A Study on Design of Process Control System in the Presence of Load Change

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The aim of this research is to develop a design method of digital tracldng control system for chemical plants in the presence of large load changes. We direct much attention to the fact that the chemical processes of interest are subject to time-delays, nonlinearities, and direct link between the control input and output. The following are the findings of the present research.1. Based on the LQI technique, we derive an optimal digital controller having integral, state feedback plus preview action.2. For a special case of importance where the time-delay is unilateral, we develop an algorithm to compute feedback gain with less computational effort.3. We apply the above control algorithm to a control of a pilot heat exclianger plant, where the purpose is to regulate the water outlet temperature and flow rate independently to follow the given references without steady state errors.4. We present a design method of a nonlinear control system combining an exact input-output linearization technique and the tracking control algorithm of developed above.5. We apply tlie above technique to a tracking control of a nonlinear continuous stirred tank reactor(CSTR)with a time-delay and in tlie presence of large load changes. Simulation studies show the effectiveness of the present algorithm. Tlie robustness of tlie resulting control system is checked by simulations by giving perturbations of <plus-minus>20% to nominal paraineter6. During this research, we understand the importance of developing a technique for checking a robustness of a resulting nonlinear control system, since at present there exists no methodology to evaluate the robust stability of a nonlinear tracking control system.