What strategies are used for controlling highly nonlinear processes?

Nonlinear control strategies: gain scheduling (tune at multiple operating points, interpolate parameters), feedback linearization (transform nonlinear system to linear), variable structure/sliding mode control (robust to parameter variations), neural network control (learn nonlinear relationships), nonlinear MPC (use nonlinear models in optimization), and fuzzy logic (rule-based expert system approach). Implementation considerations: model accuracy requirements, computational demands, commissioning complexity, and maintenance capability. pH control exemplifies extreme nonlinearity - titration curve gain varies 1000:1 requiring special techniques like adaptive or reagent-demand control.