Adaptive recursive nonsingular fast terminal sliding mode control for tracker design of quadrotor with unknown disturbances

In the face of parametric uncertainties and external disturbances, a recursive nonsingular fast terminal sliding mode controller (RNFTSMC) based on adaptive laws is presented for the attitude and altitude of a quadrotor. The first step is to implement recursive sliding mode control, which includes a two-layer sliding surface, an integral sliding manifold, and a fast nonsingular terminal sliding manifold. In turn, both sliding manifolds converge to zero in finite time without any singularity in the structure of the proposed controller. The initial value of the integral sliding manifold is set to eliminate the reaching phase. The upper bound of the unknown disturbances is addressed by estimating it using the adaptive adjustment technique. It is shown that the altitude/attitude control system converges in finite-time and that the tracking errors converge to zero. Finally, a numerical simulation is carried out for a quadrotor in the presence of disturbances. The simulation results illustrate the control performance that is predicted.