Active disturbance rejection adaptive control for uncertain nonlinear systems with unknown time-varying dead-zone input

This paper rigorously investigates the problem of active disturbance rejection control for nonlinear systems subject to uncertainties and dead-zone input. One of the features of the considered systems is that the dead-zone parameters are allowed to be time varying and asymmetrical. The main idea of this paper is to utilize an extended state observer (ESO) to estimate all the external disturbance, the uncertain nonlinearity, the unknown dead-zone model, and the unmeasurable states. A switched dynamic parameter estimation law is established to separate the dead-zone model from the total uncertainty and estimate the parameters of dead-zone online. Based on the proposed estimation law and the ESO, an output feedback linearization control law is designed to cancel the total disturbance and compensate the dead zone. The theoretical analysis of stability shows that the closed-loop system has multi-time scale convergence properties. Finally, simulation results are provided to illustrate the efficiency of the proposed method.