ADAPTIVE-CONTROL BASED ON SPECIAL COMPENSATION METHODS FOR TIME-VARYING SYSTEMS SUBJECT TO BOUNDED DISTURBANCES

An adaptive controller based on some compensation methods that preserv e stability for fast time-varying plants in the presence of bounded ou tput disturbances and unmodelled dynamics is presented. No minimum pha se assumption is required by the adaptive scheme to guarantee closed-l oop stability, although the unstable plant zeros must be transmitted t o the closed-loop system to avoid unstable cancellations. The unknown plant parameters are estimated by a normalized algorithm with dead zon e. The design is completed with a modified control law which adds an i nternal impulse to the system whenever the controllability of the esti mated model is lost. This strategy confers a self-excitation capabilit y to the system, so that it makes unnecessary the presence of external persistently exciting signals. As a result, the estimated models are sufficiently controllable by the underlying control law based on the s pecial compensation methods, and global stability is ensured. The perf ormance of the given scheme is evaluated by simulations.