Design of fuzzy control for maintaining a CSTR in the steep section of itsnonlinear characteristic

The operation of a continuous stirred tank reactor (CSTR) in the steep doma in of its nonlinear process characteristic is studied, using catalyzed hydr ogen peroxide decomposition as a model process because of its transparent n onlinear dynamics. Unstable equilibrium states and corresponding limit cycl es exist in the steep domain, the latter representing dynamically stable mo des of operation where safer control is expected due to the lower educt con centration in the reactor. For CSTR control in the steep domain, a fuzzy ap proach is applied based on simulations and experimental understanding of th e stable and unstable states of the reactor. Simulations are carried out fo r the set-point control of an unstable equilibrium state, and the tracking control of the corresponding stable limit cycle. The simulation results sho w that operation in the limit cycle requires much less control energy than that of the corresponding unstable equilibrium state in the case of disturb ances, e. g., due to unavoidable modelling errors.