Fractional-order sliding mode position tracking control for servo system with disturbance

In this paper, the issue of position tracking control of servo system with external disturbance is studied. A novel fractional-order sliding mode control (FOSMC) strategy is proposed. To be specific, firstly, the motor parameter drift, additional unknown disturbance and the uncertainty of load torque are considered as lumped disturbance, and a nonlinear disturbance observer (NDO) is designed to estimate the disturbance. Secondly, fractional-order terminal sliding mode surfaces (FOTSMS) are designed for the current loop and the position-velocity loop, respectively, as well as the FOSMC is presented based on NDO, in which FOSMC of position-velocity loop introduces second-order super-twisting term to reduce the chattering of the system. Furthermore, the stability of the FOSMC is analyzed. Finally, the effectiveness of the proposed algorithm is verified by simulations and experiments.