Research On Temperature Control System Of Zinc Pot Based On Fuzzy-PID

In continuous hot dip galvanizing line, zinc pot is the main equipment which can melt zinc ingot, maintain temperature of liquid zinc and realize galvanizing production process. With a series of advantages of high heat efficiency, good operating environment and high control accuracy, induction heating zinc pot is widely used.As a typical case of process control, the dynamic characteristics of the temperature automatic control system of zinc pot have the features of great inertia, large delay and non-linearity, so it is hard to establish precise mathematical model. Based on the above saying, two temperature control methods are compared and simulated.The first method is PID control. It is simple, realized easily and has the advantage to eliminate the steady-state error. In most cases, it can satisfy the control demand. The efficiency of PID control mainly depends largely on its parameters. The parameter adjustment is realized by methods of Ziegler-Nichols, Chien-Hrones-Reswick in this paper. The second method is fuzzy control. It has the distinct advantage of speediness and stability. As a kind of algorithm similar to expert rules, the fuzzy control offers a kind of ideal algorithm for complex control systems. The fuzzy control rule table is established through analyzing the characteristic of zinc pot heating.The PID control system and fuzzy control system are simulated by using Simulink and fuzzy logic tools in MATLAB. Experimental results illustrate that when choosing PID control method is used, system has no steady-state error but regulating time and overshoot can not achieve performance specification at the same time. When choosing fuzzy control, overshoot can achieve performance specification, but system causes steady-state error.The advantages and disadvantages of the two control methods are analyzed and compared in the paper and it comes to the method of combining them together. The parameters of PID controller are adjusted by fuzzy inference. Through simulating and analyzing, the fuzzy PID controller can achieve the system performance specification.On the basis of research achievement, the fuzzy PID control method is applied into temperature automatic control in the condition of available technique and equipment at manufacture field. Based on Siemens S7-300 PLC, the main program flow chart is designed and the function block of fuzzy PID control is written by using ladder logic programming language in STEP 7.Experimental results illustrate that the system can achieve the system performance specification. So the fuzzy PID control is an ideal method to temperature automatic control system of zinc pot.