JP6753357B2 - Speed control system for electric motors for rolling mills - Google Patents

Description

The present invention relates to a speed control system for a rolling mill electric motor.

The rolling mills installed in the steel rolling plant are equipped with work rolls for rolling the material to be rolled. The work roll is driven by an AC motor whose speed is controlled by an inverter device. When the tip of the material to be rolled bites into the work roll, an impact load is generated, and there is a problem that the actual speed of the AC motor temporarily drops significantly with respect to the speed standard.

To solve this problem, Patent Document 1 discloses that a predetermined speed raising amount is added to a speed reference when the AC motor is in a no-load state. As a result, it is possible to reduce the speed reduction when an impact load is generated.

Japanese Unexamined Patent Publication No. 2009-153314

On the other hand, when the tail end of the material to be rolled comes off the work roll (so-called tail end coming off, tail coming off), the load decreases sharply, so there is a problem that the actual speed increases significantly with respect to the speed standard of the AC motor. The technique of Patent Document 1 can reduce the speed fluctuation when the material to be rolled is bitten, but cannot reduce the speed fluctuation when the tail end is pulled out.

The present invention has been made to solve the above-mentioned problems, and it is possible to reduce the deviation of the actual speed with respect to the speed reference of the AC motor when the tail end of the material to be rolled is pulled out, and to realize stable speed control. An object of the present invention is to provide a speed control system for an electric motor for a machine.

The speed control system of the electric motor for a rolling mill according to the embodiment of the present invention includes a load cell that outputs a rolling load signal according to a load (rolling load) received from the work roll to be rolled by the work roll that rolls the material to be rolled, and a work roll. It is equipped with an AC motor that drives the rolling mill and an inverter device that converts DC into AC and controls the AC motor at variable speed.

This inverter device includes a speed control unit, an armature current control unit, a tail end omission detection unit, and an armature current compensation circuit unit. The speed control unit calculates a torque reference for matching the actual speed (actual speed) of the AC motor with the speed reference. The armature current control unit calculates the armature current reference (armature current reference) of the AC motor based on the torque reference. The tail end omission detection unit detects the tail end omission in which the tail end of the material to be rolled comes out of the work roll based on the fluctuation of the rolling load signal. The armature current compensation circuit unit outputs a negative armature current compensation value for a certain period of time from the time when the tail end omission is detected. Then, the inverter device supplies AC power to the armature winding of the AC motor based on the compensated armature current reference obtained by adding the negative armature current compensation value to the armature current reference. Preferably, the negative armature current compensation value is set to approach 0 with the passage of time from the time of detection of the tail end omission.

Since the load is suddenly reduced at the timing when the material to be rolled comes out of the work roll, the rolling load signal output by the load cell fluctuates from a predetermined value indicating the rolling state to 0 indicating the rolling end state. The tail end omission detection unit detects the tail end omission from the sudden fluctuation of the rolling load signal. Since the armature current standard is corrected by the negative armature current compensation value for a certain period of time from the detection of tail end omission, the deviation of the actual speed with respect to the speed standard of the AC motor when the load suddenly decreases due to tail end omission of the material to be rolled. Can be reduced. Therefore, a sudden increase in speed of the AC motor is suppressed, and stable speed control can be realized.

Preferably, the AC motor is a synchronous motor, and the inverter device further includes a field current control unit and a field current compensation circuit unit. The field current control unit calculates the field current reference (field current reference) of the field of the synchronous motor based on the magnetic flux reference. The field current compensation circuit unit outputs a negative field current compensation value for a certain period of time from the time when the tail end omission is detected. Then, the inverter device supplies a direct current to the field winding of the synchronous motor based on the compensated field current reference obtained by adding the negative field current compensation value to the field current reference. Preferably, the negative field current compensation value is set to approach 0 with the passage of time from the time when the tail end omission is detected.

For a certain period of time from the detection of tail end omission, the armature current reference is corrected by the negative armature current compensation value, and at the same time, the field current reference is also corrected by the negative field current compensation value. When the load is suddenly reduced due to the tail end coming off, the deviation of the actual speed with respect to the speed standard of the synchronous motor can be reduced. Therefore, a sudden increase in speed of the synchronous motor is suppressed, and stable speed control can be realized.

More preferably, the tail end omission detection unit detects the tail end omission when the actual speed of the AC motor exceeds the set value with respect to the speed reference.

