Safety Flight Envelope Calculation and Protection Control of UAV Based on Disturbance Observer

In this paper, an attainable-equilibrium-set-based safety flight envelope (SFE) calculation method and a prescribed-performance-control-based SFE protection scheme are proposed for the attitude dynamic of a unmanned air vehicle (UAV) in the presence of external disturbances. To estimate the unknown external disturbances and their derivatives, a higher order disturbance observer (HODO) is developed. The definition and calculation of the SFE based on attainable equilibrium set (AES) under disturbances are studied. A safety desired trajectory based on the time-varying safety margin function and the first-order filter is developed to ensure the flight safety of UAV. A SFE protection controller is proposed based on the safety desired trajectory, backstepping method, HODO, and prescribed performance (PP) control technique. The stability of the closed-loop system is proved by the Lyapunov function method and the effectiveness of the SFE protection control law is verified by simulation.