Robust controller synthesis of multivariable system subjected to noises and nonlinear time-varying plant perturbations

A new robust stability criterion is developed to guarantee the stability of the feedback systems subjected to noises and nonlinear time-varying plant perturbations. The main contribution of this paper is an extension of the results of robust stability for the class of feedback systems containing nonlinear time-varying plant perturbations to the class of systems with unstable plants and noises. The generally parameterized stabilizing controller, advanced by Youla et al., is combined with Schur function (class S) to synthesize the robust stabilizers of the feedback systems subjected to noises and nonlinear time-varying plant perturbations.