Even in a situation where the rolling load signal of the load cell cannot be normally received, the tail end omission can be detected from the upside of the actual speed with respect to the speed reference. The detection speed of the tail end omission is faster when the tail end omission is detected from the sudden fluctuation of the rolling load signal described above.

According to the speed control system of the electric motor for a rolling mill according to the embodiment of the present invention, it is possible to reduce the deviation of the actual speed with respect to the speed reference of the AC electric motor when the tail end of the material to be rolled is pulled out, and to realize stable speed control.

It is a block diagram of the system which concerns on Embodiment 1 of this invention. It is a figure which shows the speed reference and the speed performance at the time of tail end pulling out of a material to be rolled. It is a block diagram of the inverter control circuit which concerns on Embodiment 1 of this invention. It is a figure which shows the specific example of the negative armature current compensation value at the time of tail end pulling out which concerns on Embodiment 1 of this invention. It is a figure for demonstrating whether or not compensation of an armature current reference at the time of tail end pulling out which concerns on Embodiment 1 of this invention. It is a flowchart for demonstrating the process flow of the inverter control circuit which concerns on Embodiment 1 of this invention. It is a block diagram of the inverter device and the field control part which concerns on Embodiment 2 of this invention. It is a figure which shows the specific example of the negative field current compensation value at the time of tail end pulling out which concerns on Embodiment 2 of this invention. It is a figure for demonstrating whether or not compensation of an armature current reference and a field current reference at the time of tail end pulling out which concerns on Embodiment 2 of this invention. It is a flowchart for demonstrating the process flow of the inverter control circuit which concerns on Embodiment 2 of this invention. It is a figure for demonstrating the detection of the tail end omission of the material to be rolled which concerns on Embodiment 3 of this invention. It is a conceptual diagram which shows the hardware configuration example of the processing circuit (inverter control circuit) which the above-mentioned inverter apparatus 8 has.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The elements common to each figure are designated by the same reference numerals, and duplicate description will be omitted.

Embodiment 1.
[System Configuration of Embodiment 1]
Embodiment 1 of the present invention will be described with reference to FIGS. 1 to 6.

FIG. 1 is a configuration diagram of a system according to a first embodiment of the present invention. The system shown in FIG. 1 is a speed control system for a rolling mill electric motor applied to a steel rolling plant.

The rolling mill 1 shown in FIG. 1 includes a work roll 2, an AC motor 3, a speed sensor 4, and a load cell 5.

The work roll 2 is composed of a pair of rolls, and the material 6 to be rolled is rolled according to the roll gap. The material 6 to be rolled is a metal material and is conveyed from the left side to the right side in FIG. 1 while being rolled on the work roll 2. Further, the rotating shaft of the work roll 2 is connected to the rotating shaft of the AC motor 3.

The AC motor 3 is driven by three-phase AC to rotate the work roll 2. As an example, the AC motor 3 is a synchronous motor. The armature is arranged as a stator coil (armature winding) on the fixed side, and the field is arranged as a rotor coil (field winding) on the rotating side. The armature may be a rotor and the field may be a stator. In the present embodiment, the AC motor 3 may be an induction motor. Further, it is not limited to three-phase alternating current, and may be single-phase alternating current or multi-phase alternating current.

The speed sensor 4 is arranged near the rotation axis of the AC motor 3 and outputs a speed feedback signal according to the rotation speed (actual speed) of the AC motor 3.

The load cell 5 is provided in the vicinity of the work roll 2 and outputs a rolling load signal according to the load received by the work roll 2 from the material 6 to be rolled (hereinafter referred to as a rolling load).

The programmable logic controller (hereinafter referred to as PLC) 7 outputs a rolling load signal received from the load cell 5 and a speed reference of the AC motor 3 according to the rolling conditions of the material 6 to be rolled for each control cycle.

The inverter device 8 converts direct current into alternating current to control the alternating current motor 3 at a variable speed. The inverter device 8 receives a rolling load signal, a speed reference, a speed feedback signal, etc. for each control cycle, and supplies electric power to the AC motor 3 so that the actual speed (actual speed) of the AC motor 3 matches the speed reference. Supply.

FIG. 2 is a diagram showing a speed reference and a speed record when the tail end of the material 6 to be rolled is pulled out. The broken line 10 indicates the speed reference SP_R. The solid line 11 shows the actual speed SP_F. The time t0 indicates the time when the material 6 to be rolled comes out of the work roll 2 at the tail end.

