Disturbance Observer-Based Adaptive Neural Network Output Feedback Control for Uncertain Nonlinear Systems

This article is devoted to the output feedback control of nonlinear system subject to unknown control directions, unknown Bouc–Wen hysteresis and unknown disturbances. During the control design process, the design obstacles caused by unknown control directions and Bouc–Wen hysteresis are eliminated by introducing linear state transformation and a new coordinate transformation, which avoids using the Nussbaum function with high-frequency oscillation to deal with the issue. Besides, to settle the issue caused by the unknown disturbances, a novel nonlinear disturbance observer is designed, which has the characteristics of simple structure, low coupling, and easy implementation. Especially, a compensation item is constructed to offset the redundant items generated in the backstepping design process. Simultaneously, using the neural network and backstepping technology, an output feedback controller is devised. The controller ensures that all closed-loop signals are bounded, and the system output, state observation error, and disturbance observation error converge to a small neighborhood of the origin. Finally, to illustrate the effectiveness of the proposed scheme, simulation verification is carried out based on a numerical example and a Nomoto ship model.