Robust Control of a Nonlinear Process with System Uncertainty and Delay using Variable Structure

A nonlinear variable structure control strategy is combined with the reaction invariant to control pH in a mixing tank with process delay. A nonlinear predictor is utilized to estimate the actual pH from its measured value. System response is significantly improved by overlaying a variable structure on the controller gains. Uncertainty in the process delay, titration curve and influent disturbance is incorporated into the controller design. Robust controller design is obtained by incorporating a procedure based on the binary classification of the system response to produce system behavior which is insensitive to the given system parameter uncertainty. This procedure provides a practical design of a variable structure controller regulating a system with significant process delay where the system state is not directly available.