Abstract : This paper introduces the auxiliary drive system of the leveling mill in the cold rolling production line and the control methods and parameter settings of the 6SE70 inverter. Multiple networks are used to achieve high-precision control and safe operation of the drive system. Keywords : 6SE70 inverter; auxiliary drive; common DC bus; network 1 Introduction The Jinan Iron and Steel Group's cold rolling production line boasts a high level of technology in both process equipment and automation control systems. The leveling mill is one of the important pieces of equipment in the cold rolling production line. Its auxiliary drive system mainly consists of the XPact ProBas process control system, the Siemens PLC control system, the common DC bus frequency conversion speed regulation system, and the safety PLC system. The system adopts multiple communication buses such as VME, Profibus-DP, and SafetyBUS to achieve the high-performance drive requirements of the auxiliary drive system. The main drive equipment of the leveling mill auxiliary drive system includes: coil lifting device, preparation station drum, exit guide roller, roll changing clamp, roll changing trolley, and coil transport trolley. 2. Auxiliary Drive Control System The leveling mill auxiliary drive control system adopts the XPact ProBas mill automation control system developed by SMS Demag. This system is a powerful automation system developed to meet the stringent requirements of the dynamic performance of servo hydraulic and process control systems. It uses advanced PC multiprocessor technology, with application software developed in a graphical mode on a Windows PC. The frequency converter receives speed reference values ​​from the XPact ProBas system, obeys the control and fault handling of the XPact ProBas system, and simultaneously transmits the actual speed value and related equipment status to the XPact ProBas system for processing. The input/output signals of the remote I/O (ET200 station) mainly include equipment status and operation signals, and participate in the equipment's logic control. Auxiliary drive devices closely related to the speed of the leveling mill main drive system, such as guide rollers, have speed sensors with dual outputs, one of which is sent to the 6SE70 frequency converter to achieve closed-loop speed control. Another path is directly connected via a hardwired connection to the counter module of the leveling mill's VME system. After data processing, the actual rotational speed of the drive unit is obtained and used as a feedback signal for the speed controller, participating in the calculation of the speed reference value, thereby achieving high-precision speed control. The leveling mill X Pact ProBas system mainly includes: a main controller (MAC), speed control (SCM), tension control (ITEN), hydraulic roll gap control (HGC), sheet shape control (FCS), mill drive control (MDC), and guide roll drive control (DRD), among other process control systems. Among them, the DRD, CCAR, and RCC process control systems realize the logic and closed-loop control of auxiliary drive equipment such as guide rolls, coil transport cars, and roll changing cars. The speed controller (SCM) provides speed setpoints for all drive motors based on the operating conditions of the leveling mill system and the drive conditions. The reference value set by the secondary system and the master command serve as the speed setpoint input, first sent to the exit mill, and then the speed setpoint for each drive unit is calculated based on the speed factor. Based on the actual rotational speed, the acceleration torque and friction torque of the drive are calculated, and it is determined whether open-loop torque control is required. Acceleration torque and actual speed are calculated using SCM to obtain reference values ​​for the drive speed. Speed ​​control of the drive equipment is achieved through Profibus DP network communication. 3. Common DC Bus Variable Frequency Speed ​​Control System The system adopts Siemens' common DC bus variable frequency speed control system. The main circuit scheme of the auxiliary drive system is shown in Figure 1. The rectifier, inverter, and braking unit all use the 6SE70 series device, which has the following characteristics: it has a vector control regulator with an output frequency range of 0-300 Hz, and the speed control accuracy with encoder can reach 0.1% (response time with mechanical load is 120ms). It can realize multiple control modes such as torque and speed, and has software self-testing and hardware self-testing functions, as well as strong comprehensive detection and diagnostic functions. In this system, fuse disconnect switches are installed between the DC bus and the inverter drive device to protect the inverter. All drives related to cold-rolled strip use pulse encoders to achieve closed-loop speed control, and a dv/dt filter is installed on the AC output side to reduce interference to other systems. [align=center]Figure 1 Main Circuit Scheme of Auxiliary Drive System[/align] Practice has proven that the drive control system using a common DC bus has many advantages: ⑴ Excellent dynamic performance. The auxiliary drive system of the leveling machine requires excellent dynamic performance and high control precision. Using DC bus technology achieves balanced energy distribution and effectively suppresses overcurrent and overvoltage faults during dynamic speed regulation. ⑵ Reduced equipment investment and failure points. The rectifier section and additional braking resistors of each inverter are eliminated, reducing the number of devices and achieving standard inverter configuration, thus improving motor characteristics. ⑶ Significant energy savings. During leveling machine production, the auxiliary drive equipment operates in different states. Inverters in braking state convert mechanical energy into electrical energy and feed it back to the DC bus to power other inverters driving motors, thus significantly reducing overall energy consumption. 