JP2759591B2 - Rolling control system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling plant and, more particularly, to a rolling control system for a large-scale rolling plant having a plurality of rolling systems.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a rolling control system. Rolling is performed every time a rolling mill called a plurality of stands is arranged in series and continuously passes through the stands. In the figure, reference numeral 501 denotes a heating furnace equipment for heating a material to be rolled;
02 is a press device for adjusting the width of the rolled material, 503 is a rough rolling machine for performing rough rolling, 504 is an edger equipment for finishing the width, 505 is a finishing rolling machine for performing finishing rolling, 50
6 is a cooling device, and 507 is a coiler device for winding the finished rolled material. The efficiency of these rolling equipment is increased by increasing the speed and speed of the rolling equipment. Therefore, the upstream rough rolling mill 503 is required to have a large-capacity and high-efficiency motor drive system since the material is reduced from a state where the material is still thick to a state where the material is close to the finish. The downstream finishing mill 505 requires a motor drive system with low motor torque ripple to ultimately affect the quality of the finished product. Further, in order to improve the quality, it is necessary to control the tension between the stands to be constant, and it is desired that the output of the electric motor has no torque ripple. Here, FIGS. 6 and 7 show a conventional rolling control system to which a power converter is applied. FIG.
Is a rolling control system to which a cycloconverter is applied.
This is a rolling control system in which a cycloconverter is applied to a main motor drive device. In the figure, 611 to 615 are cyclo converters, 601 to 605 are large capacity transformers, 62
1 to 625 are main motor drive devices. Since the cycloconverter can raise the power factor to only about 0.5 in principle, a large capacity transformer and a reactive power compensator (static bar compensator;
(Hereinafter referred to as SVC) 630. HF
Indicates a capacitor. Incidentally, a mechanism for absorbing reactive power of the load by the SVC, as shown in FIG. 8, a current i _C proceeds equal to delay current i _L generated from the load generated from SVC, thereby canceling the delay current i _L. As a result, only the effective current i _S flows through the power supply, and the power factor 1
Will be able to drive. In addition, since the power factor of the cycloconverter also changes depending on the rolling speed, to control the power factor always constant, monitor the power factor while monitoring the power factor.
You need to control this. Therefore, the SVC also needs to dynamically control the power factor, and requires an expensive device having a converter such as an active filter.
In addition, the SVC performs an operation of generating a large amount of reactive power when the load is not operating, and a loss occurs even when the equipment is stopped such as during a no-load operation. However, the efficiency of the system as a whole decreases. FIG. 7 shows a rolling control system to which a GTO (gate turn-off thyristor) power converter is applied.
In the figure, 711 to 715 are GTOs, 701 to 705 are large-capacity transformers, and 721 to 725 are main motor drive devices. GTO is also a rolling equipment aiming at high responsiveness and maintenance-free. Since the GTO converter can arbitrarily control the power factor of the power supply, it can be operated at a power factor of 1 without equipment such as SVC and can be said to be a clean power converter, but the torque ripple is large in the motor output. There is a problem. By the way, as an example in which a cycloconverter is employed in a rolling control system, see Japanese Patent Application Laid-Open No. 3-147115.
There is a number. This rolling control system generates a large amount of reactive power and requires a large phase advance capacitor to compensate for this. In this type of system, the system voltage changes under the influence of the no-load reactive power generated by the constant connection of a large-capacity phase-advancing capacitor. For this purpose, it is necessary to connect and disconnect a capacitor connected to the system, or to generate reactive power intentionally to compensate for the voltage fluctuation. However, when connecting and disconnecting a capacitor, a large rush current flows, which causes the voltage of the system to fluctuate, and intentionally generating reactive power is a power loss and does not save energy.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to apply a motor drive system to a rolling mill and to require a special reactive power compensator in consideration of the characteristics of a cycloconverter and a GTO power converter. It is another object of the present invention to provide a high-efficiency and high-power-factor rolling control system.

[0004]

SUMMARY OF THE INVENTION In a rolling plant having a plurality of AC motors and a power converter for driving the AC motor, the rolling plant has the following power converters:
A pulse width modulation converter / inverter that converts a DC voltage to AC power and controls a power factor, and a cycloconverter or a power device with a poor power factor are simultaneously applied to absorb the reactive power of the cycloconverter or the power device. I do.

[0005]

A cycloconverter and a pulse width modulation converter / inverter are applied to a rolling plant comprising a plurality of rolling systems, a cycloconverter is applied to a rolling equipment requiring a high degree of torque control, and PW is simultaneously applied to other rolling equipment.
Apply M and control the power factor without applying a special reactive power compensator. As a result, a highly efficient and high power factor rolling control system is realized. In addition, not only the cycloconverter but also other power supply equipment having a bad power factor can be similarly provided by applying the pulse width modulation converter / inverter.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a rolling control system according to an embodiment of the present invention.
12, 116, 117 and 118 are GTO power converters,
Reference numerals 114, 115, 119 and 120 denote cycloconverters, and 121 to 130 denote AC motors, respectively. This rolling control system is a system for rolling a material that is still red hot and is called a hot rolling control system. A rough rolling system (stands R1, R2, R3) for rolling a thick material under high pressure. ) And finish rolling system (Stands F1, F2, F3, F4,
F5, F6, F7).

