[ Abstract ] This paper introduces the application of a large AC-AC frequency converter in the main drive of the Panzhihua Iron and Steel Group's hot rolling mill, and elaborates on the composition and control functions of the main drive control system. [ Keywords ] AC-AC frequency converter; main drive; system composition; control function The Panzhihua Iron and Steel Group's hot rolling mill was put into operation in 1993. Due to the inability of the drive system's response and control performance to meet production needs, the improvement of product quality was affected. Therefore, its control system underwent technical transformation, adopting an AC-AC frequency converter synchronous motor digital vector control system. 1. Composition of the Main Drive Control System The main drive AC-AC frequency converter synchronous motor digital vector control system consists of six AC-AC frequency converter main cabinets, one excitation cabinet, one SIMAKYND control cabinet, one relay cabinet, and three absorption cabinets. The single-line diagram of the main circuit is shown in Figure 1. The stator main circuit consists of a high-voltage circuit breaker, rectifier transformer, three-phase AC-AC frequency converter, fast-opening and no-load disconnector, AC synchronous motor, etc. The rotor main circuit consists of a circuit breaker, incoming line reactor, excitation rectifier, etc. The rectifier transformers are connected in a d/dO, d/y11 configuration, ensuring a certain electrical angle difference in phase between the secondary windings to reduce grid harmonics. The motor's excitation windings are powered by four rectifier transformers: two for the roughing mill's R2 upper and lower rollers, and two for the finishing mill's F1-F6 rollers (one for standby). Each motor's rotor excitation circuit is powered by a separate six-pulse rectifier bridge. Each frequency converter consists of six thyristor cabinets; two frequency converters are connected in parallel to form a single-phase frequency converter, divided into master and slave cabinets. Each cabinet is a three-phase bridge-type anti-parallel single-phase output AC-AC frequency converter. The six single-phase AC-AC frequency converter cabinets form a three-phase AC-AC frequency converter with a Y-connected output. The motors are DC-excited salient-pole rotor AC synchronous motors with Y-connection. [b][align=center]For more details, please click: Application of Large AC-AC Frequency Converters in Main Drives of Hot Rolling Mills[/align][/b]