Research Of Liquid Level Fuzzy Control System Based On TWINCAT Platform

In this paper, liquid-level control system is researched object. The conventional PID controller has simple arithmetic and good robustness. It is widely used in indust process control systems,but the controller has some limitations. Because the PID parameters can not be adapted in such controller on line when the parametrer of object controlled has changed. The liquid level control systems have always the quality of big inertia, nonlinear, time-lag. In this system the conventioal PID controller can not get satisfying control require, and fuzzy controller is based on knowledge and independent of accurate mathe model. So, the combination of fuzzy controller and PID controller has certain practical value in the application of liquid level control system. The two controllers'advantage is used in the combination method.The structure of PID control, Fuzzy control and Fuzzy self-adaptive PID control has been studied. It is analysised that the quantification factor of error ,the quantification of error change and proportionality factor influence on the control sysytem . The"ACSK"integrated experimental equipment and the TwinCAT platform based on PC-based control technology are introduced in this experiment, and the platform is designed by Germany BECKHOFF company. In addition, PC-based control technology and Profibus-DP communication protocol has been described a little. The mathe model of water tank of liquid control system is set up by using the step response method.During the development of this program, the control program is compile with VC++ and TwinCAT which afford special interface for the VC++. The Fuzzy control algorithm and the interface of person and machine are completed by hybrid program.Finally,in view of the parameters time-variation feature of the process object and experimental system, Fuzzy controller and Fuzzy self-adaptive PID controller are designed. The all controllers are simulated by using Matlab/Simulink and all effects of those are compared . The simulation result indicates that Fuzzy controller which is compared with PID controller has good dynamic and static performance , Fuzzy self-adaptive PID controller has robuster character and the effct of fuzzy controller with correction factor rests with correction factor. Experimental result indicates that Fuzzy controller is good dynamic and static performance by comparing with the traditional PID controller.