JPH06198318A - System for controlling rolling - Google Patents

Abstract

PURPOSE:To obtain a high-efficiency and high power-factor system for controlling rolling by simultaneously applying a pulse-width modulation convertor/ inverter and a cycloconverter or power-supply installation of low power-factor and absorbing reactive power. CONSTITUTION:This system is a rolling plant having plural AC motors 121-130 and power converters (GTO) 111-118 with which the AC motors are driven. As a power converter in this rolling plant, the pulse-width modulation converter/ inverter (PWM) with which DC voltage is converted into AC power and also the power-factor of a power-supply is controlled and a cycloconverter (CYC) or the power-supply installation of low power-factor are simultaneously applied and the reactive power of the cycloconverter or the power-supply installation is absorbed In this way, the phase is controlled by the power-factor of the power-supply, the power-factor of the power-supply is controlled and the efficiency is improved because a reactive power compensator is unnecessitated.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art An example of a rolling control system is shown in FIG. Rolling is performed by arranging a plurality of rolling machines called stands in series and continuously passing through the stands. In the figure, 501 is a heating furnace facility for heating the material to be rolled, 5
Reference numeral 02 is a press device for adjusting the width of the rolled material, 503 is a rough rolling machine for rough rolling, 504 is an edger equipment for finishing the width, 505 is a finish rolling machine for finish rolling, 50
6 is a cooling device, and 507 is a coiler device for winding the finished rolled material. These rolling equipments have improved efficiency by being continuous and speeding up. Therefore, the rough rolling mill 503 on the upstream side rolls down the material from a state where the material is still thick to a state where it is close to finishing, and therefore a large-capacity, high-efficiency motor drive system is required. The finish rolling mill 505 on the downstream side needs an electric motor drive system in which the torque ripple of the motor is small in order to finally 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, a conventional rolling control system to which a power converter is applied is shown in FIGS. 6 and 7. Figure 6
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 cycloconverters, 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 is required. In addition, HF
Indicates a capacitor. As shown in FIG. 8, the mechanism for absorbing the reactive power of the load by the SVC causes the SVC to generate a lead current i _C equal to the lag current i _L generated from the load, thereby canceling the lag current i _L. As a result, only the effective current i _S flows to the power source, and the power factor is 1
Will be able to drive. The power factor of the cycloconverter also changes depending on the rolling speed, so to control the power factor to be constant at all times, monitor the power factor of the power supply.
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 operates so as to generate a large amount of reactive power when the load is not operating, which means that loss occurs even when the equipment is at rest, such as during no-load operation. , The efficiency of the entire system is poor. 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. The GTO is also a rolling facility aiming at high responsiveness and maintenance-free. The GTO converter can control the power source power factor arbitrarily, so it can be operated at a power factor of 1 without any equipment such as an SVC, and it can be said that it is a clean power converter, but it has a large torque ripple in the motor output. There is a problem. By the way, as an example of adopting a cycloconverter in a rolling control system, Japanese Patent Laid-Open No. 3-147115
There is an issue. This rolling control system generates a large reactive power and also requires a large phase advance capacitor to compensate for it. In this type of system, the system voltage changes under the influence of the reactive power at the time of no load, which is generated by the constant connection of the large-capacity phase-advancing capacitor. For this reason, it is necessary to connect a capacitor connected to the system and disconnect it, or to intentionally generate reactive power to compensate for voltage fluctuations. However, when connecting and disconnecting the capacitor, a large inrush current flows, which in turn changes the voltage of the system, and intentionally generating reactive power is a power loss and does not save energy.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to apply a motor drive system to a rolling mill by considering the respective characteristics of a cycloconverter and a GTO power converter and requiring a special var compensator. In other words, it is to provide a rolling control system with high efficiency and high power factor.

[0004]

In a rolling plant having a plurality of AC electric motors and a power converter for driving the AC electric motors, the rolling plant has the electric power converters,
A pulse width modulation converter / inverter that converts a DC voltage into an AC power and controls a power supply power factor and a cycloconverter or a power supply facility with a poor power factor are simultaneously applied to absorb reactive power of the cycloconverter or the power supply facility. To do.

