor includes: a torque characteristic setting device 21 for determining a time series value of required torque depending on operating conditions of an induction motor, comparing the required torque with a torque control pattern of predetermined torque depending on the rotational speed of the induction motor to check whether or not it is satisfied, and if the required torque is not satisfied in a speed range up to a BASE speed, modifying the torque control pattern to increase a maximum value of exciting current under constant torque control, or if the required torque is not satisfied in a speed range higher than the BASE speed, modifying the BASE speed to a higher position than usual; and magnetic flux command modification devices 140 for modifying a magnetic field control pattern in accordance with the modified torque control pattern.

Description

  The present invention relates to an induction motor control device and an induction motor control method, and more particularly to control for temporarily obtaining torque higher than usual.

  In a rolling mill, a material to be rolled is rolled using an induction motor. In a general induction motor, control is performed with a constant torque up to a base speed, and control is performed from a base speed to a top speed in such a way that the motor output is constant (constant power).

  In a rolling mill, with the tension applied to the material to be rolled on the entry side and the exit side of the rolling mill, the material to be rolled is crushed and processed between rotating work rolls, and the processed material to be rolled is extruded. The rolling process is executed continuously. And in a rolling mill, an electric motor is used in order to give a to-be-rolled material tension | tensile_strength and to obtain the rotational force required for a process.

  An electric motor having a torque-speed characteristic capable of obtaining a torque or output necessary for rolling operation is selected and installed at the time of facility planning. As a method of changing the torque-speed characteristics of the induction motor, a method of increasing the torque in the low speed region (for example, refer to Patent Document 1) or the like can be used instead of sacrificing the torque in the high speed region. Instead of narrowing the speed range, there is a method of keeping the torque high (see, for example, Patent Document 2).

  On the other hand, as a specific process for changing the torque-speed characteristics of the induction motor, a method of using as a motor having different characteristics by switching and using a plurality of field patterns stored in advance in motor control. (For example, refer patent document 3) and the method (for example, refer patent document 4) which acquires a big motor torque by correct | amending a field in motor control are proposed.

JP 2006-42562 A JP 2006-42570 A JP 2000-116199 A JP-A-8-70600

  At the time of facility planning, a material to be rolled that becomes a certain product is assumed, and an electric motor capable of obtaining an output that can be produced is selected. In that case, if the electric motor is selected in consideration of the material to be rolled that has a very low production opportunity, the output of the electric motor is wasted in the majority of rolling operations. Moreover, it may occur that it is necessary to roll a material to be rolled that requires a torque or output that exceeds the assumption at the time of facility planning. In such a case, at present, for example, rolling is performed by reducing the rolling reduction and suppressing the torque. Since the plate thickness required for the product is determined by the product specifications, reducing the rolling reduction has led to an increase in the number of rolling operations, resulting in a decrease in operation efficiency.

  In order to solve the above problems, it is necessary to change the torque characteristics of the electric motor so that a high torque can be temporarily obtained in the BASE speed region. Here, the BASE speed is generally a speed corresponding to the highest torque in an available speed range. In addition, in machine tools other than rolling equipment to which induction motors are applied, railway vehicles, transport equipment, and the like, torque required for the electric motor may fluctuate greatly depending on operating conditions. If the required torque is greater than the motor output torque, the operating condition cannot be satisfied. Even in such a case, if the torque characteristics of the electric motor can be changed so as to obtain a high torque, it can be dealt with.

  In this case, as described in Patent Document 3, when a plurality of pre-stored field patterns are selected and used, the motor can be used only with a predetermined field pattern, and the motor performance cannot be sufficiently exhibited. . Further, as disclosed in Patent Document 4, when a large torque can be obtained by correcting the field, when the rotational speed increases, the terminal voltage of the motor increases, and when the maximum voltage is reached, the field is reduced. There is a problem that the output torque decreases because it needs to be weakened.

  As described above, in the control of the induction motor for temporarily obtaining a high torque, it is necessary to set at least one of the torque current and the excitation current to a value higher than that in the normal control. This can be realized by increasing the voltage applied to the induction motor. However, there is a limit to the voltage allowed in the induction motor, and application of a voltage exceeding the limit causes failure of the apparatus and deterioration of durability.

  An object of the present invention is to enable control at a higher torque than usual without impairing the durability of the apparatus in controlling an induction motor.

  One aspect of the present invention is a control device for an induction motor, in which a torque value required according to the operating condition of the induction motor is obtained in a time series, and the torque according to the rotation speed of the induction motor is determined in advance. When the required torque value is satisfied by comparing with the torque control pattern, the required torque value is not satisfied in the speed range slower than the predetermined rotation speed. The torque characteristic setting device 21 that changes the torque control pattern so that the maximum value of the excitation current in the constant torque control becomes high, and the magnetic flux command change device 140 that changes the magnetic field control pattern according to the changed torque control pattern. It is characterized by including.

  According to another aspect of the present invention, there is provided a method for controlling an induction motor, wherein a torque value required according to an operating condition of the induction motor is obtained in a time series, and the torque according to the rotation speed of the induction motor is obtained. By comparing with a predetermined torque control pattern, it is confirmed whether or not the required torque value is satisfied, and the required torque value is satisfied in a speed region slower than the predetermined rotational speed. If not, the torque control pattern is changed so that the maximum value of the excitation current in the constant torque control is increased, and the magnetic field control pattern is changed according to the changed torque control pattern.

  By using the present invention, the induction motor can be controlled with a torque higher than usual without impairing the durability of the apparatus.

