Robust super-twisting sliding mode control of input-delayed nonlinear systems using disturbance observers and predictor feedback

This paper investigates prediction-based robust super-twisting sliding mode controller design for nonlinear systems with input delay and external disturbances. A novel predictor feedback is introduced based on state predictions of the original and transformed models. To cope with the external disturbances, a set of disturbance observers are utilized which estimate the future values of disturbances asymptotically. Super-twisting sliding mode control is used to avoid chattering phenomenon which is also able to handle external disturbances. Proposed design can handle all external disturbances that their derivatives vanish at infinity. Stability proof of the closed-loop is given in details ensuring the asymptotic stability of the tracking errors and finite time vanishing of the sliding surface. To illustrate effectiveness and applicability, the proposed design is applied to a two-link robot and a serial variable stiffness actuator. Simulation results show that input delays of the robot and actuator are compensated, and external disturbances are correctly estimated and attenuated.