Sliding mode variable structure control for smith prediction monitoring AGC system based on double power reaching law

Abstract

To overcome unfavorable influence of the large time delay existing in monitoring automatic gauge control (AGC) of tandem hot mill and model mismatching greatly on strip rolling process on system stability, a sliding mode variable structure control for Smith prediction monitoring AGC system based on double power reaching law was designed. The mathematical model of the hydraulic gap control (HGC) system was established based on the 7# stand in 1450 mm tandem hot mill of a factory and model parameters were identified by Levy curve fitting method. Based on the identified model, conventional Smith prediction monitoring AGC system (SP-MNAGC), sliding mode variable structure control for Smith prediction monitoring AGC system based on constant rate reaching law (CR-SPSMC-MNAGC) and sliding mode variable structure control for Smith prediction monitoring AGC system based on double power reaching law (DP-SPSMC-MNAGC) were researched with Matlab/Simulink software. The results show that the three different controllers acquire good control effect during model matching. But during model mismatching, for SP-MNAGC system, the maximum value of rising time will increase to 2102.3 ms, the overshot will increase to 39.6 %; for CR-SPSMC-MNAGC system, the maximum value of rising time will increase to 348.3 ms, the overshot will increase to 13.1 %; for DP-SPSMC-MNAGC system, the overshot is less than 8.7 %, and the rising time is less than 36.1 ms in any case. Besides this, DP-SPSMC-MNAGC system can weaken the chattering of sliding mode effectively.