ABSTRACT
This chapter discusses different configurations of model reference adaptive control (MRAC) systems and deals with the classification of MRAC systems. It provides the mathematical description of MRAC systems and considers an equivalent representation of an MRAC system as a nonlinear time-varying system. The chapter examines that the relevant equations are formulated for the direct and indirect MRAC systems. A model reference adaptive system can be represented by an equivalent nonlinear time-varying system such that it is reduced to a standard feedback system having a linear part in the feed-forward path and a nonlinear time-varying part in the feedback path. The main difference between indirect and direct adaptive control lies in the following two facts: First, a model of the desired behavior is explicitly used in direct control whereas a model of the plant identified on-line is used in indirect control. Second, identification error in indirect control and the control error in direct control are used to update the controller parameters.
