Global tracking for a class of nonlinear systems subject to unknown sinusoidal disturbances

The widely studied class of minimum phase observable nonlinear systems with output dependent nonlinearities is considered. The problem of tracking any smooth bounded output reference signal is addressed, when the system is perturbed by additive disturbances generated by an unknown stable linear exosystem whose order is known. An output feedback solution is presented which achieves asymptotic tracking for any initial condition of the closed loop system and of the exosystem, without requiring any persistency of excitation condition.