Robustness of discrete-time adaptive controllers: an input-output approach

A general input-output approach that can be used for the design and analysis of robust discrete-time adaptive control schemes is presented. In particular, a model reference adaptive controller is considered. The design approach involves the use of the certainty equivalence principle to combine a robust control structure with a robust adaptive law. Using exponentially weighted I₂ norms and exploiting the properties of the adaptive law and the control structure, robust stability is established for the closed-loop adaptive control scheme