Linear Control of Nonlinear Processes: The Regions of Steady-state Attainability

Despite the fact that most processes are intrinsically nonlinear, linear controllers are still widely favored in process-control applications. In this paper, we provide an analytical framework to assess the viability of applying linear control to stable nonlinear processes based solely on the process nonlinear steady-state information. Steady-state information is usually available from the process flowsheet; hence, the analysis described in this paper can be used as a tool for operability studies during process design. We define two operating spaces of interest: the steady-state region of attraction under linear control and the steady-state achievable output space via feedback. We show that these operating spaces provide an extension to a recently proposed steady-state operability analysis (Vinson, D. R.; Georgakis, C. A. J. Process Control 2000, 10, 185-194). Using the same steady-state information, we obtain additional insights into the range in which a linear controller can achieve offset-free control.