Research And Implementation Of PID Control System Based On Domestic PLC

Programmable Logic Controller(PLC)is a combination of network communication technology,computer technology and automatic technology,which is a device designed specifically for the field of industrial control and widely used in industrial control site.PLC is not only widely used in general industrial production,but also used in the field of basic energy facilities,so the safety of PLC can not be ignored.For example,the Stuxnet virus on the invasion of Iran's nuclear power is a long-term warning for industrial control safety.Therefore,the developing a completely independent controllable domestic PLC with a perfect control function cannot be delayed.In this thesis,I will study the implementation of PID control system based on the domestic PLC.I Choose the PID control algorithm because PLD control method is very typical and widely used.Modern industry PLC is mostly implemented by PLD and the control function of PID is usually the criterion for measuring the function of PLC.Along with the improvement of the complexity of the technology level and the requirement of controlling,the conventional PID control method is difficult to meet requirement.Relay self-tuning and neural network provide new thoughts to solve this problem.This thesis has done the following aspects:1)The PID control algorithm is studied and the PID control algorithm with deadband and integral separation function is designed and implemented on domestic PLC platform.The design and implementation is realized based on the hardware and software organization structure of the dual-capacity water tank control system.The Double water tank level is controlled by monitor software monitoring site situation;Through test,the PID control system based on domestic PLC can complete double water tank control function.2)In order to solve the problem that conventional PID manual tuning wastes time and energy,the method of relay feedback is designed to tuning the PID parameters.By combining MATLAB / SIMULINK and actually debugging in the double capacity tank control system.Through the experimental test,the relay self-tuning control scheme is proposed,which solves the problem of high time and accuracy;3)Relay self-tuning is a kind of off-line method which cannot ideally control non-liner and time-variant control system.In order to solve this problem,BP neural network algorithm is designed for self-tuning PID parameters.By combining MATLAB/SIMULINK simulation,it is proved that BP neural network has good self-tuning PID control performance,fast response speed,short adjusting time,small overshoot,high reliability,has very high practical values.It has completed actual double water tank control system encoding implementation and site debugging.After experimental test,under the condition that external water lever interfere widely,BP_PID ensure that the level can maintain the set value highly stable fastly and achieve good control effect.