It is a figure showing the whole rolling device composition concerning an embodiment of the present invention. It is a figure which shows the structure of the electric motor control apparatus which concerns on embodiment of this invention. It is a figure which shows the structure of the electric motor control apparatus which concerns on embodiment of this invention. It is a figure which shows the equivalent circuit of the induction motor which concerns on embodiment of this invention. It is a figure which shows the vector relationship of the electric current and voltage of the induction motor which concern on embodiment of this invention. It is a figure which shows the torque-speed characteristic in control of a general induction motor. It is a figure which shows the type | formula of the electric torque required for rolling. It is a figure which shows the example of the torque-speed characteristic calculated | required by the induction motor. It is a figure which shows the torque-speed characteristic of the induction motor which concerns on embodiment of this invention. It is a figure which shows the torque-speed characteristic of the induction motor which concerns on a prior art. It is a figure which shows the relationship between a torque magnification and the change of a line current. It is a figure which shows the torque-speed characteristic of the induction motor which concerns on embodiment of this invention. It is a figure which shows the torque-speed characteristic of the induction motor which concerns on embodiment of this invention. It is a figure which shows the control system structure of the induction motor which concerns on embodiment of this invention. It is a figure which shows the rolling operation state which concerns on embodiment of this invention. It is a figure which shows the comparative example of the torque-speed characteristic which concerns on embodiment of this invention, and required torque. It is a figure which shows the comparative example of the torque-speed characteristic which concerns on embodiment of this invention, and required torque. It is a figure which shows the change operation | movement of the torque-speed characteristic which concerns on embodiment of this invention. It is a figure which shows the change operation | movement of the torque-speed characteristic which concerns on embodiment of this invention. It is a figure which shows the change aspect of the torque electric current command which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, a case where the present invention is applied to a single stand rolling mill will be described as an example. FIG. 1 shows the configuration of a single stand rolling mill. The single stand rolling mill has an entry side TR (a tension reel is abbreviated as TR) 2 on the entry side with respect to the rolling direction of the rolling mill 1 and an exit side TR3 on the exit side. This is done by rolling the rolled material with the rolling mill 1 and then winding it with the exit side TR3.

  The rolling mill 1 includes a roll gap control device 7 for controlling the plate thickness of the material to be rolled by changing the roll gap, and a mill speed control device 4 for controlling the speed of the rolling mill 1. Is installed. The entry-side TR2 and the exit-side TR3 are driven by an electric motor, and an input-side TR control device 5 and an output-side TR control device 6 are installed as devices for driving the electric motor and the electric motor. Commands to these control devices are output from the rolling control device 20.

  In the single-stand rolling mill, reverse rolling is performed to change the rolling direction, so that the entry side and the exit side are reversed depending on the rolling direction. Is the entrance tension reel, and the right side of the rolling mill is the exit tension reel.

  During rolling, a speed command is output from the rolling speed setting device 10 to the mill speed control device 4, and the mill speed control device 4 performs control to keep the speed of the rolling mill 1 constant. On the entry side and the exit side of the rolling mill 1, rolling is performed stably and efficiently by applying tension to the material to be rolled. It is the entry side tension setting device 11 and the exit side tension setting device 12 that calculate the necessary tension.

  The entry-side tension current converter 15 and the exit-side tension current converter 16 calculate the set tension based on the entry-side and exit-side tension setting values calculated by the entry-side tension setting device 11 and the exit-side tension setting device 12, respectively. A current value for obtaining a motor torque necessary for adding to the material to be rolled is obtained. The inlet side tension current converter 15 and the outlet side tension current converter 16 give the respective current values obtained as described above to the inlet side TR controller 5 and the outlet side TR controller 6.

  The entry side TR control device 5 and the exit side TR control device 6 control the motor current so as to be the current given from the entry side tension current conversion device 15 and the exit side tension current conversion device 16. Thereby, a predetermined tension is applied to the material to be rolled by the motor torque applied from the motor current to the entry side TR2 and the exit side TR3.

  The tension current converters 15 and 16 calculate a current set value (motor torque current set value) that becomes a tension set value based on the models of the TR mechanical system and the TR motor control device. Including. Therefore, the entry side tension control 13 and the exit side tension control 14 are set using the actual tension measured by the entry side tension meter 8 and the exit side tension meter 9 installed on the entry side and the exit side of the rolling mill 1. The value is corrected and input to the tension current converters 15 and 16. As a result, the current values set in the incoming TR control device 5 and the outgoing TR control device 6 are corrected. The TR control device referred to here is composed of an electric motor for driving the TR mechanical system and its control device.

  Further, since the plate thickness of the material to be rolled is important for product quality, plate thickness control is performed. The sheet thickness on the exit side of the rolling mill 1 is determined by operating the roll gap of the rolling mill 1 using the roll gap control apparatus 7 by the exit side thickness control apparatus 18 based on the actual sheet thickness detected by the exit thickness gauge 17. Be controlled.

  As described above, in a single stand rolling mill, the TR used for winding and unwinding uses constant torque control that makes the torque generated by the electric motor constant, and uses the actual tension detected by a tensiometer. Control which makes tension applied to a material to be rolled constant by correcting an electric motor current command is performed. Since the motor torque that is actually output is determined from the field and torque current applied to the motor, the current command needs to be changed according to the field in order to make the torque constant.