Here, the configuration of the cycloconverter is shown in FIG.
Next, FIG. 4 shows the configuration of a GTO power converter, and each feature will be described. In FIG. 3, the equipment configuration of the cycloconverter includes a transformer 301 and a cycloconverter 30.
2, consisting of a switch 303 and an AC motor IM304,
The cyclo converter has the following features. Feature (1): Output torque waveform has little ripple. For this reason, highly accurate tension control is possible. Feature (2): Limited by the commutation angle of the thyristor,
There is a control range of the output frequency only from the frequency of 1/2 to 1/3 of the power supply frequency. In addition, since many thyristor elements are used, the number of transformers 301 for power supply is increased, so that a large amount of space and wiring are required, and power loss in operation is large. Furthermore, since the reactive power is large due to the poor operating power factor, the capacity of the power supply system becomes excessive, and the power supply equipment with large voltage fluctuations becomes large, so a large space is required when adding to the existing equipment. . Equipment that does not have sufficient power needs an SVC to improve the power factor. On the other hand, SVC has a problem that the power loss at the time of no load is large. In FIG. 4, the power converter of the GTO is a system in which AC power is converted into DC power by a converter at one end, and is converted into AC by an inverter.
1, GTO converter / inverter 402, switch 4
03, comprising an AC motor IM404. The GTO converter / inverter has the following features. Features (1): The GTO can generate a higher frequency than the cycloconverter, and the power factor of the converter on the power supply side can be controlled to 1 so that the power of the capacity of the equipment is sufficient. There is an advantage that it can be easily added to existing equipment. The number of transformers that supply power is also small, and the space for power supply equipment is very small as compared with a cycloconverter.
Furthermore, since the GTO converter can arbitrarily control the phase of the voltage and current on the converter side, it is also possible to control this phase by the power factor of the power source and control the power factor of the power source. Since no SVC equipment is required, overall efficiency is high. Feature (2): The torque ripple is larger in the motor output than in the cyclo converter.

In FIG. 1, the stands R1, R2, and R3 of the rough rolling system require rolling power performance due to the accuracy of the product thickness, and perform a very overload operation. As a result, a reactive current is generated. So, GTO
Due to the features of the converter / inverter, the GTO that can control the power factor of the power supply is equipped with a stand R for the rough rolling system.
1, applied to R2 and R3 to suppress generation of reactive current.
On the other hand, the stands F1, F2, F of the finishing rolling system
3, F4, F5, F6, and F7 determine the accuracy of the final product, and high-precision rolling with little disturbance is required. As a feature of rolling, the product has the property that it undergoes work hardening while being rolled at each stand and is less susceptible to disturbance. Therefore, considering this characteristic,
Due to the features of the cycloconverter, a cycloconverter with less torque disturbance is applied to the stands F1 and F2 at the preceding stage of the finish rolling system. Middle stand F
In 3, F4 and F5, the torque disturbance is absorbed by the tension control of the rolling mill, so that the influence on the material is hardly caused. Therefore, a GTO with a high power factor is applied here. Since the final stage stands F6 and F7 determine the product quality,
Use a cycloconverter with less disturbance. As a result, a highly accurate product can be manufactured. However, when a cycloconverter is applied, reactive power is generated, and disadvantages such as a voltage fluctuation and an increase in power supply capacity arise, and a special device (SVC) for compensating for this is required. However, in this rolling control system, by simultaneously applying the GTO, the power factor of the power receiving side is monitored, the power factor of the GTO converter is controlled, and the reactive power generated from the cycloconverter is specially invalidated. Improve the power factor without using a power compensator.
FIG. 2 illustrates the principle of improving the power factor. In FIG.
Stands F1, F2 at the front stage of the finish rolling system of FIG.
And the state of generation of reactive power by the cycloconverters of the last stands F6, F7 and the GTO applied to the stands R1, R2, R3 of the rough rolling system and the middle stands F3, F4, F5 of the finishing rolling system. This shows a state in which the reactive power is compensated.

