Abstract: This paper introduces the causes and solutions to the technical problems of high motor temperature, motor burnout, and load imbalance on both the drive and operation sides when using Siemens DP network, AB vector frequency converter, and other technologies in the AC reduction control system of the medium plate roughing mill. Keywords: vector frequency converter; load balance; motor burnout 1. Introduction The roughing mill reduction control system is a sub - project of the roughing mill auxiliary drive system in the "three-to-four" system project of the medium plate mill, and it is also a very important part of the roughing mill system project. Currently, in the national steel rolling industry, the vast majority of rolling mill reduction motors use DC speed control systems. The advantage is that DC speed control technology is very mature and offers excellent static and dynamic performance. The disadvantage is that due to the structural characteristics of DC motors, such as brush holders, carbon brushes, and commutators, the motors face significant maintenance difficulties and increased costs under harsh operating environments like vibration, dust, and high temperatures at the top of the rolling mill. In the current control field, vector frequency conversion technology is mature and has been widely and successfully applied. This project successfully introduced AB's vector frequency conversion technology, using a 200kW AC motor from Jiamusi for the rolling mill reduction motor. The cooling system is a water-cooled air-cooled system. In the early stages of applying the vector frequency conversion reduction speed control system, many technical problems and difficulties arose. These included a long-term inconsistency between the motor temperature on the transmission side and the operating side, resulting in a high temperature and a major equipment accident where the operating side motor burned out. After continuous learning and extensive research of vector frequency conversion technology by technical personnel, and through a period of technical breakthroughs, a series of technical application problems were finally and completely solved, including slow starting speed and unstable operation of the pressing motor, unbalanced operating and transmission loads, and burnout of the operating side motor. This achieved long-term stable operation of the AC motor in roughing rolling pressing, making the roughing rolling pressing system a truly "maintenance-free" system, greatly reducing maintenance costs and saving human resources. 2. Introduction to the Application of Vector Frequency Conversion Technology in Roughing Rolling Pressing This control system is a vector control speed regulation system composed of a Siemens PLC S7 400, ET200 substation, host computer, AB vector frequency converter, two YP235L-8 200KW 518rpm AC frequency conversion motors, and American MTS absolute displacement sensors. The PLC mainly controls the vector inverter, receives the analog signal collected by the ET200 substation of the control panel #3 and outputs it to the AB vector inverter as the given signal through the analog output module of the substation in the control room, and completes the relay control of inverter opening, closing, enabling, single action, linkage, manual and automatic. The host computer is mainly responsible for communicating with the PLC, implementing real-time monitoring and online program modification. After receiving the given signal, the AB vector inverter determines the speed and direction of the variable frequency speed drive motor according to the magnitude and sign of the analog signal. 2.1 When the rough rolling pressing vector control speed regulation system is working, the operator can select the three operating modes of single action on the operating side, single action on the transmission side and linkage through the operator panel switch. (1) When the “linkage” mode is selected, the master and slave synchronous operation can be realized. In this mode, the operating side is active operation, that is, speed mode operation. The transmission side is slave operation mode, that is, torque operation mode. To achieve synchronous operation of the operating side pressure motor and the transmission side pressure motor, the clutch is de-energized, and the operating side motor and the transmission side motor are coaxially connected. (2) When the "operating side single-action" mode is selected, the clutch is energized, and the operating side motor is actively running, i.e., speed mode operation. At this time, the transmission side frequency converter system is blocked, and the transmission side motor does not operate. (3) When the "transmission side single-action" mode is selected, the clutch is energized, and the transmission side motor is actively running, i.e., speed mode operation. At this time, the operating side frequency converter system is blocked, and the operating side motor does not operate. In this way, the two "operating side and transmission side single-action" operation modes can realize the individual adjustment of the operating side screw and the transmission side screw, quickly compensate for the deviation of the operating side and transmission side roll gap value caused by the wear clearance of mechanical equipment during the rolling process, thereby meeting the requirements of the rolling process for roll gap value adjustment. 2.2 Principle and parameter optimization of the vector inverter According to the design requirements, we designed the wiring instructions for the control board terminals of the 1336 IMPAC inverter as follows: (1) Wiring instructions for the inverter terminals on the operating side: TB10, TB11 terminal instructions: TB3 terminal instructions: (2) Wiring instructions for the inverter terminals on the drive side: Drive TB10, TB11 terminal instructions: Drive TB3 terminal instructions: The above terminal design lays the hardware foundation for realizing the master-slave control of the motor on the operating side and drive side, and also provides a basis for setting the inverter parameters. 3. Specific difficulties and technical challenges in the application process 3.1 Technical difficulties and solutions in the application of vector frequency conversion technology in roughing mill 3.1.1 Problems exposed in the initial stage of motor load commissioning of the vector frequency conversion system in roughing mill: 3.1.1.1 Summary of problems: (1) When the motor starts, if the setpoint 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 starting with a large setpoint, the inertia is very large and it is not easy to control, which makes it impossible for the operator to reach the expected roll gap value. It is necessary to make repeated adjustments to reach the target roll gap value, which seriously affects the production rhythm. 