Abstract: This paper introduces the successful application of AC and DC drive devices in the medium plate roughing rolling reduction system. These two applications respectively used AB AC frequency converters and Siemens DC digital devices as the core to construct their respective network control systems. The paper compares and analyzes the application effects, technical challenges, and parameter optimization of the two methods.
Keywords: AC frequency converter; DC digital device; performance comparison;
The Application and Compare Analyse of The Control System of AC & DC in the System of Depressive on the Thick Rolling Mill
(The Medium Plate Plant of Jinan Iron and Steel Co., Ltd., Jinan 250101, China, Chen Jinbiao, Zhou Tao, Duan Wenyu, Li Wei, Li Desong)
Abstract: This article introduced the successful application of the AC & DC drive device on the depress system of the thick rolling mill in the middle plate factory. The twice application trussed the net structure according to the AC transducer of the AB and DC numeric device of the SIEMENS as the core. The article compared and analyzed the effects of the application and the difficulties of the technology and the optimize of the parameter.
Keywords: ; AC TRANSDUCER ; DC NUMERIC DEVICE ; THE COMPARE OF CAPABILITY ;
1. Introduction
In the current control field, vector frequency conversion technology is mature and widely used. In the roughing mill reduction control system project, AB's vector frequency conversion technology was first applied. The mill reduction motor used an AC motor, and the cooling system was a water-cooled air-cooled system. Many technical problems and difficulties arose during application. Through continuous learning, practice, and exploration, a series of technical application problems were finally completely solved, including slow starting speed of the reduction motor, unstable operation, unbalanced operating loads on both the operation and transmission sides, and burnout of the operating side motor. However, in subsequent production practice, we found that long-term operation under the requirements of frequent forward and reverse rotation, high torque, high temperature environment, and rapid response in roughing mill reduction places very high demands on the motor itself, and there are still very significant potential risks and hidden dangers.
Therefore, after a year of applying AB vector frequency conversion technology, we replaced the AC system with a DC system based on Siemens DC digital devices. DC speed control technology is already very mature, with excellent static and dynamic performance. Through the application of SIMOLINK master-slave control, the advantages of the DC system were realized. This met the requirements of the production process and enabled the DC motor to operate stably for a long time in the roughing rolling process. This made the roughing rolling system a truly "maintenance-free" system, greatly reducing maintenance costs and saving manpower. Below, we will discuss the application comparison and technical issues of AC and DC systems in the roughing rolling process.
2. Hardware Components and Their Comparison
2.1 Introduction to the similarities and differences in the hardware of the AC/DC system for roughing rolling mill reduction
2.1.1 Similarities:
All components consist of a Siemens S7 400 PLC, an ET200 substation, a host computer, two YP235L-8 200KW 518rpm AC variable frequency motors, an MTS displacement sensor, a DC220V DC device, and its clutch system.
2.1.2 Different parts:
(1) The drive system uses AB vector frequency converter and SIEMENS DC 6RA70 digital device respectively;
(2) In motor cooling, AC motors use a water-cooled air-cooled system, while DC motors use a forced low-temperature air-cooled fan.
(3) There are no reactors in the AC system, but the DC system adds incoming and outgoing line reactors;
2.2 Master-Slave Control Board of Vector Frequency Converter
(1) Wiring instructions for the terminals of the operating (active) side inverter
TB10 and TB11 terminal block specifications:
(2) Wiring instructions for the drive (driven) side inverter terminals
Instructions for TB10 and TB11 drive terminals:
The above terminal design lays the hardware foundation for master-slave control of the motor on both the operating and drive sides in an AC frequency converter system, and also provides a basis for setting the frequency converter parameters.
2.3 Composition of the master-slave control network on the operating side and drive side of the DC-DC pressurized motor system
(1) Hardware configuration diagram of master-slave control network:
(2) Siemens Master-Slave Control Hardware Description
To achieve high-precision synchronization, this design utilizes Siemens' all-digital device component SLB board, with one board on the operating side and one on the drive side to complete the communication task for master-slave control. The two SLB boards are connected by a dedicated optical fiber.
The SLB board transmitting port of the operating side device is connected to the receiving port of the SLB communication board on the transmission side via optical fiber, and the SLB board receiving port of the operating side device is connected to the transmitting port of the SLB communication board on the transmission side via optical fiber. After the actual connection is normal, the communication light of the SLB board turns green and flashes.
2.4 Comparison of the hardware composition and functions of AC/DC systems
The functionality of AB vector frequency converter technology is ultimately achieved through point-to-point hardware connections between the ET200 in the control room and the frequency converter, as well as parameter settings within the AB vector frequency converter. However, in a system centered on a Siemens DC digital device, all functions related to the digital device and master-slave control are accomplished through a DP network and fiber optic communication. Therefore, from a hardware perspective, the DC speed control system is superior to the AC vector frequency converter system, and is more conducive to achieving functions such as system control accuracy, system synchronization, and load balancing.
