[b]1 Introduction[/b] Metal products are an important part of the metallurgical industry, but in my country, this industry is a weak link, with outdated machinery and electrical equipment hindering its development. In metal processing, straight-line wire drawing machines are common. Previously, DC generator-motor sets (FD systems) were typically used. Now, with advancements in technology and the widespread adoption of frequency converters, variable frequency control (VFD) is increasingly used in straight-line wire drawing machines. PLCs can be used to achieve functions such as setting drawing varieties, automating operation, controlling the production process, real-time closed-loop control, and automatic meter counting. Straight-line wire drawing machines using VFD speed control systems are technologically advanced and energy-efficient, with a speed range of 30:1 during normal operation, and providing more than 1.5 times the rated torque at 5% of the rated speed. This article uses the VFD retrofit of a straight-line wire drawing machine for stainless steel wire production in a factory as an example to illustrate the application process and effects of VFD control. [b]2 Variable Frequency Control System for Straight-Line Wire Drawing Machine[/b] This straight-line wire drawing machine is mainly used for drawing stainless steel wires produced by precision rolling. The design process requirements are: (1) Maximum wire drawing speed of 600m/min; (2) Three main types of wires are processed: 2.8mm infeed → 1.2mm outfeed, 2.5mm infeed → 1.0mm outfeed, and 2.0mm infeed → 0.8mm outfeed; (3) No more than two wire breaks during emergency stop. The straight-line wire drawing machine is the most difficult type of wire drawing machine to control because it uses multiple motors to stretch the metal wires simultaneously, resulting in high operating efficiency. Unlike the water tank wire drawing machine and looper wire drawing machine that were commonly encountered before, it does not allow the metal wires to slip between different dies. At the same time, it has high requirements for the synchronization of the motors and the speed of dynamic response. Due to the brittle nature of stainless steel, it lacks the toughness of high-carbon steel wire or steel cord and is relatively easy to break during operation. This system has a total of 8 11kW frequency converters. The electrical configuration of the system is shown in Figure 1. It includes one looper installed in the first stage, whose function is to draw the coiled stainless steel wire to the drawing section. Since the looper can slip freely, this motor does not require special control. The drawing section has six 400mm diameter drums. A cylinder swing arm is installed between each drum for position detection. A displacement sensor detects the position of the swing arm. When the wire is pulled taut, the wire exerts pressure on the cylinder of the swing arm, causing the swing arm to move downwards. Finally, there is the winding motor, which uses a self-sliding conical support. The coil diameter remains essentially unchanged throughout the process, so coil diameter calculation is not required. All eight motors are dedicated variable frequency motors and are equipped with mechanical braking devices. The system logic control of the straight-line wire drawing machine is relatively complex, with various linkage relationships, implemented by a PLC. Synchronization control is entirely implemented within the Huichuan MD320 frequency converter, without relying on external control. Its working principle is as follows: the operator sets the operating speed on the panel, and the analog signal of this speed enters the PLC. After considering the acceleration and deceleration time, the PLC outputs the analog signal with a certain slope. This is mainly to meet the needs of operations such as jogging and threading. The analog voltage signal output by the PLC is simultaneously connected to the AI2 (AI1 can also be used) input terminal of all frequency converters as the main speed setpoint signal. The signals from each swing arm displacement sensor are connected to the corresponding drum drive frequency converter as the feedback signal for PID control. A PID setpoint value is set according to the swing arm's position in the middle. This system is a very typical PID control system with feedforward, with each stage connected in series, and the PID output serving as a fine-tuning variable. The reason for choosing the Huichuan MD320 frequency converter is that it can easily achieve the function of main speed following PID fine-tuning without the need for an additional control board. The parameters in this system are set as follows: F0-03=2: Main frequency source X is AI2; F0-04=8: Auxiliary frequency source Y is PID. Since the stability of the system largely depends on the action of the PID, the tuning of its parameters must be carefully considered, taking into account low speed, high speed, acceleration, and deceleration. Additionally, differential limiting must be added to this system. [b]3 Conclusion[/b] After optimizing the parameter values, the system achieved a very stable speed of 600m/min during equipment testing, completely solving the problem of instability at high speeds when using synchronous board control (previously, it could only operate up to 300m/min). Through comparative tests under various operating conditions, this system performs the same as a wire drawing machine using an imported DC driver, while its equipment efficiency is 90-95% and its power saving rate is about 40%. Moreover, the electrical components of this system are simple and logically clear, and the cost is significantly reduced compared to the original system, making it a cost-effective solution. [b]References[/b] [1] MD320 Modular Frequency Converter User Manual [Z]. Shenzhen: Shenzhen Huichuan Technology Co., Ltd., 2004. [2] Du Jincheng. Electrical Variable Frequency Speed ​​Regulation Design Technology [M]. Beijing: China Electric Power Press, 2001. About the Author: Engineer Jiang Yong has been engaged in the research and marketing of variable frequency vector control and is currently employed by Shenzhen Huichuan Technology Co., Ltd.