In-Ground-Effect Disturbance-Rejection Altitude Control for Multi-Rotor UAVs

This paper presents a robust altitude control that merges the principles of active disturbance rejection control (ADRC) with the in-ground-effect model (IGE). To this end, a nonlinear extended state observer is designed along the vertical axis, taking attitude and altitude measurements. Then, the forces generated by low-level flight, ground effect and other external disturbances are estimated and used (as an anticipation term) together with a non-linear control law (as a feedback term) to reject them. Closed-loop stability is analyzed in the Lyapunov sense. Extensive numerical simulations and real-time experiments validate the proposal. Thanks to its simplicity, the control algorithm is easy to implement. It can be used for various maneuvers that depend on proximity to the ground, obstacles or surfaces, such as take-off, landing, inspection, surveillance and hovering.