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Nonlinear output feedback tracking with almost disturbance decoupling. (English) Zbl 0967.93042
For a class of uncertain nonlinear SISO systems, output feedback control algorithms are proposed, which globally solve the tracking problem with almost disturbance decoupling. Systems belonging to the considered class are globally transformable into observable, minimum-phase systems, whose nonlinearities depend on the output only; the dynamics of these systems may be affected by unknown time-varying disturbances or parameter variations entering linearly in the state equations. If $\rho$ denotes the relative degree of the given system, the resulting controller is static when $\rho =1$ and dynamic of order $\rho -1$ when $\rho >1$. It is shown that, for any smooth bounded reference signal with bounded time derivatives up to order $\rho$, the influence of the disturbances on both ${L}_{2}$ and ${L}_{\infty }$ norms of the output tracking error is arbitrarily attenuated by increasing a positive scalar control parameter. In the particular case when the disturbances are zero, the equilibrium point of the closed-loop system corresponding to the reference signal is globally asymptotically stable and the output exponentially tracks the reference signal.
##### MSC:
 93B52 Feedback control 93C73 Perturbations in control systems 93D15 Stabilization of systems by feedback 93C10 Nonlinear control systems