When the material 6 to be rolled comes out of the work roll 2 at time t0, the load torque suddenly decreases, so that the actual speed SP_F increases with respect to the speed reference SP_R of the AC motor 3. By the speed feedback control, the deviation between the speed reference SP_R and the speed actual SP_F disappears after a predetermined time elapses. However, from the viewpoint of stability of speed control, it is desirable that the actual speed SP_F follows the speed reference SP_R earlier.

(Block diagram of inverter device 8)
In order to solve such a problem, the inverter device 8 according to the present embodiment is configured as shown in FIG. FIG. 3 is a block diagram for explaining the function of the inverter device 8 according to the first embodiment of the present invention. The inverter device 8 includes an inverter that converts direct current and alternating current to drive the AC motor 3 and an inverter control circuit that controls the output of the inverter. The main circuit of the inverter control circuit includes a speed control unit 20, an armature current control unit 21, a tail end missing detection unit 22, an armature current compensation circuit unit 23, an armature voltage control unit 24, and a PWM controller 25. The voltage type inverter element 26 is a switching element constituting the inverter.

The speed control unit 20 calculates a torque reference for matching the actual speed (actual speed) of the AC motor 3 with the speed reference. Specifically, the speed control unit 20 inputs the difference between the speed reference and the speed feedback signal detected by the speed sensor 4 from the outside (PLC7), and calculates the torque reference for making the difference 0.

The armature current control unit 21 calculates the armature current reference (hereinafter referred to as armature current reference) of the armature of the AC motor 3 based on the torque reference.

The inverter device 8 according to the present embodiment includes a tail end missing detection unit 22 for monitoring the rolling state and an armature current compensation circuit unit 23 as main features.

The tail end omission detection unit 22 detects the tail end omission in which the tail end of the material 6 to be rolled comes out of the work roll 2 based on the fluctuation of the rolling load signal. Since the load suddenly decreases at the timing of the tail end coming off, the rolling load signal output by the load cell 5 changes from a predetermined value indicating the state during rolling to 0 indicating the rolling end state. The tail end omission detection unit 22 detects the tail end omission from the sudden fluctuation of the rolling load signal.

The armature current compensation circuit unit 23 outputs a negative armature current compensation value for a certain period of time from the time when the tail end omission is detected. Preferably, the negative armature current compensation value is set to approach 0 with the passage of time from the time of detection of the tail end omission.

FIG. 4 is a diagram showing a specific example of a negative armature current compensation value when the tail end is pulled out according to the first embodiment of the present invention. The armature current compensation circuit unit 23 outputs a negative armature current compensation value for a certain period of time (compensation section) from the time t0 when the tail end is pulled out. The negative armature current compensation value is maximum when the tail end is missing (time t0), decreases with the passage of time, and becomes 0 after a certain period of time (time t1).
The fixed time (compensation section) can be set arbitrarily.

The armature current reference output by the armature current control unit 21 is corrected (reduced) by the negative armature current compensation value output by the armature current compensation circuit unit 23 for a certain period of time from the time when the tail end is detected. The compensated armature current reference obtained by adding the negative armature current compensation value to the armature current reference is input to the armature voltage control unit 24.

The armature voltage control unit 24 calculates the armature voltage reference (hereinafter referred to as armature voltage reference) of the AC motor 3 based on the armature current reference after compensation.

The PWM controller 25 creates a gate pulse by PWM control based on the armature voltage reference. The voltage-type inverter element 26, which is a switching element, is controlled on and off by a gate pulse, and the inverter device 8 supplies AC power to the armature winding 3a of the AC motor 3.

FIG. 5 is a diagram for explaining whether or not compensation is provided based on the armature current when the tail end is pulled out according to the first embodiment of the present invention. The solid line 40 represents the armature current reference when there is no compensation, and the broken line 41 represents the armature current reference when there is compensation. By correcting the armature current reference with the negative armature current compensation value shown in FIG. 4 at each time of the compensation section, it is possible to suppress the fluctuation of the current reference after the tail end is removed as shown by the broken line 41. .. As a result, the speed fluctuation of the AC motor 3 can be suppressed.

(Processing flow of inverter control circuit)
FIG. 6 is a flowchart for explaining the processing flow of the inverter control circuit according to the first embodiment of the present invention. The routine shown in FIG. 6 is repeatedly executed every control cycle. At the first execution, the value of t is set to n (n: indicating the end of the compensation interval). At the second and subsequent executions, the value of t in the previous routine is inherited.

First, in step S100, the inverter control circuit inputs the speed reference and the rolling load signal in the current control cycle from the PLC 7, and inputs the speed feedback signal from the speed sensor 4.