Rolling is performed by unwinding the material to be rolled from the entry side tension reel 2, rolling the material by the rolling mill 1, and winding the material to be rolled that has been rolled by the exit side tension reel 3. FIG. 2 shows a speed control configuration of the induction motor that is the mill speed control device 4. The induction motor 101 is driven following the speed command N _ref (motor rotation speed command) from the rolling speed setting device 10. The speed command N _ref is a target value for the rotational speed N (r / min). The induction motor 101 is used in production equipment such as hot rolling equipment, cold rolling equipment, and processing line equipment.

The speed controller 104 _generates a torque current command I _qref based on the difference between the speed command N _ref described above and the rotational speed N of the induction motor 101 detected by the speed sensor 103 (N _ref −N). Output to the current controller 107. That is, the speed controller 104 functions as a torque current control unit. Further, the magnetic flux command unit 105 outputs a magnetic flux command φ _ref for the field magnetic flux to the excitation current calculator 106 based on the rotational speed N detected by the speed sensor 103. The magnetic flux command unit 105 is preset with a magnetic flux command φ _ref for the rotational speed N. This magnetic flux command φ _ref for the rotational speed N is used as a magnetic field control pattern.

The magnetic flux commander 105 determines the magnetic flux φ corresponding to the rotational speed N based on the magnetic flux φ-speed characteristic corresponding to the torque-speed characteristic described later. This magnetic flux φ-speed characteristic is the magnetic field control pattern described above. Further, the speed controller 104 outputs I _qref according to (N _ref −N) described above based on a torque-current conversion coefficient according to torque-speed characteristics described later. This torque-speed characteristic is stored in the magnetic flux command change device 140. When the torque-speed characteristic is changed, the magnetic flux command change device 140 changes the speed controller 104 and the magnetic flux command device 105 after the change. Torque-current conversion coefficient and magnetic flux φ-speed characteristics corresponding to the torque-speed characteristics are respectively set.

The exciting current calculator 106 calculates the exciting current of the induction motor 101 based on the magnetic flux command φ _ref from the magnetic flux commander 105 and outputs the exciting current command I _dref to the exciting current controller 106. That is, the magnetic flux command unit 105 and the excitation current calculator 106 function as an excitation current control unit. The current calculator 109 calculates the torque current I _q and the excitation current I _d based on the primary current (stator current) flowing through the induction motor 101 detected by the current sensor 110. That is, the current calculator 109 converts the line current of the induction motor 101 into a q-axis and d-axis coordinate system that rotates in synchronization with the power frequency of the output of the power converter 112. Then, the current calculator 109 outputs the torque current _{I q} and the exciting current _{I d} computed.

The torque current excitation current controller 107 includes a torque voltage command V _q for causing the torque current I _q output from the current calculator 109 to follow the torque current command I _qref output from the speed controller 104, and a current calculator. An excitation voltage command V _d for causing the excitation current I _d output from 109 to follow the excitation current command I _dref output from the excitation current calculator 106 is output to the coordinate converter 111. Since the setting of the frequency of the output of the current calculator 109 is a well-known technique, the description regarding it is omitted in FIGS.

The coordinate converter 111 converts the torque voltage command V _q and the excitation voltage command V _d described above into a fixed coordinate system, and generates a voltage command V for three phases. Then, the coordinate converter 111 outputs the generated voltage command V to the power converter 112. The power converter 112 is a PWM (pulse width modulation) inverter, for example.

  The power converter 112 converts the power of the DC power supply 113 (for example, PWM conversion) based on the voltage command V, and supplies three-phase AC power to the induction motor 101. With this configuration, the primary current of the induction motor 101 is controlled, and the speed control of the induction motor 101 is performed.

In the entrance side TR control device 5 and the exit side TR control device 6, current control is performed to keep the tension applied from the TR to the material to be rolled constant. FIG. 3 shows a current control configuration of the induction motor. Unlike the case of speed control, in the case of current control, since I _ref that is the torque current command I _qref is directly given, it is the same as the speed control configuration of FIG. 2 except that the speed controller 104 is not provided.

FIG. 4 shows a T-type equivalent circuit for one phase of the induction motor. Excitation current I _d flows in the excitation circuit, the torque current I _q has to flow in the stator circuit. Exciting circuit is configured to include a excitation circuit inductance L _m, the stator circuit is configured to include a resistance obtained by subtracting the S sliding rotor circuit resistance R2 (R2 / S). The excitation current I _d and torque current I _q primary current obtained by the square root of sum of squares of (stator current) I _s is made to flow in the stator winding.

Incidentally, shown in FIG. 4, _{V s} is the terminal voltage, R1 is the stator circuit resistances, L1 stator circuit inductance, L2 is the rotor circuit inductance, _{E d} is the internal induced electromotive force (excitation circuit voltage). The relationship between the current and voltage of the T-type equivalent circuit shown in FIG. 4 is shown by the vector diagram in FIG. From this vector diagram, the relationship between the terminal voltage V _s and the internal induced electromotive force E _d is determined. ω represents a power supply angular frequency.

ここでＫ_１´、Ｋ_２は誘導電動機の特性によって決まる係数である。 Here, the field φ and the torque T _q of the induction motor 101 can be calculated by the following equations (1) and (2).

Here, K ₁ ′ and K ₂ are coefficients determined by the characteristics of the induction motor.

If the electric constant of the induction motor is known, the excitation current I _d can be obtained from the above equation (1), and if the torque required for rolling is further found, the torque current I _q can be obtained from the equation (2). Further, the line voltage V _s for obtaining them can be obtained from the following equations (3) to (4) from FIG.

