Robust Output Regulation of a Class of Nonlinear Systems Via Disturbance Observer in the Presence of Matched and Unmatched Uncertainties

The purpose of this paper is to propose a controller for nonlinear systems to achieve robust asymptotic tracking of a class of reference signals, in the presence of matched and unmatched disturbances and model uncertainties. The disturbances and reference signals are generated using two linear exosystems. In the proposed controller, instead of using the upper bound of disturbances in the design process, their instantaneous values are estimated disturbance observer. Therefore, disturbance observer-based control (DOBC) methods are less conservative with respect to conventional approaches. In addition to the DOBC design, a new stepwise procedure based on backstepping technique and sliding mode control is proposed. In the proposed approach, in each step, estimations of disturbances and the upper bound of model uncertainties are used to compose virtual control laws; these virtual control laws compose the final control law. Finally, numerical and practical examples are simulated to show the efficiency of the proposed technique and also to verify the theoretical results.