Abstract : To address the problems existing in continuous casting production, a variable frequency speed control system was designed to replace the DC speed control system. The system composition and operation process are described, realizing the control of the frequency converter by the PC and the interlocking control between the two frequency converters. A flowchart of the PC control program is also provided. Actual operation results show that the new system is safe, reliable, has a low failure rate, and outperforms the original DC system. Keywords : Variable frequency speed regulation; continuous casting; programmable controller [b]1 Continuous casting straightening process flow and its DC speed regulation system 1.1 Continuous casting process flow[/b] The continuous casting workshop of Kunming Iron and Steel Group's No. 2 steelmaking plant has two R6m full-arc type four-strand continuous casting machines. The process flow of its straightening vibration transmission system is as follows: When feeding the ingot, the straightening machine reverses to send the ingot rod to 500mm below the crystallizer. Then, the straightening machine is jogged to send the ingot rod into the crystallizer. When pouring, the straightening machine rotates forward to pull out the ingot rod and the billet. At the same time, the vibration motor rotates to drive the crystallizer to vibrate up and down. The billet speed is adjusted by the positioning potentiometer for pouring. The vibration frequency is kept constant with the billet speed. [b]1.2 DC speed regulation system composition[/b] The continuous casting straightening electrical transmission system is composed of a DC speed regulation system. Its equipment configuration is: one straightening motor and one vibration motor. They share one set of thyristor DC speed regulation device. The system composition diagram is shown in Figure 1. [b][align=center]For details, please click: Application of Variable Frequency Speed ​​Control in Continuous Casting Retrofitting[/align][/b]