Next, control characteristics of the induction motor will be described. FIG. 6 is a diagram illustrating general control characteristics of the induction motor. The induction motor is controlled by constant torque control that keeps the output torque constant up to a BASE speed that is a predetermined rotation speed that is set in advance, and a constant output that keeps the motor output (power) constant from the BASE speed to the TOP speed. Controlled by control. Therefore, if the torque current is constant, the output torque is constant until the BASE speed, and the torque decreases in inverse proportion to the rotational speed above the BASE speed. Further, the internal induced electromotive force _Ed is maximized until the BASE speed is reached, and the value is maintained during the constant output control.

The magnetic flux command unit 105 is configured so that the internal induction electromotive force E _d is proportional to the increase in the rotational speed N (angular speed ω) of the induction motor 101 according to the equation (1) so that the field is constant during constant torque control. To increase. When the angular velocity ω reaches BASE speed, keeping the internal induced electromotive force E _d constant. Thus, above the BASE speed, the field φ decreases in inverse proportion to the angular velocity ω, and the output torque T _q also decreases in inverse proportion to the speed. At this time, from the equations (3) to (5), the line voltage V _s increases as the angular velocity ω increases. The angular speed ω at which the line voltage V _s reaches the line maximum voltage V _sMAX becomes the TOP speed, and the induction motor cannot rotate at a higher speed.

  In the rolling mill, the motor of the mill and TR has a speed-torque characteristic as shown in FIG. 6 determined from the maximum speed at which the rolling operation is performed, the required maximum torque, and the like according to the purpose of the rolling equipment. Electric motors with characteristics are manufactured and installed.

FIG. 7 shows an example of a formula for the motor torque required for rolling. From the product specification and the rolling mill specification, the torques T _qETR , T _qMILL , T _qDTR required for the _entry side TR2, the rolling mill 1, and the _delivery side TR3 are _calculated . Can be sought. An electric motor in which this torque can be obtained at the motor rotational angular speed ω determined from the rolling speed required for operation is required for the rolling equipment. The electric motor rotation angular velocity ω can be obtained from the rolling speed using the rolling mill specifications. The rolling speed can be determined in consideration of operation efficiency, product specifications of the material to be rolled, and the like.

  FIGS. 8A to 8C show a simple example of torque-speed characteristics necessary for rolling. In FIGS. 8A to 8C, required torque and speed combinations are indicated by asterisks. In the case of FIG. 8A, the torque-speed characteristic required for rolling can be satisfied by selecting an electric motor having the torque-speed characteristic A.

  On the other hand, in the case of FIG. 8B, the torque-speed characteristic A is not satisfied in the low-speed region. Therefore, in order to satisfy the torque-speed characteristic in the entire speed range, an electric motor having the torque-speed characteristic B is required. This requires a motor with a large output, increases the capacity of the motor and the motor control device, and increases the amount of capital investment.

  Here, in the example of FIG. 8B, a large torque is obtained in the low speed region. Therefore, if a torque-speed characteristic such that a large torque is generated at a low speed can be obtained with the same motor, the request of FIG. 8 (a) is changed to the request of FIG. 8 (b) using the same motor and motor control device. Can also be satisfied. On the other hand, the terminal voltage that can be applied to the motor has a limit, and the maximum output of the motor has a limit. Therefore, in order to obtain a higher torque than usual, it is necessary to reduce the BASE speed. In other words, when the motor is normally used as a motor having a torque-speed characteristic A and rolling requiring a large torque is performed, the motor controller controls the motor having a torque-speed characteristic C shown in FIG. Then, the required rolling operation can be performed without increasing the capital investment.

To achieve this, the motor speed controller 100 according to this embodiment, to increase the field φ by increasing the E _d in equation (1). In order to realize this, as shown in FIG. 9, the increase rate with respect to the speed change of the terminal voltage V _s is increased so that the maximum terminal voltage V _sMAX is _reached at a low speed. As the maximum terminal voltage V _Smax during the constant power control is maintained, the internal induced electromotive force E _d is the voltage of the induction motor internal excitation circuit is controlled to be lower with increasing rotational speed The

The power of the terminal voltage V _s which is more applied than usual by the increase rate is increased is used to be higher than normal controlling the excitation current I _d. As a result, the magnetic field flux φ is increased, the torque T _q increases. In this case, as shown in FIG. 9, in a predetermined speed region exceeding the BASE speed, the torque obtained is lower than that in the normal control, but the purpose is to obtain a high torque at a low speed. What is necessary is just to restrict | limit a rolling speed.

Another method for changing the torque-speed characteristic is to increase the torque current command. FIG. 10 shows the torque-speed characteristics in that case. In this case, the torque increases in proportion to the increase in torque current. And rise of the primary current I _s in FIG. 9, is compared with the rise of the primary current I _s in FIG. 10, rise of the torque T _q despite the larger 9, 9 If, namely, more aspect to which this embodiment is applied is seen to have less rise of the primary current I _s.

Generally, the exciting current is about 30% of the torque current. For example, when it is desired to increase the torque by 10%, as will be understood from the above formulas (1) and (2), the excitation current is increased by 10% (in the case of FIG. 9) and the torque current is increased by 10% (FIG. 10). If) there is a way. Since the excitation current is about 30% of the torque current as described above, the increase in the line current is smaller when the excitation current is increased by 10%. Incidentally, the line current _{I s} is calculated by the following equation (6).

