Extended Disturbance Observer Combined with Nonlinear Sliding Surface for Robust Control of Mismatched System

A nonlinear sliding mode control combined with an extended disturbance observer is proposed for a class of uncertain mismatched systems. The main idea is to intentionally add a nonlinear state in the sliding surface for improved performance. The proposed scheme ensures robustness under varying mismatched uncertainty and faster convergence than linear sliding mode control. The control scheme is verified via simulation and the efficacy of control is validated on a 2-DOF flexible joint laboratory setup.