Research And Design Of Fuzzy Temperature Controller Applying To MOCVD

Due to the special structure of heating equipment and the difficult heating mechanism, the electric heater in MOCVD (Metal Organic Chemical Vapor Deposition) equipment has the characteristics of large delay,nonlinear and has the difficulty to build an accurate mathematical model. The use of traditional PID (Proportion Integration Differential) temperature control strategy often produces overshoot phenomenon,which makes it hard to obtain the ideal control effect. The advantage of fuzzy control is that it does not need to establish accurate mathematical model of the controlled object and has certain adaptation ability to the the delay, nonlinear and non-stationary controlled object and has smaller overshoot and a good robustness.This paper proposes a kind of adaptive temperature control algorithm with correction factor for electric furnace in MOCVD equipment, compared to the traditional PID control strategy. It studies the fuzzy control mechanism and the theory of fuzzy reasoning algorithm.Then determine the structure and control process of the fuzzy controller. Through the analysis of the influence of the temperature deviation and deviation change rate on heating furnace temperature,build a fuzzy control rule table. According to the fuzzy control rule table,finish the simulation and debugging of the whole fuzzy control scheme,which provides a basis to further improve the MOCVD temperature control system. The main work of this thesis includes:According to the basic structure and features of MOCVD electric,in combination with the design requirements of the heater and the experiment environment and test condition,propose the scheme of the design ideas and frame of fuzzy temperature control.Research the principle of the PID and the fuzzy control algorithm,simulate the two algorithms,and give a analysis and comparison to the results. Then determine the advantage of the fuzzy control in delay systems.And through the analysis of the influence of the membership function, different rules and algorithm to the fuzzy control system,determine an adaptive fuzzy control scheme suitable for the heater temperature control.Simulate and analyze it.Build a fuzzy control lut for the electric heater temperature control system in MOCVD with MATLAB. Program the whole fuzzy temperature control program in PLC including signal acquisition, input quantity fuzzification algorithm, fuzzy control query procedures and control signal output procedures.Simulate whole program using PLCSIM software.And debug the program in equipment at the set temperature point10℃,50℃and90℃. Compare and analyze the debugging results with PID controlThe result shows that at90℃,the fuzzy temperature controller takes7minutes for temperature rise and becomes stable after8minutes.The percentage of overshoot is-1.2%,smaller than PID’s2.9%,which shows the overshoot is smaller and stability is higher in delay system.So the fuzzy temperature control strategy in this paper has certain control precision, reliability and stability, which has the possibility to replace PID meter in temperature control.