Robust nonlinear internal model control of stable Wiener systems

Many process systems can be modeled as a stable Wiener system, which is a stable linear system followed by a static nonlinearity. A nonlinear control design procedure is presented that provides robustness to uncertainties while being applicable to systems with unstable zero dynamics, unmeasured states, disturbances, and measurement noise. The design procedure combines nonlinear internal model control with linear matrix inequality feasibility or optimization problems, such that all robust stability and performance criteria are computable in polynomial-time using readily available software. Application to a pH neutralization case study demonstrates the importance of taking uncertainty into account during the design of controllers for Wiener systems. The approach is generalizable to Hammerstein and sandwich systems, whether well- or poorly conditioned, and to systems with actuator constraints. (C) 2012 Elsevier Ltd. All rights reserved.