3. Introduction to System Network Configuration and Comparative Analysis
3.1 The AC/DC frequency converter network configuration architecture for roughing mills is as follows:
Network configuration instructions:
Among them, UR1, UR2, and stations 3 and 4 are the original configurations of the roughing mill auxiliary drive system, which complete the control tasks of front and rear roller conveyors, east and west stand roller conveyors, rear conveyor roller conveyors, and east and west pushers.
The red line in the overall configuration diagram represents the newly added network configuration when converting from AC to DC pressure reduction system. Stations 10 and 11 are ET200 substations, and stations 12 and 13 are DC pressure reduction Siemens all-digital devices. All four substations are connected to the original and auxiliary drive network, which saves hardware resources and facilitates the sharing and utilization of information between the original and auxiliary drive system and the existing pressure reduction system.
A master-slave control configuration is completed by connecting stations 12 and 13 via a fiber optic link.
3.2 Network Architecture Comparison and Analysis:
(1) In the AC voltage reduction system network, station 6 in the AB vector inverter cabinet in the control room is a substation of the system. It completes the various control functions of the inverter TB3, TB10 and TB11 terminals through hard wire connection.
(2) In the DC pressing system, the control of the device is completed through DP network communication;
(3) The difference in configuration between the two directly affects the difference in the speed and timeliness of the control task response. In maintenance, this is directly reflected in the fact that the maintenance workload and failure rate of the AC system are much higher than those of the DC system.
(4) The network communication method of the DC pressing system lays the hardware foundation for the rich development of the host computer and directly provides important historical analog data for the daily maintenance of the pressing system;
4. System design features and comparisons:
4.1 Technical Challenges and Solutions in the Application of Vector Frequency Conversion Technology in Rough Rolling
4.1.1 Existing Problems
(1) When pressing down to start the motor, if the input is too small, the response is slow, the motor makes a humming sound but is difficult to start and rotates back and forth;
(2) When the large setpoint starts, the inertia is very large and difficult to control, which makes it impossible for the operator to reach the expected roll gap value. Multiple adjustments are required to reach the target roll gap value, which seriously affects the production rhythm.
(3) The operating side motor and the transmission side motor are very different, and there have been multiple accidents of burning out the transmission side motor.
4.1.2 Solution
Based on the analysis of the phenomena in the above problem summary, we set parameter P184=19 in the parameters to indicate that when terminal 27 of TB3 on the 1336-L9 control board is at a high potential, the vector control system will enable the FLUX UP function. The use of this function will add a sustaining starting current to the motor and speed up the starting speed. Using a HIOKI8841 multi-channel oscilloscope, we monitored the waveforms of the motor current values at terminals 18 and 19 of TB10 on the drive side and the operating side of the inverter. We found that the magnitude of the motor current on both sides was very different, the amplitude was different, and the waveform was also different. We corrected the bias coefficient of the setpoint from the operating side inverter by using the AN IN 2 SCAL parameter on the drive side.
4.1.3. Improved application effects
(1) The purpose of using the Fast flux up function is to provide a holding current when the master command returns to zero and restarts within 10 seconds, thereby increasing the starting torque and achieving a fast start-up effect.
(2) Moreover, since the current limit is reduced, the rotational inertia is also reduced, so it can stop accurately at the target roll gap value.
(3) After the setpoint coefficient of the drive-side inverter was corrected from 2 to 3.5, the current waveforms on both sides became consistent, the temperature difference of the motor began to shrink, and finally became almost identical.
4.2 Technical Application Characteristics of the 6RA70 DC Unit for Rough Rolling Reduction
4.2.1 Characteristics of the host computer
This software design paid particular attention to the rational development of the host computer interface, striving to achieve comprehensive, scientific, timely, and continuous monitoring of the roughing mill reduction system. To this end, the following functions were added to the original host computer interface of the roughing mill auxiliary drive system: comparison curves of changes in current, armature voltage, excitation voltage, excitation current, and six temperature measuring points of the motor; roll gap trend interfaces on the operating side and drive side; and rolling force change trend graphs on the operating side and drive side.
This interface collects data on roll gap changes and rolling force throughout the rolling process, providing direct analytical data for optimizing the rolling process. It also provides electrical maintenance personnel with another important data analysis tool in the event of an accident.
4.2.2 This design reasonably incorporates a DP network to collect rolling force and adds an interlocking signal to the program. Whenever the rolling force exceeds 1200 tons, the DC fully digital rolling mill system is locked down. Technically, this completely eliminates the potential threat of misoperation to the rolling mill motor, ensuring long-term stable operation of the roughing mill rolling mill motor under high load and high current conditions.
