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Observer-Based Super-Twisting Sliding Mode Control with Fuzzy Variable Gains and its Application to Overactuated Quadrotors

In this paper, we propose an observer-based super-twisting sliding mode control with fuzzy variable gains (OST-FVG) for general second-order nonlinear systems. First, the super-twisting observer with fuzzy variable gains is designed for state estimation, for which we show finite-time convergence of the estimation error to zero under the bounded disturbance. Then, together with the proposed observer, the sliding mode control with fuzzy variable gains is designed to ensure precise tracking control performance and to alleviate the chattering phenomenon. We apply the OSTFVG to the overactuated quadrotor modeled by the second-order nonlinear system within the quaternion framework, which resolves underactuation and singularity problems appeared in standard quadrotors. In simulation results of attitude and position control, the fuzzy mechanism implemented in the OSTFVG guarantees faster convergence of the quadrotor to the desired position and more precision tracking performance compared to the standard observer-based super-twisting sliding mode control.