Robust control of linear time-invariant plants using switching and nonlinear feedback

A number of results are offered as evidence in support of the plant uncertainty principle. There are several important feedback synthesis problems for which the validity of this principle is yet to be ascertained. These include the robust performance problem. Only robust stabilization problems with purely parametric or purely unstructured uncertainty are treated. For the more interesting situation in which both types of modeling uncertainty are present, nonlinear time-varying (NLTV) controllers are, of course, at least as good as, and very likely better than, linear time-invariant controllers. The fundamental issue is then to quantify the superiority of NLTV controllers in terms of quantitative measures of the relative amounts of parametric and unstructured uncertainty