Applying sliding mode technique to design extended state observer for nonlinear systems

This paper applies sliding mode and stable pole-zero cancelation techniques to design a finite time extended state observer for a class of single-input single-output nonlinear systems in the presence of unknown uncertainties and disturbances. The proposed estimation approaches, including first-order and second-order sliding mode extended state observers, can provide more design flexibility and achieve good performance compared with the conventional extended state observers. Moreover, it has a good form for theoretical stability analysis in which the estimation errors can be converged to a neighborhood of zero while remaining uniformly bounded in finite time. The characteristics of the developed observer is presented in the frequency domain, followed by the corresponding analysis in the time domain. Finally, simulation results demonstrate the validity of the proposed method.