Sliding mode control with nonlinear disturbance observer for a class of underactuated system

In this study, a sliding mode controller based on nonlinear disturbance observer is investigated to control a class of underactuated system which is in cascaded form. By using strict feedback, the underactuated system is presented as a special cascade normal form convenient for controller design. A sliding mode controller is designed to stabilize underacturated plant directly and drive the variables to the sliding surface. In order to improve performance and robustness, a nonlinear disturbance observer was designed to compensate for external disturbances and model uncertainties. The theoretical results are illustrated by simulations on the acrobot. The simulation results show that the sliding mode controller with nonlinear disturbance observer can suppress the disturbance effectively.