Nonlinear control of pH system for change over titration curve

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.