Ground effects compensation for an unmanned aerial vehicle via nonlinear disturbance observer

Abstract

In this paper，a novel nonlinear control strategy based on the nonlinear disturbance observer is developed to compensate the unknown ground effects during the landing procedure. Owing to the intricacy of the ground effects，it is very hard to obtain the precise dynamic model for the UAV's landing procedure. To solve this issue，a nonlinear observer is designed to estimate the unknown disturbance introduced by the ground effects. Then the fast terminal sliding mode control method is combined with the disturbance observer to formulate a new nonlinear robust landing control strategy which is able to suppress the unknown ground effects and drive the quadrotor to its desired landing point accurately. The Lyapunov based stability analysis is employed to prove the stability of the closed loop system，and the finite-time convergence of the UAV's altitude control error together with the disturbance estimation errors are guaranteed. Real-time flight experimental results are presented to show the good landing control performance of the proposed control strategy.