IJCAS

The main contribution of this paper is to present a general design method of new nonlinear disturbance observer (NDO) based on tracking differentiator (TD) for uncertain dynamic system. The stability and convergence of the proposed NDO can be guaranteed by TD. This new NDO can be used to estimate many types of uncertain disturbances, and can overcome the disadvantages of existing NDOs that need the priori information concerning the upper and lower bounds of the disturbance and its ith derivative’s Lipschitz upper bound. It can be also applied in uncertain dynamic system for various purposes such as disturbance estimate and compensation, solving the problem of control input constraint, and reducing even eliminating chattering of control input. Simulation results are presented to show the effectiveness of the developed NDO.

Keywords: Chattering, control input constraint, disturbance estimate, nonlinear disturbance observer, tracking differentiator, uncertain disturbances, uncertain dynamic system.