| Temperature control of the silicon rod surface in the reduction furnace ofpolycrystalline silicon plays a significant role in the production of polycrystallinesilicon and even the development of the entire photovoltaic industry. The surfacetemperature of the silicon rod has to be maintained at the optimal reaction temperature,and the fluctuation should not be violent. Due to the change of the electrical structureof the silicon rod as a result of the vapor deposition reaction in the production ofpolycrystalline silicon, temperature control of silicon rod at present mainly employsopen-loop control which involves intense labor. In light of the problem, this papercomes up with the double closed-loop control system with model-free adaptive fuzzycontroller as the major controller and PI as the auxiliary controller. It adopts thestructure of model-free adaptive controller and carries out on-line revision of itsparameters by means of fuzzy rules, which not only ensures the convergence andstability of the temperature control system, but also enhances the rapid dynamicperformance of the system toward temperature control.This paper first explains the chemical reaction mechanism of the silicon rodtemperature in the reduction furnace of polycrystalline silicon. It selects the phase dheating power as the heating power for the silicon rod, and the third-order timevarying nonlinear transfer function of the controlled object is deduced. Estimation ismade on the parameters of the transfer function. Based on the electrical characteristi csof the silicon rod in the course of sedimentation, the large time-varying parametersystem is decided. despite the fact that,the transfer function serves as the basis for thecomparison and selection of the major controller. Next, make the traditional P ID andthe model-free adaptive controller as the major controller of the double closed-loopcontrol system respectively, conduct a comparative study of the dynamic and steadystate performance of the control system, and adopt an simulation approach to deci dethe limitation of the traditional PID toward the large time-varying parameter system.On the other hand, despite the fact that the model-free adaptive controller is able toensure the stability and convergence of the time-varying parameter system, thesimulation test shows that its dynamic performance is subjected to the influence of thecontroller and the controlled object, which does not meet the requirement ofthermostatic control for the silicon rod. Therefore, based on the influence of theparameter learning factor and step sequence of the model-free adaptive controller onthe dynamic performance of the system, this paper takes advantage of the fuzzy adaptive approach and uses errors and error change rate to decide the two parametersof learning factor and step sequence. Simulation test reveals that the improvedmodel-free adaptive controller can converge to the set value regarding thetime-varying parameter system more rapidly than the common model-free adaptivecontroller, with small overshoot, enhanced dynamic performance and almostunchanged steady-state performance. Therefore, adopting the model-free adaptivecontroller featuring fuzzy adaptation can meet the requirements of the temperaturecontrol for silicon rod and the feasibility of the improved model-free adaptivecontroller as the major controller is testified in the simulation test. In addition, thethesis designs how to realize the sampling of current, voltage and temperature,introduces the hardware structure of control system with S7-300as its core, explainsPLC module selection and system network communication based on the technology ofPROFIBUS-DP and MODBUS, then it elaborates the pulse triggering circuit with aSCM-PIC16F1936as the core. Finally it makes hardware configuration arou nd thecore hardware system-S7-300by Step7software and realizes control systemalgorithm through STL language and designs the software program frame of SCM. |
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