4 Inverter Parameter Setting and Optimization Depending on the type of drive equipment, different control methods are used for the inverter. The No. 1, No. 2, and No. 3 coil transport cars, lifting devices, elevator traverse devices, roll changer clamps, No. 1 and No. 2 roll changer cars, and roll changer traverse devices all use V/F control, while the preparation station drum, the 3-roll straightening machine, and the exit guide rollers use speed vector control. The basic process for setting the inverter parameters is as follows: After powering on the inverter, first restore the parameters to factory settings, then configure the CBP board, selecting P060=5 for system settings, and finally configure the control word and status word connections, connecting the vector control switch quantity and vector control connection quantity to the parameter values ​​and control words defined in X-pact ProBas. The main connection parameters of the system are shown in Table 1. Table 1: Main Connection Parameters for Inverter Communication [align=center] [/align] To accurately determine motor parameters and improve dynamic performance, each control inverter performs automatic motor identification and speed regulator optimization. Automatic identification and regulator optimization can be achieved using "System Settings". Using P151=2, the stationary motor is identified; P151=4, the motor model is calculated for no-load measurement; P151=5, the motor model is calculated and the regulator is optimized. The speed regulator's gain Kp (P235, P236) and other parameters depend on the system's inertia and should be manually adjusted according to actual operating conditions. During debugging, some devices exhibited significant dynamic performance variations under different loads. Through multiple optimizations of the speed controller and current controller, and manual modification of relevant parameters, optimal settings were obtained, fully meeting the high-performance transmission requirements. Figure 2 shows the dynamic response curve of the guide roller recorded by the Drive monitor. [align=center] Figure 2: Dynamic Response Curve of Guide Roller[/align] 5 Safety PLC Emergency Stop System The safety PLC system consists of a local mainframe and remote I/O modules, connected via a secure network. The mainframe uses Pilz's PSS3100 series, composed of a power supply module, CPU, Ethernet module, and digital input/output modules. The safety PLC achieves high reliability and safety through special electronic circuitry, software, and redundancy measures. The safety PLC's communication system is SafetyBUS, an open network system that can connect many devices and is also a specially designed safety carrier. The safety PLC system automatically performs self-tests upon power-up, continuously performs self-tests during normal operation, executes a complete test within one hour, and simultaneously detects peripheral inputs and outputs. Peripheral detection includes: digital circuits of input modules, functional loss of output modules, output image workbench, feedback protection, etc. The auxiliary drive variable frequency speed control safety system has the following states: (1) Emergency Stop: After the system issues an emergency stop command, the equipment stops with maximum braking capacity. After stopping, the relevant control power supply to the area is cut off. In this case, strip breakage, entanglement, etc., are not considered; only the fastest stopping speed and equipment safety are required. (2) Rapid Stop: Rapid deceleration controlled by the process system until the equipment stops running. Rapid stopping should consider the coordination of production line stopping, ensure the safety of online products, and prevent strip breakage, entanglement, etc. (3) Equipment Adjustment: At this time, the system is in a linked state, and necessary adjustments can be made to certain equipment. (4) Individual Equipment Operation: Manual operation of individual equipment is performed through the control panel. (5) Equipment Inspection: This command is issued through the process system, at which point the operating speed is reduced to a minimum. 6. Electromagnetic Interference Issues in the Network System The leveling machine's automated control system uses various networks and buses, such as VME bus, Ethernet, Profibus-DP, and SafetyBUS. The drive system mostly uses frequency conversion drive, and some equipment has high power, making it crucial to prevent interference from the drive system to the network communication system. Therefore, the entire system is designed with a reliable grounding system, establishing a standard grounding reference potential (ground). All module racks and load current loops are connected to the common reference potential, ensuring that interference currents caused by improper cable laying or equipment installation are quickly diverted, thus preventing communication failures due to interference. Because the drive system requires significant power, power cables often transmit high voltage and high current. If such power cables are laid parallel to communication cables over long distances, capacitive and inductive interference will occur on the network cables, disrupting data communication in the network. To avoid this interference, during design and construction, the distance between communication cables and other wires and cables must be ensured, and power cables and communication cables should be laid separately on isolated cable trays as much as possible. 7 Conclusion After the cold rolling project was put into operation, the auxiliary drive system operated normally and reliably, fully meeting the process requirements of the cold rolling production line, laying the foundation for stable and high production, and achieving considerable economic and social benefits.