Adaptive control based on special compensation methods for time-varying systems subject to bounded disturbances

Abstract

An adaptive controller based on some compensation methods that preserve stability for fast time-varying plants in the presence of bounded output disturbances and unmodelled dynamics is presented. No minimum phase assumption is required by the adaptive scheme to guarantee closed-loop stability, although the unstable plant zeros must be transmitted to the closed-loop system to avoid unstable cancellations. The unknown plant parameters are estimated by a normalized algorithm with dead zone. The design is completed with a modified control law which adds an internal impulse to the system whenever the controllability of the estimated model is lost. This strategy confers a self-excitation capability 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 special compensation methods, and global stability is ensured. The performance of the given scheme is evaluated...