Output feedback control for uncertain nonlinear systems with unknown gain sign

In this paper, adaptive output feedback control based on K-filters and dynamics surface control is designed for a class of nonlinear systems with unknown gain sign and unmodeled dynamics as well as dynamic uncertainties. Nussbaum function is used to deal with unknown gain sign and neural networks are used to approximate the unknown continuous function of the system. By the novel description to unmodeled dynamics, the dynamic signal used to handle the unmodeled dynamics in the existing literature was avoided. The assumption condition with respect to the dynamic uncertain terms is relaxed. The processes of the unknown continuous functions produced in stability analyses are simplified, and the extra term caused by the introduction of Nussbaum function is effectively solved. It is shown that all the signals in the closed-loop control system are semi-globally uniformly ultimately bounded. Simulation results are presented to illustrate the effectiveness of the proposed approach.