Unification of some discrete-time adaptive control schemes

Adaptive control can be approached from many different points of view. In recent years there has been much progress made both on model reference adaptive systems (MRAS's) and on self-tuning regulators (STR's). The two approaches are treated here in a general framework. It is shown that MRAS's can be derived from the STR point of view. Special attention is paid to the positive real condition, which appears in the analysis of both types of schemes. It is shown that this condition can be dispensed with in the deterministic case.