Closed-Loop Identification and Control of Multivariable Chemical Processes: a Case Study
Closed-loop identification methods based on relay techniques have been analyzed and compared with open loop methods for an application to a multivariable nonlinear chemical process (a distillation unit: C 3 — C 4 splitter). Classical relay techniques and a recently proposed method for identification and control design (ATV+) are applied in a sequential procedure which leads to the design of decentralised controllers.
Several disadvantages of open-loop identification techniques have been put into evidence, mainly the inconsistency of the obtained results in the case of a non linear process (model parameters depend on the amplitude of the perturbations used during the identification). Also, longer times are necessary for the experimental tests and a more complex controller tuning technique is required. Closed loop relay techniques are faster, identify the real dynamics of the system and allow a more direct design of the control system. The ATV+ technique can be successfully applied to the process under study, after some modifications made necessary by the nonlinear nature of the system.
KeywordsDistillation Column Manipulate Variable Process Gain Transfer Function Model Closed Loop Performance
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