  FIG. 11 shows the relationship between torque and line current. In FIG. 11, the solid line is a graph showing a change in line current according to the torque magnification when the torque current is changed, and the broken line is a graph showing a change in line current according to the torque magnification when the excitation current is changed. is there. As shown in FIG. 11, the change in the line current is smaller when the torque is changed by changing the excitation current than when the torque current is changed. Therefore, when the torque is reduced, the torque current is operated, and when the torque is increased, the excitation current is operated, so that the induction motor torque can be increased while suppressing the increase of the line current. By suppressing the increase of the line current, heat loss can be suppressed and heat generation of the motor and the motor control device can be prevented.

  FIG. 8D shows a case where there is rolling that requires a torque larger than the torque-speed characteristic A at a speed exceeding the BASE speed. In order to realize this, the torque-speed characteristic D may be used. When the torque-speed characteristic is changed in this way, as shown in FIG. 12, the BASE speed for stopping the increase of the induced voltage according to the speed is increased until the terminal voltage reaches the maximum voltage, and the constant torque rotation is performed. Increase speed range.

  When carrying out rolling that requires a large torque, if rolling is carried out at a low speed, it can be handled by changing the torque-speed characteristics. In this case, as a matter of course, a constraint condition due to the heat generation of the motor, the capacity of the motor control device, and the like occurs, and therefore, it is implemented as much as possible within the constraint condition. In addition, this method can be used even when performing rolling that requires a rolling torque that was not assumed at the time of planning the rolling equipment.

  As described above, the torque-speed characteristics of the electric motor used in the rolling mill are changed by changing the field φ pattern in the electric motor control, so that the applied voltage is allowed within the apparatus. High torque can be obtained efficiently. Therefore, when performing rolling that requires high torque, it is possible to efficiently roll without giving control to impair the durability of the equipment in the current rolling equipment by giving the optimal torque-speed characteristics. It becomes.

In FIG. 9, the BASE speed, that is, the rotation speed of the induction motor that switches from constant torque control to constant output control is made lower than the default value, that is, the rated value, and the constant torque until the BASE speed is reached. The constant voltage control speed at which the terminal voltage V _s reaches the maximum value V _sMAX during the control, the electric power supplied more than the default state is distributed to the excitation current, and field weakening control is performed. In the range, the case where the excitation current _Id is decreased by controlling the internal induced electromotive force _Ed to gradually decrease has been described as an example.

However, the gist of the present embodiment is that the terminal voltage V _s reaches V _sMAX during the constant torque control until the BASE speed is reached, and the power supplied more than the default state is distributed to the excitation current, the torque T _q exerted in the result BASE rate is to be higher than the default state. Therefore, as shown in FIG. 9, it is not always necessary to set the BASE speed to the default state, that is, lower than the rated value, and as shown in FIG. However, the effects according to the present embodiment can be obtained.

Here, when compared with FIG. 10 to FIG. 13, 13, 10 together BASE rate does not change, but the amount of increase in torque is also the same, different increment of the primary current I _s, the case of FIG. 10 better in the case of FIG. 13 it can be seen that increasing the width of the primary current I _s is narrower than the. As described above, by using the induction motor control device and control method according to the present embodiment, even when the same motor output torque is obtained, it is possible to achieve a larger excitation with less line current.

On the other hand, if the desired torque _Tq cannot be obtained with the increase in power obtained by performing the above-described control while maintaining the BASE speed, the value of the BASE speed is set as shown in FIG. By lowering, it becomes possible to obtain a desired torque _Tq at a low speed. The BASE speed is the lowest speed in the range of the speed ω at which constant output control is performed, and the highest speed is the TOP speed.

  Next, a specific configuration for performing control to change the torque-speed characteristic of the induction motor as shown in FIGS. 9, 12, and 13 will be described. FIG. 14 is a diagram showing a control system configuration when changing the torque-speed characteristic of the induction motor according to the present embodiment. As shown in FIG. 1, the mill speed control device 4 having a control configuration of a single stand rolling mill specifically includes an induction motor 1-101 for driving a work roll of the rolling mill 1 and a rotation speed of the induction motor. It consists of a speed sensor 1-103 for detecting and an electric motor speed control device 141.

  The ingress TR control device 5 includes an induction motor 2-101 for driving the ingress TR2, a speed sensor 2-103 for detecting the rotation speed of the induction motor, and an electric motor current degree control device 142. The Similarly, the outgoing TR control device 6 includes an induction motor 3-101 for driving the outgoing TR3, a speed sensor 3-103 for detecting the rotation speed of the induction motor, and an electric motor current degree control device 142. Is done.

A current command I _ref is given to the motor current control device 142 of the entry side TR control device 5 from the entry side tension current conversion device 15 in the rolling control device 20, and from the exit side tension current conversion device 16, A current command I _ref is given to the motor current control device 142 of the delivery side TR control device 6, and a speed command N _ref is sent from the rolling speed setting device 10 to the motor speed control device 141 of the mill speed control device 4. Given. The motor speed control device 141 and the motor current control device 142 control the induction motors 1-101, 2-101, and 3-101 so as to be a given speed command and current command, respectively.

  As shown in FIG. 7, the motor torque required for rolling is determined by the tension of the material to be rolled and the reel diameter for the entry side TR2 and the exit side TR3. Moreover, about the rolling mill 1, it determines with the sum of the torque according to the torque required for the process of a to-be-rolled material, the tension | tensile_strength of the rolling mill 1 entrance and exit, and the roll diameter which an electric motor drives.

