The aim of robust adaptive control is to realize satisfactory performance in adaptive systems when various classes of perturbations are present. Examples of such perturbations include bounded disturbances, time- variations in plant parameters, and unmodeled dynamics in the plant. While the behavior of adaptive systems in the presence of bounded disturbances is currently well understood and powerful results have been derived, robustness in the presence of parameter variations and unmodeled dynamics has been established only under assumptions that are quite restrictive. The proposal addresses robustness in the presence of the latter two perturbations and is aimed not only at relaxing these assumptions but also at developing a general set of conditions under which the adaptive system exhibits satisfactory behavior. In the discussion of each problem, the current status of research is first stated, followed by the approach that is proposed and the adaptive procedure that will be employed. In each case, a global analysis of the underlying nonlinear system will be carried out and attempts will be made to derive sufficient conditions for global boundedness of solutions as well as conditions under which the system can have unbounded solutions. The aim of the research is to develop better methods for the design of practical adaptive controllers which can meet stringent performance requirements.
