Robust stabilizability of linear plants under time varying and nonlinear perturbations

The problem of robust stability of linear feedback systems in the presence of time varying and nonlinear perturbations is considered. The basis of the characterizations of robust stability consists of linear fractional transformations which relate possibly unstable and nonlinear perturbations and perturbed plants to stable systems. For nominal finite-dimensional linear time invariant plants subject to a family of linear time varying perturbations the author obtains such a characterization and derives conclusions about robust stability