9412340 Isidori The design of feedback laws for systems characterized by complicated nonlinear dynamical behavior is challenging research task which has attracted an increasing interest in recent years. Advances in nonlinear control theory will substantially improve the design of control systems for light-weighted robot arms, for autopilots and guidance systems of highly maneuverable aircrafts, increase the flexibility and energy efficiency in the regulation of chemical plants, facilitate the real-time reconfiguration of a control system after the occurrence of a failure. Among the many problems which must be confronted, a most important one is the design of feedback laws achieving a prescribed performance objective, usually expressed in terms of the response to a prescribed set of command inputs for the control of a physical system in the presence of substantial model uncertainties. A methodology which, in the case of linear systems, has proven very effective in the design of robust controllers in the presence of unstructured perturbations, is that based on the minimization of the maximal amplitude of the frequency response to exogenous disturbance inputs. The purpose of this research is to contribute to the extension of this design methodology to nonlinear systems and to show how this can be effectively used to address a number of relevant problems which arise in the design of nonlinear feedback laws achieving robust performance. ***