In this embodiment, the GTO converter / inverter of the rough rolling system and the GTO converter / inverter of the finishing rolling system are used, and the power factor at the power receiving point (point A in FIG. 1) is reduced. The power factor of each GTO converter is controlled so as to reach a target value. This will be described in detail below. Preceding stand F1 of the finish rolling system, F2 and the final stage of the stand F6, F7 power each _{F 1, F 2, F 6} , F 7 KV
A, and the power factors are COS θ ₁ , COS θ ₂ , and COS, respectively.
Assuming that θ ₃ and COS θ ₄ , the total amount of reactive power A ₁ of the cycloconverter is obtained by setting the capacity of each GTO converter to R ₁ , R ₂ ,
As R ₃ , F ₃ , F ₄ , F ₅ KVA, A ₁ = F ₁ SINθ ₁ + F ₂ SINθ ₂ + F ₆ SINθ ₃ + F ₇
The SINθ _4. The power commensurate with the total amount A ₁ of this reactive power GTO
By controlling the power factor, to generate electric power becomes -A _1, controls the power factor for the entire system. Where A ₂ is GT
Assuming that the reactive power amount compensated by O, A ₂ = R ₁ SINα ₁ + R ₂ SINα ₂ + R ₃ SINα ₃ + F ₃
SINα ₄ + F ₄ SINα ₅ + F ₅ SINα ₆ Therefore, if the phase of the current and voltage of the GTO converter is controlled so that A ₁ + A ₂ = 0, the reactive power can be made zero. The capacity KW required for the power supply is B ₁ = F ₁ COS θ ₁ + F ₂ COS θ ₂ + F ₆ COS θ ₃ + F _{7 at the} cycloconverter side.
B ₂ = R ₁ COS α ₁ + R ₂ COS α ₂ + R ₃ COS α ₃ + F ₃ on the CTO θ ₄ GTO side
COSα ₄ + F ₄ COSα ₅ + F ₅ COSα ₆ , and B ₁ + B _{2 as} a whole. As described above, since the power supply power factor can be made 1 by controlling the phase of the GTO converter, the KVA required for the power supply is B
Can be the same value as ₁ + B _2, thereby the power to a minimum. Therefore, it is possible to realize the maximum rolling control system with the minimum capacity and the minimum equipment even in the business place where the power source is weak. In FIG. 1, the GTO
Although the converters of the converter / inverter are independent for each stand, the same applies if they are integrated as a common converter. In addition, in the present invention, the same function is exhibited by applying the pulse width modulation converter / inverter, even when employing not only the cycloconverter but also other power supply equipment having a low power factor.

[0010]

As described above, according to the present invention,
A special reactive power compensator by using a cycloconverter and a GTO power converter together in the motor drive system of the rolling equipment, combining the characteristics of each and adapting it to the control characteristics of the rolling equipment. , And high efficiency and high power factor rolling control can be realized. In addition, by using a cycloconverter and a GTO power converter together, the power supply power factor can be controlled to 1 so that it is sufficient if there is enough power for the capacity of the equipment. In addition, the number of transformers for supplying electric power is small, and the space for the power supply equipment can be extremely reduced. Furthermore, GT
Since the power converter of O can arbitrarily control the phase of the voltage and the current, it is possible to control this phase by the power factor of the power source and to control the power source power factor, and the reactive power compensating device is unnecessary. Therefore, overall efficiency is improved. Moreover, since the cycloconverter has a small ripple in the output torque waveform of the electric motor, high-accuracy tension control can be performed in the rolling system.

[Brief description of the drawings]

FIG. 1 is an embodiment of the present invention, a rolling control system having a rough rolling system and a finishing rolling system.

FIG. 2 is a diagram showing a state in which a reactive power is generated by a cycloconverter and a state in which the reactive power is compensated by a GTO.

Fig. 3 Cycloconverter equipment configuration

[Fig. 4] Device configuration of GTO converter / inverter

FIG. 5 shows an example of a rolling control system.

FIG. 6 is a rolling control system to which a conventional cycloconverter is applied.

FIG. 7 is a rolling control system to which a conventional GTO converter / inverter is applied.

FIG. 8 is a diagram showing a concept of reactive power compensation using SVC.

[Explanation of symbols]

101-110 Large-capacity transformers 111, 112, 116, 117, 118 GTO power converters 114, 115, 119, 120 Cycloconverters 121-130 AC motors R1, R2, R3 Stands for rough rolling system F1, F2, F3, F4, F5, F6, F7 Finish rolling system stand

Claims (4)

(57) [Claims] In a rolling plant having a plurality of AC motors and a power converter for driving the AC motor, the rolling plant converts a DC voltage into AC power and controls a power supply power factor as the power converter. A pulse width modulation converter / inverter (hereinafter referred to as PWM);
A rolling control system characterized by simultaneously applying a cycloconverter or a power supply facility having a low power factor to absorb reactive power of the cycloconverter or the power supply facility. 2. In a rolling plant having a plurality of AC motors and a power converter for driving the AC motors, a cycloconverter or a power supply with a poor power factor is applied to a rolling equipment requiring a high degree of torque control, A rolling control system, wherein a PWM for controlling a power factor is applied to a rolling facility according to (1). 3. The rolling plant according to claim 1, wherein the rolling plant has a rough rolling facility and a finishing rolling facility, wherein one or more PWMs are applied to the rough rolling facility, and one of the finishing rolling facilities is applied. A rolling control system, wherein a plurality of cycloconverters are simultaneously applied to improve a power supply power factor by the PWM phase control, and the cycloconverter performs an operation with little torque ripple on an output of a motor. 4. The rolling plant according to claim 1, wherein the rolling plant has a rough rolling facility and a finish rolling facility, wherein PWM is applied to the rough rolling facility and the finishing rolling facility. A rolling control system in which a cycloconverter is applied to a first stage and a last stage to improve a power supply power factor by controlling the phase of the PWM, and the cycloconverter performs an operation with little torque ripple on the output of the electric motor.