Error-constrained fixed-time trajectory tracking control for a stratospheric airship with disturbances

In this paper, a novel fixed-time trajectory tracking control method is presented for a six degrees of freedom (6-DOF) stratospheric airship with time-varying error constraints and disturbances. The tan-type barrier Lyapunov function (BLF) method is extended by the adding a power integrator technique to deal with the time-varying error constraints with the fixed-time stability guaranteed, which ensures that the convergence of a stratospheric airship to the reference trajectory can be achieved in a finite time regardless of its initial condition. Also the complex differential calculation is avoided in the backstepping design. A new fixed-time disturbance observer (DO), which counts on less prior knowledge of disturbances, is constructed to estimate the unknown disturbances. The proposed control method is developed based on the transformed error model, thus can be readily extended to a wide range of second-order mechanical systems. Finally, numerical simulations demonstrate the effectiveness of the proposed control scheme.