GAIN-SCHEDULING TRAJECTORY CONTROL OF A CONTINUOUS STIRRED-TANK REACTOR

The control of continuous stirred tank reactors is often a challenging problem because of the strong pronounced nonlinearity of the process dynamics. Exact feedback linearization and gain-scheduling are two wel l-known approaches to the design of nonlinear process control systems. The basic idea in this paper is to combine these techniques to obtain a control structure which preserves the advantages and overcomes some of the problems of the two concepts. In a first step, a nonlinear sta te feedback controller is computed by exact linearization of the proce ss model to shape the nominal closed-loop system. The required unmeasu rable state variables are obtained by simulation of the process model. This part of the controller thus is a pure nonlinear feedforward comp ensator for the nominal plant. To act against disturbances and model u ncertainty, a nonlinear gain-scheduled controller is designed by appro ximately linearizing the process model not for a number of operating p oints as in the standard gain-scheduling approach but around the nomin al trajectory generated by the nonlinear feedforward controller. The d esign approach is applied to a non-trivial concentration control probl em in a continuous stirred tank reactor with nonminimum phase behaviou r, unmeasurable states, and model uncertainties as well as unknown dis turbances. The nonlinear control structure is compared to a linear con troller and to a pure gain-scheduling controller and shows excellent p erformance even for worst case disturbances and model uncertainties. ( C) 1998 Published by Elsevier Science Ltd. All rights reserved.