Sigmoid Super-Twisting Extended State Observer and Sliding Mode Controller for Quadrotor UAV Attitude System With Unknown Disturbance

The super-twisting algorithm has been verified its effectiveness in attitude control for quadrotor with unknown disturbance. However, the discontinuous signum function in super-twisting formulation causes the unwanted chattering problem and thus affects the attitude control performance. In this paper, we replace the signum function with sigmoid function and propose the sigmoid super-twisting extended state observer (SSTESO) and sliding mode controller (SSTSMC). Besides, a rigorous convergence analysis of proposed nonlinear error system based on the Lyapunov stability theory is performed, and the parameter selection rule is given. Numerical simulations are implemented in presence of manually designed disturbance in order to verify the advantage of the proposed algorithm compared with original super-twisting algorithm. Results show that the introduction of sigmoid function can not only reduce the chattering effect, but also maintain the advantage of supertwisting algorithm.