ABSTRACT

An adaptive control system is a system which adjusts automatically on-line the parameters of its controller, so as to maintain a satisfactory level of performance when the parameters of the system under control are unknown and/or time varying. An adaptive control system is inherently nonlinear, since the controller parameters are nonlinear functions of the measured signals through the adaptation mechanism. Model reference adaptive controllers can be either direct or indirect. The essential difference between them is that in direct model reference adaptive control (MRAC) the controller parameters are directly adjusted by the adaptation mechanism, while in indirect MRAC the adjustment of the controller parameters is made in two steps. In the first step, the control law is reparametrized so that the plant parameters appear explicitly in the control law. In the second step, the controller parameters are calculated from the estimates of the plant parameters.