Robustness of Multivariable Smith Predictors

Stability and stability robustness of multivariable Smith predictors are analysed by viewing Smith predictors as instances of Internal Model Control. This allows a much simpler development than appears in previous analyses, and the way that delays enter the plant transfer function matrix is unrestricted. It is shown that robustness to additive plant perturbations can be predicted during design, on the basis of a model of the rational part of the plant alone. A design example based on the Shell Control Problem is included.