A continuous stirred tank reactor operating under digital computer control has been designed and built, and a comparison made between digital control methods that employ recent advances in estimation theory, and an equivalent classical analog control system. The digital control method required process identification, optimal control, and Kalman filtering for its implementation. The unknown parameters in the nonlinear mathematical model describing the process were identified by the method of quasi-linearization. This technique not only linearizes the non-linear system equations but also provides a sequence of functions that in general converge rapidly to the solution of the true non-linear equations. The optimal controller is believed to be original and comprises an adaptation of the quasi-linear algorithm. The controller calculates, at preset time intervals, those changes in the desired values of supervisory feedback controllers such that a weighted sum of squared errors at the end of the time interval is minimised. The predicted value of the state vector obtained in this calculation was then used in a fixed gain formulation of the Kalman filter. Simulation studies verified the viability of both the identification and optimal control methods, which were then applied to the process. The classical controller was designed using either the method of Ziegler and Nicholl or that of Bode, which utilised the frequency response. Experimental work showed good agreement with the simulation studies. However, it was found that the Kalman filter was unnecessary because of the essentially noise-free nature of the measurements. The identification method performed satisfactorily, and gave the values of the parameters in the mathematical model which described the process. The digital control system was shown to give better control than the classical scheme, especially in the steady state, where the predictive nature of the optimal controller effectively prevented overshoot, whilst assuring a fast stable response to disturbances.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:463370 |
| Date | January 1975 |
| Creators | Litchfield, R. J. |
| Publisher | University of Surrey |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://epubs.surrey.ac.uk/847648/ |
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