Conditions for local stability and robustness of adaptive control systems

This paper reports some preliminary results concerning robustness properties of adaptive control systems to unmodeled dynamics and bounded disturbances. The analysis is conducted from the viewpoint of input/output stability theory. Generic representations are proposed for both continuous-time and discrete-time adaptive systems and conditions for stability and robustness are developed for each case. These conditions require varying degrees of a priori knowledge about the plant, e.g., global conditions involving minimal knowledge and local conditions involving more restrictive assumptions.