Abstract : This paper applies PLC-controlled variable frequency speed regulation to the tension control of a rolling mill. It elucidates the principle and system composition of constant tension control in the coiler within the sIMOVERT MASTERDRIVES AC vector control system. The key to this design is the use of vector control. The current detected from the stator side undergoes a 3/2 transformation and vector transformation to obtain a torque signal M, which serves as the actual torque feedback signal, thus achieving constant linear speed, i.e., constant tension. The high-precision and high-quality torque dynamic control effect of sIMOVERT MASTERDRIVES meets the production process requirements of plate and strip steel. Keywords: Variable frequency drive, tension control, coiler, cold rolling mill, control system 0 Introduction With the rapid development of modern industrial technology, the requirements for the variety, specifications, and output of plate and strip steel are increasing. In China, single-stand four-roll reversible strip cold rolling mills occupy an important position. Due to the advantages of DC drive systems, such as good speed regulation performance, simple circuitry, convenient control, strong overload capacity, and ability to withstand frequent impact loads, they are widely used in current speed regulation systems. With the rapid development of power electronics, microcomputer, and automatic control technologies, frequency conversion speed regulation has become a trend in replacing DC speed regulation. Compared with traditional DC speed regulation, it has advantages such as simple structure, robustness, durability, economy, reliability, and convenient installation and maintenance. In the renovation project of a cold-rolled strip steel mill, Siemens SIMOVERT MASTERDRIVES frequency converters were used to achieve indirect coiling constant tension control. 1. Basic Principles and Methods of Constant Tension Control In strip and steel production lines, to ensure tight and even coiling and improve product quality, it is necessary to maintain constant tension between the coiler and the tension roll. Therefore, such control systems are designed as tension adjustment systems. Cold rolling of steel strip is impossible without tension. Tension reduces rolling pressure, improves strip shape, and stabilizes the rolling process, making it crucial for cold strip rolling. Figure 1 shows a schematic diagram of the strip coiling system. During the coiling process, the tension between the coil and the main machine should be kept constant. This system uses a SIMOVERT MASTERDRIVES vector control frequency converter to control a three-phase asynchronous motor, achieving constant tension control during strip coiling. [b][align=center]For details, please click: Application of SIMOVERT in Cold Rolling Mill Coiling Control System[/align][/b]