Research On New Control Strategies Of Large PVC Device Reaction Temperature

Polyvinyl chloride (PVC) have been widely used in various industries, and it plays an important role in the national economy. One of the key factors which determine the quality of the product is PVC polymerization temperature. PVC polymerization reaction is the exothermic and batch reaction. The mathematic model has difficulty in establishing because the reactor has the characteristic of nonlinearity, uncertainty and the external interference. But the requirement of temperature control is quite strict. At present, the temperature control methods of PVC is still PID, but the traditional PID controller could not achieve the desired requirements. It could result in increasing the adjustment time and the amplitude of temperature oscillation, which seriously affects the quality of the product. In this thesis, the new control strategies of PVC device reaction temeperature are proposed. The main work of this thesis are as follows:(1) According to the PVC production process and the reaction mechanism of polymerization, the polymerization reaction and the factors which affecting the temperature control at all stages of the process are detailed analyzed in this thesis Then the difficulties of the reactor temperature control are summarized. According to the polymerization reaction dynamics and the balance equation of energy and material, the relation function of reaction temperature and jacket temperature is caculated. The parameters of the function are identified by the least square identification, and then converted to state-space form. Then the accuracy and validity of the model are confirmed by the on-line correction and off-line verification, which is the prepared for the controller design.(2)According to the different dynamic characteristics of the temperature of polymerization reactor, the minimum variance covariance constrained controller is designed for the temperature heating stage and holding stage. Then minimize the controller performance indicators with LMI(Linear Matrix Inequality) based on the given input variance and the output variance. We can get the optimal feedback controller law. At the two stage of temperature the controller can switch without disturbance by the single increasing bound controller switching algorithm and it applies to the actual industrial production, the results show the validity and the feasibility of research methods.(3)In the case of serve external disturbance, the linear parameter variation modeling method for the whole polymerization temperature is proposed. The research method through serveing external variables as scheduling variables, describe the global dynamic characteristics of controlled plant corresponding the track of scheduling parameters. Through linear fractional transformations(LFT), the uncertain factor can be stripped out of the original system for consideration. In this way, the designed controller is able to meet the control requirements perfectly in the trajectory of the scheduling parameters.(4) Aiming at the actual industry it is difficult to judge the controller performance one by one. This thesis developes the control system performance evaluation software by C# based on sensitivity function and complementary sensitivity function of the closed-loop plant. And the instructions of the software have carried on the detailed explanation.