Adaptive output feedback nonlinear control of a pH process with an input constraint

An adaptive output feedback nonlinear control scheme is presented for a pH process, which is difficult to control due to the nonlinearities and uncertainties. A nonlinear controller is designed using a backstepping technique to handle the pH process with an input constraint. The backstepping-based controller is combined with state and parameter estimators to deal with unmeasurable state variables and unknown parameters, thereby resulting in an adaptive output feedback nonlinear controller. The input constraint mentioned above is considered in the controller and estimator designs. The stability properties of the proposed scheme are given, and simulation results show that uniform closed-loop performance is obtained despite the nonlinearity, the uncertainties of the parameters, and the unavailability of the state variables.