  As shown in FIG. 7, the torque characteristic setting device 21 obtains a torque necessary for rolling from the product specification and the machine specification, and compares it with the electric motor characteristics to ensure the necessary motor torque during the rolling. The torque characteristic setting device 21 includes a current control torque characteristic setting device 22 that creates a field change command for the motor current control device 142 driven by a current command such as a tension reel, and a motor speed control driven by a rolling mill speed command. And a speed control torque characteristic setting device 23 for creating a field change command for the device 141.

  The current control torque characteristic setting device 22 receives tension commands on the entry side and the exit side of the rolling mill from the entry side tension setting device 11 and the exit side tension setting device 12, and the rolling speed pattern, the reel radius of the entry side TR2 and the exit side TR3. Thus, the torque-speed characteristic of the electric current controlled motor is determined so that the set tension can be maintained during rolling, and the torque-speed characteristic is changed by sending it to the magnetic flux command changing device 140 of the electric motor current control device 142. To do.

FIG. 15 is a diagram illustrating a rolling operation method. Since rolling is carried out by winding the rolled material fed from the entry side TR2 to egress TR3, before the start of rolling, R _ETR is large, at the end of rolling is R _DTR increases. Also, the rolling speed is gradually increased from 0 at the start of rolling and gradually decreased to 0 by the end of rolling. Since the TR radius changes, the torque required for the motor always changes during the rolling operation.

  The entry side TR requires the largest torque at the start of rolling, and the exit side TR requires the greatest torque at the end of rolling. In rolling, the speed operation is performed based on the speed of the rolling mill. That is, the rolling speed in FIG. 15 is the rolling mill speed. For this reason, when the TR radius is large even when the rolling speed is constant, the motor rotation speed is small, and when the TR radius is small, the motor rotation speed is large. For example, the torque required for the entry side TR is as shown by a solid line in FIG.

  Here, assuming that the torque-speed characteristic of the motor is as indicated by the one-dot chain line in FIG. 16D, the torque of the motor with respect to time is as indicated by the one-dot chain line in FIG. There is a portion smaller than the required torque on the entry side TR (the portion where the motor torque indicated by the broken line ellipse is insufficient). In this part, since the motor torque is insufficient, the tension of the material to be rolled cannot be maintained.

  At this time, if the torque-speed characteristic of the motor is changed as shown in FIG. 16 (e) (when the BASE speed is increased), as shown in FIG. It becomes small and it becomes possible to maintain tension.

  Further, as shown in FIG. 17A, when the motor torque is insufficient in the low speed region, the torque characteristic B shown in FIG. 17D is changed to the torque characteristic C shown in FIG. By reducing the BASE speed and increasing the field current in the constant torque control region until the BASE speed is reached, the tension can be maintained.

  The operation of the current control torque characteristic setting device 22 is shown in FIG. Here, the case where the torque-speed characteristic is changed for the entry TR2 will be described, but the change is similarly made for the exit TR3. As illustrated in FIG. 18, when the current control torque characteristic setting device 22 acquires the tension setting from the entry-side tension setting device 11, the current control torque characteristic setting device 22 responds to the reel radius using the formula described in FIG. 7 based on the acquired tension setting. Necessary torque is calculated (S1801), and as described in FIGS. 16 (a) and 17 (a), a torque value required according to various operating conditions of the induction motor is obtained in time series, and necessary. It is confirmed that the current torque-speed setting is larger than the torque (S1802). That is, in S1801 and S1802, the current control torque characteristic setting device 22 functions as a torque confirmation unit.

  As a result of the confirmation in S1802, if there is no portion below the required torque in the current torque-speed setting (S1802 / NO), the tension can be maintained and the process is terminated as it is. On the other hand, if there is a portion below the required torque in the current torque-speed setting (S1803 / YES), the tension cannot be maintained, and the process of changing the torque-speed setting is started.

  In that case, the processing differs depending on whether or not the reel speed of the portion below the required torque in the current torque-speed setting is equal to or lower than the BASE speed. When the reel speed of the portion below the required torque is equal to or lower than the BASE speed (S1803 / YES), in order to increase the torque, the field current is increased and the BASE speed is increased as shown in FIG. 8 (c) and FIG. Lowering (S1804), a new torque-speed characteristic is created (S1806). That is, in S1806, the current control torque characteristic setting device 22 functions as a torque control pattern changing unit.

  As described above, the field current may be increased while maintaining the BASE speed. For example, when the reel speed of the portion below the required torque is the speed immediately before reaching the BASE speed, the field current is increased while maintaining the BASE speed in order to satisfy the required torque.

  On the other hand, when the reel speed is higher than the BASE speed, the BASE speed is increased by changing the speed timing at which the excitation current starts to weaken to change the torque-speed characteristics as shown in FIGS. Torque-speed characteristics are created (S1806). .

  The new torque-speed characteristic created in S1806 needs to be realizable by the entry-side tension reel motor 2-101 and the motor current control device 142 to be controlled. For this purpose, the line voltage is set to a limit value or less. There must be. Therefore, the current control torque characteristic setting device 22 performs a prediction calculation of the line voltage from the excitation current and the torque current, and if the line voltage exceeds the limit value (S1807 / NO), the change is interrupted. When the rolling is continued, an alarm that cannot maintain the tension is output to the operator (S1808). In that case, the operator selects whether to respond by increasing the torque current or decrease the tension, and continues rolling. Of course, there is an option to stop rolling.

