Adaptive output feedback control with disturbance attenuation for a class of nonlinear systems

For a class of nonlinear single input, single output systems containing uncertain constant parameters, belonging to a known compact set, and possibly affected by unknown time-varying bounded disturbances, we address the problem of designing an adaptive output feedback control so that: i) all signals of the closed loop system are bounded; ii) when disturbances are zero asymptotic output tracking with transient specifications is achieved in spite of uncertain parameters; iii) when disturbances are present, their effect on the tracking error is arbitrarily attenuated. We redesign adaptive output feedback controls previously obtained so that unknown time-varying disturbances entering linearly in the state equations may be attenuated up to an arbitrary degree.