[0005]

The cycloconverter and the pulse width modulation converter / inverter are applied to a rolling plant consisting of a plurality of rolling systems, the cycloconverter is applied to rolling equipment that requires high torque control, and at the same time PW is applied to other rolling equipment.
Apply M and control the power supply power factor without applying a special reactive power compensator. This realizes a rolling control system with high efficiency and high power factor. Further, not only the cycloconverter, but also the other power supply equipment having a poor power factor can be similarly applied by similarly applying the pulse width modulation converter / inverter.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a rolling control system showing an embodiment of the present invention, in which 101 to 110 are large capacity transformers, 111 and 1
12, 116, 117 and 118 are GTO power converters,
Reference numerals 114, 115, 119 and 120 denote cycloconverters, and 121 to 130 denote AC electric motors. This rolling control system is a system for rolling a material that is still red hot and is called a hot rolling control system. It is a rough rolling system (stands R1, R2, R3 for rolling a thick material under high pressure. ) And finishing rolling system (stands F1, F2, F3, F4,
F5, F6, F7).

The configuration of the cycloconverter is shown in FIG.
FIG. 4 shows the configuration of the GTO power converter, and the features of each will be described. In FIG. 3, the device configuration of the cycloconverter includes a transformer 301 and a cycloconverter 30.
2, switch 303, AC motor IM304,
The cycloconverter has the following features. Feature (1): Output torque waveform has few ripples. Therefore, highly accurate tension control is possible. Feature (2): Limited by commutation angle of thyristor,
The control range of the output frequency is limited to only 1/2 to 1/3 of the power supply frequency. In addition, since many thyristor elements are used, the number of transformers 301 for supplying electric power increases, which requires an enormous amount of space and wiring, resulting in large power loss during operation. In addition, since the operating power factor is poor, the reactive power is large, 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 existing equipment. . Equipment that does not have enough power needs SVC in order to improve the power supply power factor. On the other hand, the SVC has a problem that the power loss at the time of no load is large. In FIG. 4, the GTO power converter is a system in which alternating-current power is converted into direct-current power by a converter and then converted into alternating-current by an inverter.
1, GTO converter / inverter 402, switch 4
03, AC motor IM404. The GTO converter / inverter has the following features. Feature (1): GTO can generate a higher frequency than a cycloconverter, and since the power factor of the converter on the power supply side can be controlled to 1, it is sufficient if there is enough power for the capacity of the equipment. It has the advantage of being easy to add to existing equipment. The number of transformers that supply electric power is also small, and the space for power supply equipment is very small compared to a cycloconverter.
Further, since the GTO converter can arbitrarily control the phase of the voltage and the current on the converter side, it is also possible to control the phase by the power factor of the power source and control the power factor of the power source. Overall efficiency is good because no SVC equipment is required. Feature (2): The torque ripple is larger in the motor output than the cycloconverter.

By the way, in FIG. 1, the stands R1, R2 and R3 of the rough rolling system are required to have a rolling power performance in view of the plate thickness accuracy of the product, and perform an extremely overload operation. This causes a reactive current. So GTO
Due to the features of the converter / inverter, the GTO that can control the power factor of the power supply can be used as a stand R for the rough rolling system.
1, R2, R3 to suppress the generation of reactive current.
On the other hand, the finish rolling system stands F1, F2, F
3, F4, F5, F6, and F7 determine the accuracy of the final product, and high precision rolling with less disturbance is required. A characteristic of rolling is that the product undergoes work hardening while being rolled by each stand, making it 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 in the front stage of the finish rolling system. Middle stand F
In Nos. 3, F4, and F5, the torque disturbance is absorbed by the tension control of the rolling mill, so that the material is less affected. Therefore, GTO with a high power factor is applied here. Since the quality of the product is decided by the stands F6 and F7 in the final stage,
Use a cycloconverter with less disturbance. This makes it possible to manufacture highly accurate products. However, when the cycloconverter is applied, reactive power is generated, and there is a demerit that the voltage fluctuation and the power supply capacity must be increased, and a special device (SVC) for compensating for this is required. However, in this rolling control system, by applying GTO at the same time, the power factor of the power source on the power receiving side is monitored to control the power factor of the GTO converter, and the reactive power generated from the cycloconverter is controlled by a special reactive power. Improves power factor without using a power compensator.
The principle of improving the power factor will be described with reference to FIG. In Figure 2,
Stands F1 and F2 in the front stage of the finish rolling system shown in FIG.
And the state of generation of reactive power by the cycloconverter of the last stage stand 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. The state which compensates a reactive power is shown.

