A model-based control method applicable to unstable, non-minimum-phase, nonlinear processes

This paper presents a nonlinear control system that is applicable to stable and unstable processes, whether non-minimum- or minimum-phase. The closed-loop stability is ensured by forcing every process state variable to follow a desired linear response. This approach results in a nonlinear state feedback that induces approximately linear responses to the state variables. The control system includes the nonlinear state feedback and a reduced-order nonlinear state observer. The application and performance of the control system are shown by implementing it on a chemical reactor with multiple steady states. The control system is used to operate the reactor at one of the steady states, which is unstable and non-minimum-phase. The simulation results show that the closed-loop system is asymptotically stable for all physically-meaningful initial conditions.