ABSTRACT
In this paper we review recent results obtained by the author and his coworkers, on the robust stability of control systems containing uncertain real parameters as well as those containing mixed types of perturbations. These take the form of simultaneous uncertainty in real parameters as well as unstructured perturbations of the H ∞ norm bounded type or nonlinear sector bounded feedback type. The results, which are given here without proofs, deal with the calculation of parametric, H ∞ and nonlinear sector bounded stability margins and highlight the importance of certain extremal segments and manifolds where the maximum and minimum values of these margins occur. They are applicable to analysis problems (fixed controller, uncertain plant) and design problems (adjustable controller, fixed plant) and lay the foundation for the full scale development of robust control theory for systems subject to real parameter as well as mixed types of uncertainty.