Next, in step S105, the speed control unit 20 calculates a torque reference for making the difference between the speed reference and the speed feedback signal 0.

Next, in step S110, the armature current control unit 21 calculates the armature current reference based on the torque reference.

Further, in step S115, the tail end omission detection unit 22 determines whether or not the tail end omission has occurred based on the fluctuation of the rolling load signal. When the timing at which the tail end omission is detected, the process proceeds to step S120, and in other cases, that is, when rolling is in progress or after the end of rolling (at the time of tail end omission), the process proceeds. The process proceeds to step S145.

When the tail end omission is detected, in step S120, the time counter t indicating the elapsed time after the tail end omission is initialized to 0.

In step S125, the armature current compensation circuit unit 23 outputs a negative armature current compensation value for a certain period of time from the time when the tail end omission is detected. Specifically, as shown in FIG. 4, a negative armature current compensation value corresponding to the value of the time counter t is output.

In step S130, the negative armature current compensation value calculated in step S125 is added to the armature current reference calculated in step S110 to calculate the armature current reference after compensation. In step S135, the armature voltage control unit 24 calculates the armature voltage reference based on the compensated armature current reference. In step S140, the voltage type inverter element 26 is controlled by a gate pulse according to the armature voltage reference.

After that, the value of the time counter t is taken over, and this routine is executed in the next control cycle. In the next control cycle, since the tail end omission has already occurred, the determination condition in step S115 is not satisfied, and the process proceeds to step S145.

In step S145, the tail end omission detection unit 22 determines whether or not the value of the time counter t has reached n. Until the value of the time counter t reaches n, the process proceeds to step S150. In step S150, the time counter t is incremented, and in the processing after step S150, the armature current reference is corrected by the negative armature current compensation value based on the new time counter t. On the other hand, in step S145, when the value of the time counter t reaches n, a certain time (compensation section) has elapsed from the time when the tail end omission is detected, so that the correction of the armature current reference ends.

As described above, according to the routine shown in FIG. 6, when the load is suddenly reduced due to the tail end of the material 6 to be rolled, the deviation of the actual speed with respect to the speed reference of the AC motor 3 can be reduced, and stable speed control can be realized. ..

By the way, in the inverter device 8 of the first embodiment described above, a voltage type inverter is used, but the present invention is also applicable to a current type inverter. This point is the same in the following embodiments.

(Hardware configuration example of inverter control circuit)
FIG. 12 is a conceptual diagram showing a hardware configuration example of the processing circuit (inverter control circuit) included in the above-mentioned inverter device 8. Each part in FIG. 3 (and FIG. 7 described later) shows a part of the function, and each function is realized by a processing circuit. In one aspect, the processing circuit comprises at least one processor 91 and at least one memory 92. In another aspect, the processing circuit comprises at least one dedicated hardware 93.

When the processing circuit includes a processor 91 and a memory 92, each function is realized by software, firmware, or a combination of software and firmware. At least one of the software and firmware is written as a program. At least one of the software and firmware is stored in memory 92. The processor 91 realizes each function by reading and executing the program stored in the memory 92.

When the processing circuit includes dedicated hardware 93, the processing circuit is, for example, a single circuit, a composite circuit, a programmed processor, or a combination thereof. Each function is realized by a processing circuit.

Embodiment 2.
[System Configuration of Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIGS. 7 to 10. The system of this embodiment can be realized by causing the inverter control circuit to execute the routines of FIG. 6 and FIG. 10 described later in the configurations shown in FIGS. 1 and 7. Hereinafter, the points different from those of the first embodiment will be mainly described. In the second embodiment, the AC motor 3 is a synchronous motor.

(Block diagram of inverter device 8)
FIG. 7 is a block diagram for explaining the function of the inverter device 8 according to the second embodiment of the present invention. In the second embodiment, the inverter control circuit includes a field circuit in addition to the main circuit of FIG. 3 described above. The field circuit includes a field current control unit 27, a field current compensation circuit unit 28, a field voltage control unit 29, and a phase controller 30. The thyristor element 31 is a switching element that constitutes a rectifier for supplying a direct current to the field winding 3b.

The field current control unit 27 calculates the field current reference (hereinafter referred to as the field current reference) of the AC motor 3 based on the magnetic flux reference. The tail end omission detection unit 22 described above is connected to the field current compensation circuit unit 28 in addition to the armature current compensation circuit unit 23, and the signal at the time of tail end omission detection is transmitted to both.

