PSO-Nonsingular Fast Terminal Sliding Mode Control for Hexarotor in Turbulent Atmospheric Boundary Layer With Disturbance Observer

Hexacopter operations in the atmospheric boundary layer (ABL) are affected by gusty winds and turbulence, leading to collision risks or crashes. Stability of the hexacopter UAV in gusty winds is challenging in urban space. In this paper, non-singular fast terminal sliding mode control (NFTSMC) is optimized using particle swarm optimization for altitude and attitude control of a hexacopter UAV in turbulent wind conditions. The nonlinear disturbance observer is designed to estimate and compensate for the external perturbations in ABL, such as wind gusts, using the Dryden turbulence model. The presented control law demonstrates superior trajectory tracking of the translational axis (x,y,z$$ x,y,z $$) and rotational components (phi$$ \phi $$, theta$$ \theta $$, psi$$ \psi $$) while ensuring singularity-free convergence, reduced chattering, and smooth actuation in turbulent wind conditions. Lyapunov-based stability analysis proves global asymptotic convergence, guaranteeing robustness against unmodeled dynamics and urban wind disturbances.