In this embodiment, the GTO converter / inverter of the rough rolling system and the GTO converter / inverter of the finish rolling system are used, and the power source power factor at the power receiving point (point A in FIG. 1) is The power factor of each GTO converter is controlled to reach the target value. The details will be described below. The power of the front stage F1, F2 and the final stage F6, F7 of the finish rolling system is F ₁ , F ₂ , F ₆ , F ₇ KV, respectively.
A, the power factors are COSθ ₁ , COSθ ₂ and COS, respectively.
Assuming θ ₃ and COS θ ₄ , the total amount of reactive power A ₁ of the cycloconverter is R ₁ , R ₂ , the capacity of the converter of each GTO,
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
It becomes SIN θ ₄ . The power corresponding to the total amount A ₁ of this reactive power is GTO
The power factor is controlled to generate an electric power of −A ₁ and the power factor is controlled to _{1 in 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 phases of the current and voltage of the GTO converter are 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 COSθ ₁ + F ₂ COSθ ₂ + F ₆ COSθ ₃ + F ₇ on the cycloconverter side.
COSθ _{4 On the} GTO side B ₂ = R ₁ COSα ₁ + R ₂ COSα ₂ + R ₃ COSα ₃ + F ₃
COSα ₄ + F ₄ COSα ₅ + F ₅ COSα ₆ becomes B ₁ + B _{2 in} total. In this way, the power supply power factor can be set to 1 by the phase control of the GTO converter, so the KVA required for the power supply is B
It can have the same value as ₁ + B ₂ , which allows the power supply to be minimized. Therefore, even in an office where the power source is weak, it is possible to realize the maximum rolling control system with the minimum capacity and the minimum equipment. Note that in FIG. 1, the GTO
The converters of the converter / inverter are independent for each stand, but it is the same even if they are integrated as a common converter. Further, in the present invention, the same function is exhibited by applying the pulse width modulation converter / inverter even if other power source equipment having a poor power factor is adopted in addition to the cycloconverter.

[0010]

As described above, according to the present invention,
A special reactive power compensator by combining a cycloconverter and a GTO power converter in the electric motor drive system of the rolling mill, combining the characteristics of each feature, and adapting to the control characteristics of the rolling mill. It is possible to realize high-efficiency and high power factor rolling control without requiring. In addition, by using the cycloconverter and GTO power converter together, the power supply power factor can be controlled to 1. Therefore, it is sufficient if there is enough power for the capacity of the equipment. It also has the advantage of being easy, and because the number of transformers that supply power is small, the space for power supply equipment can be made very small. Furthermore, GT
Since the power converter of O can arbitrarily control the phases of voltage and current, it is possible to control this phase according to the power factor of the power source and control the power factor of the power source, and the reactive power compensator is unnecessary. Therefore, the efficiency is improved overall. Further, since the cycloconverter has a small ripple in the output torque waveform of the electric motor, it is possible to perform tension control with high accuracy in the rolling system.

[Brief description of drawings]

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

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

[Figure 3] Cycloconverter equipment configuration

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

FIG. 5: Example of rolling control system

FIG. 6 Rolling control system to which a conventional cyclo-converter is applied

FIG. 7: 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 transformer 111,112,116,117,118 GTO electric power converter 114,115,119,120 Cycloconverter 121-130 AC electric motor R1, R2, R3 Rough rolling system stand F1, F2, F3, F4, F5, F6, F7 Stands for finish rolling system

Claims (4)

[Claims] 1. A rolling plant having a plurality of AC motors and a power converter driving the AC motors, wherein the rolling plant serves as the power converter to convert a DC voltage into AC power and control a power source power factor. A pulse width modulation converter / inverter (hereinafter referred to as PWM),
A rolling control system, wherein a cycloconverter or a power supply facility having a low power factor is applied at the same time to absorb reactive power of the cycloconverter or the power supply facility. 2. In a rolling plant having a plurality of AC electric motors and a power converter driving the AC electric motors, a cycloconverter or a power supply equipment having a poor power factor is applied to rolling equipment requiring a high degree of torque control, and at the same time other A rolling control system characterized by applying a PWM for controlling a power source power factor to the rolling equipment of. 3. The rolling plant according to claim 1 or 2, wherein the rolling plant has a rough rolling facility and a finish rolling facility, at least one PWM is applied to the rough rolling facility, and one of the finish rolling facilities is used. One or more cycloconverters are simultaneously applied to improve the power source power factor by the PWM phase control, and at the same time, the cycloconverter performs operation with less torque ripple in the output of the electric motor. 4. The rolling plant according to claim 1 or 2, wherein the rolling plant has rough rolling equipment and finish rolling equipment, PWM is applied to the rough rolling equipment and the finish rolling equipment, and A rolling control system characterized in that a cycloconverter is applied to the front stage and the final stage, the power source power factor is improved by the phase control of the PWM, and the cycloconverter performs operation with less torque ripple in the output of the electric motor.