The field current compensation circuit unit 28 outputs a negative field current compensation value for a certain period of time from the time when the tail end omission is detected. Preferably, the negative field current compensation value is set to approach 0 with the passage of time from the time when the tail end omission is detected.

FIG. 8 is a diagram showing a specific example of the negative field current compensation value when the tail end is missing according to the first embodiment of the present invention. The field current compensation circuit unit 28 outputs a negative field current compensation value for a certain period of time (compensation section) from the time t0 when the tail end is removed. The negative field current compensation value is maximum when the tail end is missing (time t0), decreases with the passage of time, and becomes 0 after a certain period of time (time t1). The fixed time (compensation section) is the same as the compensation section shown in FIG. The field current compensation value shown in FIG. 8 and the armature current compensation value shown in FIG. 4 are different in magnitude.

The field current reference output by the field current control unit 27 is corrected (reduced) by the negative field current compensation value output by the field current compensation circuit unit 28 for a certain period of time from the time when the tail end is detected. The field current reference after compensation obtained by adding the negative field current compensation value to the field current reference is input to the field voltage control unit 29.

The field voltage control unit 29 calculates the field voltage reference (hereinafter referred to as the field voltage reference) of the AC motor 3 based on the field current reference after compensation.

The phase controller 30 creates a gate pulse by phase control based on a field voltage reference. The thyristor element 31 is on / off controlled by a gate pulse, and the inverter device 8 supplies a direct current to the field winding 3b of the AC motor 3.

FIG. 9 is a diagram for explaining whether or not compensation is provided for the armature current reference and the field current reference when the tail end is missing according to the second embodiment of the present invention. The solid line 40 represents the armature current reference when there is no compensation, and the broken line 41 represents the armature current reference when there is compensation, which is the same as in FIG. The solid line 42 represents the field current reference without compensation, and the broken line 43 represents the field current reference with compensation. By correcting the field current reference with the negative field current compensation value shown in FIG. 8 at each time of the compensation section, it is possible to suppress the fluctuation of the current reference after the tail end is removed as shown by the broken line 43. .. As a result, the speed fluctuation of the AC motor 3 can be suppressed.

(Processing flow of inverter control circuit)
In the second embodiment, the inverter control circuit executes the field control routine shown in FIG. 10 at the same time as the armature control routine shown in FIG. 6 described above. The routine shown in FIG. 10 is repeatedly executed every control cycle. At the first execution, the value of t is set to n (n: indicating the end of the compensation interval). At the second and subsequent executions, the value of t in the previous routine is inherited.

First, in step S200, the inverter control circuit inputs the magnetic flux reference and the rolling load signal in the current control cycle.

Next, in step S205, the field current control unit 27 calculates the field current reference based on the magnetic flux reference.

Further, in step S210, the tail end omission detection unit 22 determines whether or not the tail end omission has occurred based on the fluctuation of the rolling load signal. When the timing at which the tail end omission is detected, the process proceeds to step S215, and in other cases, that is, when rolling is in progress or after the end of rolling (at the time of tail end omission), the process proceeds. The process proceeds to step S240.

When the tail end omission is detected, in step S215, the time counter t indicating the elapsed time after the tail end omission is initialized to 0.

In step S220, the field current compensation circuit unit 28 outputs a negative field current compensation value for a certain period of time from the time when the tail end omission is detected. Specifically, as shown in FIG. 8, a negative field current compensation value corresponding to the value of the time counter t is output.

In step S225, the negative field current compensation value calculated in step S220 is added to the field current reference calculated in step S205 to calculate the compensated field current reference. In step S230, the field voltage control unit 29 calculates the field voltage reference based on the compensated field current reference. In step S235, the thyristor element 31 is controlled by a gate pulse according to the field voltage reference.

After that, the value of the time counter t is taken over, and this routine is executed in the next control cycle. In the next control cycle, since the tail end omission has already occurred, the determination condition in step S210 is not satisfied, and the process proceeds to step S240.

In step S240, the tail end omission detection unit 22 determines whether or not the value of the time counter t has reached n. Until the value of the time counter t reaches n, the process proceeds to step S245. In step S245, the time counter t is incremented, and in the processing after step S245, the field current reference is corrected with a negative field current compensation value based on the new time counter t. On the other hand, in step S240, when the value of the time counter t reaches n, a certain time (compensation section) has elapsed from the time when the tail end omission is detected, so that the correction of the field current reference is completed.

