Fuzzy Control And Its Simulation Research In Liquid Level Control

Liquid level control is one of the typical control in industrial process control, in the early days most used method of the liquid level control in industrial process is PID control method. Conventional PID controller has many advantages, for example its algorithm is simple, it is reliable and non-static. The core of which is setting parameters, the uncertainty object can achieve satisfactory control results through proper tuning three parameters of PID; but to the large lag,the time-dependent,nonlinear complex systems, it is difficult to tune the PID parameters so that it is more difficult to achieve the desired results. Fuzzy controller has outstanding merits that do not rely on math model of object and whose adapting ability is strong, but its static accuracy is poor. On the base of study of lots of home and abroad thesis, combined with Fuzzy-Control and other control method is presented aiming at the above problems, and make a simulation study to different types of typical Level-Model.Firstly, features and development of fuzzy control is introduced simply , its limitations is presented; Then respectively aiming at the time-dependent and large log level object, methods combined with fuzzy control and PID and combined with fuzzy control and predictive control is determined, and also these two methods is introduced necessarily.Secondly, dynamic characteristics of level object are analyzed, dynamic model of single-capacity water tank and double-capacity water tank are deduced.Thirdly, the effect when variable parameters used in PID control algorithm step-response curve of the simulation is not very satisfactory; An adaptive fuzzy-PID control strategy is proposed, which can optimize the controller parameters in real time, make it more adaptable for the model parameters, and control the time-dependent level object preferably, the simulation results show that this system has better features than conventional PID.At last, based on the discussion of fuzzy predictive control mechanism, aiming at large log,time-delay level object, composite method combined fuzzy control and predictive control is presented. The dynamics of the prediction term is adaptive to the system's time delay. Simulation results illustrate that this method is well adaptive to the alteration and improves the static precise and dynamic performance of the system. It is better guidance to actual level control.