A novel implementation of an uncertain dead-zone-input-equipped extended state observer and sign estimator

Abstract

This paper presents a novel implementation based on the observer and estimator for a class of nonlinear systems subject to remarkable control gain variation in the presence of the dead-zone actuator. Specifically, an approximation function of the dead-zone nonlinearity is developed to overcome the non-differentiable problem so that an extended state observer (ESO) can estimate the uncertain dead-zone input. Then, a sign-projected gradient-based estimator is applied to identify the control gain and disturbances for separate compensation. In addition, the output error is decoupled from the estimation error, and the finite-gain stability with exponential and ultimate boundedness is obtained through a defined input–output mapping. Finally, comprehensive comparisons with existing methods on a brushless DC motor illustrate the strong performance and robustness of the proposed design.