Adaptive nonlinear control of a pH neutralization process

An adaptive nonlinear control strategy for a bench-scale pH neutralization system is developed and experimentally evaluated. The pH process exhibits severe nonlinear and time-varying behavior and therefore cannot be adequately controlled with a conventional PI controller. The nonlinear controller design is based on a modified input-output linearization approach which accounts for the implicit output equation in the reaction invariant model. Because the reaction invariants cannot be measured online and the linearized system is unobservable, a nonlinear output feedback controller is developed by combining the input-output linearizing controller with a reduced-order, open-loop observer. The adaptive nonlinear control strategy is obtained by augmenting the non-adaptive controller with an indirect parameter estimation scheme which accounts for unmeasured buffering changes. Experimental tests demonstrate the superior performance of the adaptive nonlinear controller as compared to a non-adaptive nonlinear controller and conventional PI controller