Output-Feedback Generalization of Variable Gain Super-Twisting Sliding Mode Control via Global HOSM Differentiators

In this paper, an output-feedback version of the Variable Gain Super-Twisting Sliding Mode Control is proposed for uncertain plants with arbitrary relative degree. This extension is achieved by using global HOSM (higher-order sliding modes) differentiators with dynamic gains. Norm observers for the unmeasured state are employed to dominate the disturbances as well as to adapt the gains of the proposed differentiator, since the disturbances may be state-dependent and time-varying. The proposed control scheme guarantees global stability with robust exact tracking. As the control signal is continuous the proposed scheme alleviates the chattering phenomenon. Numerical simulations illustrate the theoretical results.