ABSTRACT
This chapter considers the standard feedback control system. However, if the controller designed for the nominal model does not take into account the approximation errors (called plant uncertainties), then the feedback system may become unstable when this controller is used for the actual plant. It introduces ℋ∞-based controller design techniques for systems with dynamic uncertainty. The chapter reviews modeling issues discussed and give additional examples of unmodeled dynamics, and illustrate again how to transform a parametric uncertainty into a dynamic uncertainty. For unstable plants, a similar parameterization can be obtained, but in that case, derivation of the controller expression is slightly more complicated. An immediate application of the Youla parameterization is the robust performance problem. For stable time delay systems there is a popular controller design method called Smith predictor, which dates back to 1950s. The chapter presents solution for the H∞ optimal mixed sensitivity minimization problem.