4.2.3 This design also considers the option to operate in single-motor mode after an unexpected motor failure. If a problem with the motor itself prevents the motor from operating in a coordinated manner, the operator can switch to single-motor mode by cutting off the enable signal of the 6RA70 digital DC power supply to continue production without causing a prolonged shutdown.
4.2.4 Reasonable modification of the cooling system: The cooling method of the small motor on the top of the rolling mill was changed to a forced air cooling method of the 25kw motor on the ground through cooling pipes, which greatly improved the cooling method of the motor. The air intake of the ground cooling fan comes from the cold air cooled by the air conditioner in the control room. This ensures that the motor is kept at a low temperature for heat dissipation even in summer.
5. Application Effect Description
5.1 Application Effects of the Improved Vector System
(1) The output current waveforms of the motor on the operating side and the drive side changed from being quite different to being almost the same.
The waveform comparison diagram between the operating side and the transmission side is shown below:
Current waveforms on the operating side and drive side before parameter optimization:
Based on the oscilloscope waveform data from the dual-channel test, the maximum value of the motor current under operating pressure (yellow) is about 311A higher than that under transmission pressure (green). Under such operating current, long-term production will naturally result in a significant difference in the motor's body temperature.
Current waveforms on the operating side and drive side after parameter optimization:
Based on the oscilloscope waveform data from the dual-channel tests above, the motor current under operating side pressure (yellow) is almost equal to the motor current under drive side pressure (green). This indicates good follow-through and a well-balanced load.
(2) During the 10-hour operation, the temperature of the variable frequency motor on the operating side gradually decreased from about 70 degrees to about 36 degrees, which is almost the same as the 35 degrees on the transmission side.
The overall effect is that operators can quickly start the pressing motor and accurately stop at the target roll gap value. The time required to roll a piece of steel using rough rolling mill has been reduced from 76 seconds to 54 seconds, significantly accelerating the production pace. This has played a crucial role in the rapid achievement of production targets and efficiency in our factory's "three-to-four" project.
5.2 Application Effect of DC System
The core of this system design is the successful application of Siemens SIMOLINK communication, which realizes the synchronization of master-slave control of the motors on the operating side and the drive side, and achieves excellent load balancing effect.
5.2.1 The use of SIMOLINK fiber optic communication fully realizes the synchronization of control between the operating side and the drive side, laying a solid foundation for the long-term stable operation of the motor. Through multi-trace oscilloscope testing, the current synchronization control error between the operating side and the drive side is within 90ms, greatly improving control accuracy.
5.2.2 The motor cooling system is excellent. The operating side and drive side motors maintain a good operating temperature of below 70 degrees Celsius when the ambient temperature is 40 degrees Celsius in summer, thus providing favorable external temperature protection for the long-term safe operation of the motor.
5.2.3 The system design ultimately achieved synchronization of master-slave control, rapid motor start-up, and accurate positioning. According to statistics, after the project was applied, the time for each steel billet to be opened could be shortened by about 2 seconds, and the production per shift could be increased by about 160 tons. This alone can generate more than five million yuan in additional benefits annually.
6. Conclusion
The successful application of both technologies in the roughing mill reduction system has: The former has instilled confidence in the AC conversion of large DC motors and accumulated valuable practical experience for further promoting vector frequency conversion technology in industrial production. This technology reduces the amount of maintenance required for the motor itself, lowers maintenance labor intensity, and ensures long-term stable system operation while effectively addressing motor heat dissipation issues; the latter, through the successful application of Siemens SIMOLINK fiber optic communication technology in the roughing mill reduction motor control system, ensures the synchronization of the motors on both the operation and transmission sides, achieving load balancing. The modification of the motor cooling system, the rational development of the host computer, and the scientific application of interlocking signals ultimately enabled the long-term stable operation of the roughing mill DC reduction system and the fault-free operation of the motors.
Overall, both can meet the requirements and parameters of the production process. However, the requirements for the quality of the motor body and the cooling method and its effect to ensure the long-term stable operation of the two systems are different. The requirements of the vector frequency conversion system are significantly higher than those of the DC system architecture. Therefore, we recommend that a DC motor be used for driving in the rough rolling pressing stage.
About the Author
Chen Jinbiao, male, 30 years old, native of Sichuan, is an electrical engineer. He graduated from the Department of Mechanical and Electrical Engineering of Xinjiang Petroleum Institute in July 2002 with a Bachelor of Engineering degree. He currently works primarily in the technical management and maintenance of electrical control systems, and the application of new technologies.
Contact number: 0531-88865679; Postcode: 250101; E-mail: [email protected]