  If the line voltage is within the limit value (S1807 / YES), the current torque-speed characteristic is changed to “torque-speed characteristic change” (S1809), and this is changed to the magnetic flux command changer 140 in the motor current controller. Output. In the magnetic flux command changing device 140, the magnetic flux φ-speed characteristic that gives the given torque-speed characteristic is obtained and set in the magnetic flux command unit 105. That is, the magnetic flux command changing device 140 functions as a magnetic field control pattern changing unit. Here, the magnetic flux-speed characteristic from the torque-speed characteristic can be obtained by a known technique from the electrical characteristic of the induction motor.

  When the torque-speed characteristic of the motor changes, the torque-current conversion coefficient also changes. In the inlet side tension current converter 15, the torque obtained from the inlet side set tension and the inlet reel radius is converted into a current using a torque-current conversion coefficient and output to the motor current controller 142. When the magnetic flux command changing device 140 changes the magnetic flux φ-speed characteristic of the magnetic flux commander 105 by changing the torque-speed characteristic, the torque-current conversion coefficient of the speed controller 104 is also changed accordingly (S1810). That is, the magnetic flux command changing device 140 also functions as a conversion coefficient changing unit that changes the conversion coefficient in accordance with the change of the torque-speed characteristic.

  Here, the case where the torque is calculated from the entry side tension set value set by the entry side tension setting device 11 has been described, but the entry side using the tension detection value in the entry side tension meter 8 as shown in FIG. When the tension control 13 is executed, the input side tension set value + the input side tension control 13 output becomes the input side tension command, and can be dealt with by changing the torque calculation using this. .

  The electric motor 1-101 of the rolling mill 1 is controlled by the electric motor speed control device 141 so that the speed follows the command. Further, in the rolling mill 1, since the material to be rolled is processed by rolling, it is necessary to give the torque required for the material from the electric motor. Therefore, it is difficult to calculate the necessary torque as in the entry side TR and the exit side TR.

As shown in FIG. 7, although it is possible to calculate the torque T _qMILL from the product specification and the machine specification, the rolling mill torque T _qMILL actually required from the calculation error of the torque arm coefficient and the rolling load equation is a calculated value. And often different. Therefore, the speed control torque characteristic setting device 23 calculates the torque required for the motor from the torque current command I _qref which is the output of the speed controller 104 which is actually controlled by the motor speed control device 141, and the result To change the torque-speed characteristics.

  FIG. 19 shows an outline of the operation of the speed control torque characteristic setting device 23. As shown in FIG. 19, the speed control torque characteristic setting device 23 receives a speed controller torque current command, which is an output from the speed controller 104, from the motor speed control device 141, and uses the torque current conversion coefficient to obtain the required torque. An operation is performed (S1901). The subsequent steps are the same as those of the current control torque characteristic setting device shown in FIG. In the case of a rolling mill, as an option when rolling is not possible, it is possible to change the exit side thickness setting of the material to be rolled (change the setting to a thicker) or change the tension (change to a larger setting). Conceivable. The torque-current conversion coefficient changed in S1910 is used in the next process in S1901.

A torque-speed characteristic is given to the magnetic flux command changing device 140 in the motor speed control device 141 to create a magnetic flux-speed characteristic. At the same time, since the magnetic flux is changed, it is also necessary to change the torque current command output from the speed controller 104 in order to keep the output torque of the motor constant. FIG. 20 shows a processing outline. In the speed controller 104, it is _assumed that the torque current command I _qref is obtained by proportional integral control of the speed deviation ΔN. In this case, the torque current command I _qref is the sum of the proportional term I _qPref and the integral term I _qIref as shown in the following formula (7).

Here, in order to change the magnetic flux φ while keeping the motor output torque constant, it is necessary to change the torque current command I _qref according to the change of the field φ. If the field is changed from the field (A) φ _A to the field (B) φ _B before and after the field characteristic switching point, the torque current command in the field (A) is I _qref (A). The torque current command in the magnetism (B) needs to be expressed by the following formula (8).

Here, since the proportional term output I _qPref becomes constant even when the field changes, the proportional term is corrected by the integral term. Therefore, the value of the integral term is changed so as to be the following formula (9). Thereby, even if the field is switched, the motor torque can be made constant before and after the switching.

  In FIG. 20, the case where the field is switched in a step shape has been described, but switching of the field characteristics can be performed in a ramp function in a time of about several seconds. The same applies to the operation of the current control torque characteristic setting device 22.

  As described above, by adopting the configuration as shown in FIG. 14, the torque-speed characteristic of the induction motor can be changed and used during the rolling operation in accordance with the rolling state. Thereby, the range of the material which can be rolled, plate | board thickness, and plate | board width is attained, without changing an electric motor, and it becomes possible to suppress the amount of capital investment. Also, unlike the case where the torque generated by the motor is used to increase the torque generated by the motor, it is possible to suppress an increase in the line current, improving the torque increase rate and reducing the copper loss (current loss due to heat generation). it can. Furthermore, it is possible to avoid impairing the durability of the apparatus by avoiding operation with power exceeding the allowable range.

  In addition, in the said embodiment, as shown in FIG. 1, it demonstrated as an example a single stand rolling mill, but it can be used not only for a single stand rolling mill but also for a tandem rolling mill in which a plurality of rolling mills are continuously arranged. It is.

  Moreover, in the said embodiment, although the induction motor used for a rolling mill was demonstrated as an example, not only a rolling mill but the production machine in which the torque required for the operation | movement requested | required of an electric motor is fluctuate | varied greatly with operating conditions. For example, it can also be used for machine tools, railway vehicles, transport facilities, and the like.

