High-gain observer with higher order sliding mode for state and unknown disturbance estimations

SUMMARY In this paper, we consider the estimation problem of a class of single‐input–single‐output nonlinear Lipschitz systems with nonmatching uncertainty or disturbance, where the distribution vector may include the unknown states. A hybrid nonlinear observer structure that combines a high‐gain feedback with higher order sliding mode term is proposed. The high‐gain feedback works to constrain the estimation error to within an invariant set, and the sliding mode term will asymptotically track the uncertainty if the system satisfies strict structure assumptions. Furthermore, with the higher order sliding mode, the chattering effect will be effectively attenuated without sacrificing robustness, and the system uncertainty can be recovered without filtering effect. Copyright © 2013 John Wiley & Sons, Ltd.