Nonlinear Control of pH System for Change Over Titration Curve

D. Swati, V. S. R. Rao, R. Pickhardt and M. Chidambaram

Abstract
Wiener model based nonlinear controller for a pH process efficiently tackles the variations in gain. However, the controller performance deteriorates for significant change over titration curve (i.e. when the nature of the feed stream switches from a weak acid to a strong acid). To improve the performance of this controller, a nonlinear cascade controller is proposed. The nonlinear cascade structure consists of a Wiener model based nonlinear P controller in the inner loop and a linear PI controller in the outer loop. The proposed strategy is simulated for switch over titration curve from a weak acid – strong base system to strong acid – strong base system and then back to the weak acid – strong base system. The performance of the nonlinear cascade controller is compared with that of single loop Wiener model based PI controller and linear cascade (P-PI) controller.

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Keywords
pH effect, Wiener model, nonlinear cascade structure, strong acid, weak acid