The Study On The Dynamic Model And The Control Method Of Hydraulic AGC System

According to problems associated with the inaccuracy of process mathematical model and poor adaptation and long setting debugging period of conventional PID controllers, a new parameters self-adjusting fuzzy PID controller designed by using the Fuzzy Logic Toolkit of LabVIEW in the rolling mill simulator is proposed based on the fuzzy PID theory in this paper, the run results proved the feasibility in AGC system after comparing with the conventional PID controller.AGC is an important method for rolling mill to improve the thickness accuracy of plate-strip. Because the qualified products depend on the uniformity of strip's vertical thickness, AGC has become an indispensable part in Mill Automatic System.In this paper, on the analysis of the hydraulic AGC system and operation mechanism in a strip mill, the mathematical model of electric-hydraulic position control system is built according to the equation of loading pressure-flux in servo value, the equation of loading flux in hydraulic cylinder and the equation of force equilibrium in hydraulic cylinder. However, the complexity of rolling process and the variety of material's thickness bring many difficulties to the accurate mathematic model of AGC. Though those problems place obstacles to the application and implementation of traditional control theory, intelligent control technology provides an effective means for solving the thickness of automatic control.Then, based on applying the fuzzy control theory to the thickness control system after analysising the rolling process deeply, a parameter self-tuning fuzzy PID controller with is designed by using Fuzzy Logic Toolkit and PID Toolkit of NI's graphical programming software LabVIEW, as soon as compiling corresponding program, then the AGC based on fuzzy control theory has implemented.The fuzzy PID controller is made up of PID controller and parameters self-tuning mechanism. The fuzzy controlling theory and methods are used in fuzzy self-adjusting agency. According to the input signal of the actual response, namely changes of the error e and the change of error ec,KP, KI, and KD are adjusted on line complying with the relevant decision based on the fuzzy reasoning. This fuzzy PID controller not only has the merit of flexibility and adaptability, but also keeps the high precision of PID controller.Experimental effects make clear that the improved AGC has good parameter self-adjusting performance, largely improving the accuracy of thickness controlling and overcoming problems such as long adjustment period and overshoot. This improved AGC can better satisfied the requirements for modern automatic thickness control system in rolling industry and lay a good foundation for worksite application.