A comparison of nonlinear control techniques for continuous stirred tank reactors

✍ Scribed by Phani B. Sistu; B. Wayne Bequette

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 548 KB
• Volume: 47
• Category: Article
• ISSN: 0009-2509
• DOI: 10.1016/0009-2509(92)87092-5

✦ Synopsis

Globally linearixi ng control, a differential geometry-based technique (continuous), and nonlinear predictive conuol, an optimization-based approach (discrete), are compared for temperature control of a classical exothermic CSTR The two strategies can be tuned to have identical performance for setpoint changes or measured disturbances when there are no bounds on the manipulated variable. As the sample time is deca the two performance for unmeasured disturbances or uncertain models. approaches also yield identical However, NLFC pc4fom18 beater in the presence of constraints on the manipulated variable. An open-loop observer for the unmcasurcd state variable (composition) has been used. The system studied is minimum-phase, allowing a filtered deadbeat control law for the nonlinear predictive control strategy. MOTIVATION Chemical reactors create some of the most challenging feedback control problems faced by chemical process control engineers. Complex static and dynamic behavior, such as input or output multiplicities, ignition-extinction behavior and parametric sensitivity create challenges that are tough for traditional linear controllers to handle. An excellent review of multiplicities and instabilities in chemical reacting systems is provided by Raxon and Schmitx (1987). During the past five years there have been a number of control strategies developed that are based explicitly on a nonlinear process model. These nonlinear control strategies can be conveniently lumped into two categories: (i) differential geometry-based control and (ii) optimization-based control. A tutorial review of differential geometry-based control techniques has been provided by Kravaris and Kantor (1990); a comprehensive review of nonlinear control is presentedby Bequette (1991).