As described above, according to the routine shown in FIG. 10, the armature current reference is corrected by the negative armature current compensation value by the routine of FIG. 6 for a certain period of time from the time of detecting the tail end omission, and at the same time, the field Since the current reference is also corrected by the negative field current compensation value, it is possible to reduce the deviation of the actual speed with respect to the speed reference of the synchronous motor when the load is suddenly reduced due to the tail end of the material 6 to be rolled. Therefore, a sudden increase in speed of the synchronous motor is suppressed, and stable speed control can be realized.

Embodiment 3.
[System Configuration of Embodiment 3]
Next, a third embodiment of the present invention will be described with reference to FIG. The system of the present embodiment is realized by adding a process described later to the tail end omission detection unit 22 of the first or second embodiment. Hereinafter, the points different from those of the second embodiment will be mainly described.

As described in the first embodiment, it is desirable to detect the tail end omission of the material 6 to be rolled from the fluctuation of the rolling load signal of the load cell from the viewpoint of the detection speed. However, there may be a situation where the rolling load signal of the load cell cannot be received normally. Therefore, the tail end omission detection unit 22 according to the present embodiment adds a process of detecting the tail end omission when the actual speed (actual speed) of the AC motor 3 exceeds the set value with respect to the speed reference. did.

As shown in FIG. 11, even if there is no change in the speed reference, the tail end omission due to the end of rolling can be detected by increasing the actual speed based on the speed feedback signal output by the speed sensor 4 by a certain amount or more. When the tail end omission is detected, a correction is performed to reduce the armature current reference and the field current reference, as in the first and second embodiments.

According to the tail end omission detection unit 22 according to the third embodiment, the tail end omission can be detected from the upside of the actual speed with respect to the speed reference. Therefore, even in a situation where the rolling load signal of the load cell cannot be normally received, it is possible to reduce the deviation of the actual speed with respect to the speed reference of the AC motor and realize stable speed control.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be variously modified and implemented without departing from the spirit of the present invention.

1 Roller 2 Work roll 3 AC motor 3a Armature winding 3b Field winding 4 Speed sensor 5 Load cell 6 Material to be rolled 7 PLC
8 Inverter device 20 Speed control unit 21 Armature current control unit 22 Tail end omission detection unit 23 Armature current compensation circuit unit 24 Armature voltage control unit 25 PWM controller 26 Voltage type inverter element 27 Field current control unit 28 Field Current compensation circuit unit 29 Field voltage control unit 30 Phase controller 31 Cylister element

Claims (5)

A load cell that outputs a rolling load signal according to the load received by the work roll that rolls the material to be rolled from the material to be rolled, and
The AC motor that drives the work roll and
Equipped with an inverter device that converts direct current to alternating current and controls the AC motor at variable speed.
The inverter device is
A speed control unit that calculates a torque reference for matching the actual speed of the AC motor with the speed reference,
An armature current control unit that calculates an armature current reference (hereinafter referred to as an armature current reference) of the AC motor based on the torque reference.
A tail end omission detection unit that detects a tail end omission in which the tail end of the material to be rolled comes out of the work roll based on the fluctuation of the rolling load signal.
It is provided with an armature current compensation circuit unit that outputs a negative armature current compensation value for a certain period of time from the time when the tail end omission is detected.
Supplying AC power to the armature winding of the AC motor based on the compensated armature current standard obtained by adding the negative armature current compensation value to the armature current reference.
A speed control system for electric motors for rolling mills. The negative armature current compensation value approaches 0 with the passage of time from the detection of the tail end omission.
The speed control system for an electric motor for a rolling mill according to claim 1. The AC motor is a synchronous motor and
The inverter device is
A field current control unit that calculates the field current reference (hereinafter referred to as the field current reference) of the synchronous motor based on the magnetic flux reference.
A field current compensation circuit unit that outputs a negative field current compensation value for a certain period of time from the time when the tail end omission is detected is further provided.
Supplying a direct current to the field winding of the synchronous motor based on the compensated field current reference obtained by adding the negative field current compensation value to the field current reference.
The speed control system for an electric motor for a rolling mill according to claim 1 or 2. The negative field current compensation value approaches 0 with the passage of time from the time when the tail end omission is detected.
The speed control system for an electric motor for a rolling mill according to any one of claims 1 to 3. The tail end omission detection unit detects the tail end omission when the actual speed of the AC motor exceeds the set value with respect to the speed reference.
The speed control system for an electric motor for a rolling mill according to any one of claims 1 to 4.

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