  Further, the rolling control device 20 and the torque characteristic setting device 21 shown in FIG. 14 are realized by a combination of software and hardware. That is, the rolling control device 20 and the torque characteristic setting device 21 include a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a HDD (Hard Disk Drive), and other non-volatile storage media and an LCD ( It has the same hardware configuration as an information processing terminal such as a general server or a PC (Personal Computer) such as a liquid crystal display (LCD), a user interface such as a keyboard and a mouse.

  In such a hardware configuration, a program stored in a recording medium such as a ROM or an HDD is read into the RAM, and the CPU performs an operation according to the program, thereby configuring a software control unit. The functions of the rolling control device 20 and the torque characteristic setting device 21 according to the present embodiment are realized by a combination of the software control unit configured as described above and hardware.

1 Rolling machine 2 Incoming TR
3 Outgoing TR
4 Mill Speed Control Device 5 Incoming TR Control Device 6 Outgoing TR Control Device 7 Roll Gap Control Device 8 Incoming Tension System 9 Outgoing Tension System 10 Rolling Speed Setting Device 11 Incoming Tension Setting Device 12 Outgoing Tension Setting Device 13 Entry-side tension control 14 Entry-side tension control 15 Entry-side tension current conversion device 16 Entry-side tension current conversion device 17 Entry-side plate thickness gauge 18 Entry-side plate thickness control device 20 Rolling control device 21 Torque characteristic setting device 22 Current-torque characteristic setting device 23 Speed control torque characteristic setting device 100 Motor speed control device 101 Induction motor 103 Speed sensor 104 Speed controller 105 Magnetic flux command unit 106 Excitation current calculator 107 Torque current excitation current controller 109 DC current calculator 110 Current sensor 111 Coordinate converter 112 Power converter 113 DC current 115 Speed calculator 120 Motor current controller 140 Magnetic flux command Change device 141 Motor speed control device 142 Motor current control device

Claims (6)

A control device for an induction motor that obtains torque by an excitation current for generating a magnetic field and a torque current for generating a torque corresponding to the magnetic field,
Constant torque control is performed so that the torque remains constant until a predetermined rotation speed is reached, and the excitation current is reduced by decreasing the excitation current from the predetermined rotation speed to the maximum rotation speed. In the constant torque control, the excitation current is fixed at a maximum value, and in the constant output control, the excitation current is increased as the rotation speed is increased. An excitation current control unit for controlling the excitation current according to a magnetic field control pattern for reducing
The required value obtained by obtaining the torque value required according to the operating condition of the induction motor in time series and comparing the torque according to the rotation speed of the induction motor with a predetermined torque control pattern. A torque confirmation unit for confirming whether or not a torque value to be satisfied is satisfied,
The torque control pattern is changed so that the maximum value of the excitation current in the constant torque control is increased when the calculated required torque value is not satisfied in a speed region slower than the predetermined rotational speed. A torque control pattern changing unit to perform,
And a magnetic field control pattern changing unit that changes the magnetic field control pattern according to the changed torque control pattern.   The torque control pattern changing unit is configured to change the predetermined rotation speed to a predetermined rotation in the normal control when the calculated required torque value is not satisfied in a speed region slower than the predetermined rotation speed. 2. The induction motor control device according to claim 1, wherein the torque control pattern is changed so as to be lower than a speed.   The torque control pattern changing unit is configured to change the predetermined rotation speed to a predetermined rotation in the normal control when the calculated required torque value is not satisfied in a speed region faster than the predetermined rotation speed. 3. The induction motor control device according to claim 1, wherein the torque control pattern is changed so as to be higher than a speed. The induction motor is used for rotation of the roll in a rolling mill that rolls by rolling a material to be rolled between at least a pair of rolls,
A torque current control unit for converting the tension command value of the material to be rolled into the command value of the torque current based on a conversion coefficient;
4. The induction motor control device according to claim 1, further comprising a conversion coefficient changing unit that changes the conversion coefficient in accordance with the changed torque control pattern. 5.   When the torque control pattern is changed, the torque control pattern changing unit calculates a value of the line current determined by the excitation current and the torque current supplied to the induction motor after the change, and the calculation result is calculated in advance. 5. An operator is informed whether or not control is impossible when the value of the line current exceeds the limit value by checking whether or not the value is within a predetermined limit value. The control apparatus of the induction motor of any one of Claims 1. A method for controlling an induction motor that obtains torque by an excitation current for generating a magnetic field and a torque current for generating a torque corresponding to the magnetic field,
Constant torque control is performed so that the torque remains constant until a predetermined rotation speed is reached, and the excitation current is reduced by decreasing the excitation current from the predetermined rotation speed to the maximum rotation speed. In the constant torque control, the excitation current is fixed at a maximum value, and in the constant output control, the excitation current is increased as the rotation speed is increased. Controlling the excitation current according to a magnetic field control pattern that reduces
The required value obtained by obtaining the torque value required according to the operating condition of the induction motor in time series and comparing the torque according to the rotation speed of the induction motor with a predetermined torque control pattern. Check whether the torque value is satisfied,
The torque control pattern is changed so that the maximum value of the excitation current in the constant torque control is increased when the calculated required torque value is not satisfied in a speed region slower than the predetermined rotational speed. And
An induction motor control method, wherein the magnetic field control pattern is changed in accordance with the changed torque control pattern.

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