3.1.1.2. Solution Based on the analysis of phenomena (1) and (2) in the above problem summary, we consulted the 1336IMPAC manual and found that in order to make it easier to start, the vector frequency converter has a magnetic flux preset function, namely the FLUX UP function. (1) Setting parameter P184=19 in the parameters indicates 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. (2) Change the "8" bit of parameter P013 from "0" to "1" to enable the "fast flux up" function. (3) Write a program for terminal 27 of TB3 in the FB30 pressing program package to maintain terminal 27 at a high level for 10 seconds when the pressing analog signal master is at zero position, and enable the "fast flux up" function. During these 10 seconds, there is a sustaining current of about 120A inside the variable frequency motor. (4) The current limit value has been reduced from 220% to 180%. 3.1.1.3. Improved application effect (1) The purpose of using the Fast flux up function is to maintain the current when restarting within 10 seconds after the master command returns to zero, thereby increasing the starting torque and achieving a fast start-up effect. After this function is put into use, the problems (1) and (2) in the "Problem Summary" are immediately solved, and the operators report that the starting speed is faster. (2) Due to the reduction of the current limit, the rotational inertia is also smaller. The overall effect is that the operator can both start the pressing motor quickly and stop accurately at the target roll gap value. 3.1.2 Problems exposed in the early stage of production under load of the roughing mill vector frequency conversion system: 3.1.2.1 Problem summary: (1) The temperature of the pressing motor on the operating side is always about 15 to 35 degrees higher than that of the pressing motor on the transmission side. That is, when the temperature of the pressing motor on the transmission side is about 35 degrees, the temperature of the motor on the operating side is about 60 degrees, and can reach up to 70 degrees. (2) The power terminal of the motor body on the operating side is overheated and has a second mark. Temporary treatment is carried out. (3) One motor on the operating side is burned out and the motor winding is damaged. 3.1.2.2. Problem Analysis Based on the analysis of phenomena (1), (2), and (3) in the problem summary, it can be determined that the load on the operating side is always greater than that on the transmission side motor in actual production. We analyze the reasons as follows: (1) The production process is a linkage operation mode, that is, the operating side is the active, speed operation mode, and the transmission side is the driven, torque operation mode. The torque given in the driven, torque operation mode of the transmission side comes from the analog signal of terminals 15 and 16 in TB10 on the operating side, which is connected through the hardware control line. Then, the same given value is transmitted to the operating side and then transmitted to the transmission side through the hardware line. Therefore, the given value of the transmission side will definitely lag. At the same time, the given signal of the operating side and the given value of the transmission side will definitely be inconsistent. The transmission lags behind the operating side system, which is called a load on the operating side. (2) The vector inverter control uses the FLUX UP function of the AB company's IMPAC inverter, which makes 120A current still in the motor after the master command returns to zero, which will increase the heat generation of the motor. 3.1.2.3. Problem solution (1) Use HIOKI8841 multi-channel oscilloscope to monitor the waveform of the motor current value at terminals 18 and 19 of the TB10 terminal of the drive side and the operating side inverter. It was found that the motor current was very different, the amplitude was different, and the waveform was also different. (2) Adjust the AN IN 2 SCAL parameter of the drive side to correct the bias coefficient of the data setpoint from the operating side inverter. Start from 2 and increase to 2.5, 2.8, 3, etc. Observe that the waveform begins to change and the operation effect of the drive side tracking the operating side is improved, but it is still inconsistent. (3) Continue to adjust. After the AN IN 2 SCAL coefficient is increased from 3 to 3.456, the drive side follows the change of the operating side current very well. 3.1.2.4. Improved Application Effect (1) The output current waveforms of the operating side and the drive side motors changed from being significantly different to being almost equal. The waveform comparison diagram of the operating side and the drive side is as follows: Current waveforms of the operating side and the drive side before parameter optimization: From the above oscilloscope dual-channel test waveform data, the maximum value of the motor current (yellow) under the operating side pressure is about 311A ​​higher than that of the motor current (green) under the drive side pressure. Under such operating current for long-term production, the temperature of the motor body will naturally be very different. Current waveforms of the operating side and the drive side after parameter optimization: From the above oscilloscope dual-channel test waveform data, the motor current (yellow) under the operating side pressure is almost equal to that under the drive side pressure. The following is very good, and a good load balance effect is achieved. (2) During the 10-hour operation, the temperature of the operating side variable frequency motor gradually decreased from about 70 degrees to about 36 degrees, which is almost the same as the 35 degrees of the drive side. The overall effect is that operators can quickly start the rolling mill motor and accurately stop it at the target roll gap value. The time required to roll a piece of steel in the roughing mill has been reduced from 76 seconds before the improvement to 54 seconds after the improvement, significantly accelerating the production pace. This played a crucial role in the rapid achievement of production targets and efficiency in our plant's "Three-to-Four" project. 4. Economic Benefit Analysis and Conclusion The successful application of vector frequency conversion technology in the roughing mill rolling system and the AC conversion process of large DC motors have instilled confidence and accumulated valuable practical experience in technical applications, setting an application example for further promoting the application of vector frequency conversion technology in industrial production. The application of this technology has enabled the long-term safe and stable operation of the roughing mill rolling motor system, improved production pace, saved spare parts costs, reduced the amount of maintenance required for the motor itself, and lowered the intensity of maintenance labor, creating significant economic benefits for the head office.