Stable hovering of proximity quadrotor UAV in-ground effect via model compensation controller

This paper addresses the challenge of achieving stable hovering of two proximate Quadrotor UAVs (QUAVs) under the influence of ground effect, which introduces complex rotor airflow interactions. The existing rotor in-ground effect (IGE) models fail to accurately capture the ground effect on QUAVs, particularly when dealing with the interaction between proximate vehicles. To overcome this limitation, a compensation function observer (CFO) is proposed to estimate the unknown forces and moments induced by the ground effect. Subsequently, a CFO-based model compensation controller (MCC) is developed to ensure stable hovering near the ground. The convergence of the CFO and the stability of the closed-loop system are rigorously established using the Lyapunov method. To validate the effectiveness of the proposed approach, comprehensive experiments are conducted on an experimental platform equipped with an indoor optical positioning system and two QUAVs with a fixed axis distance of 450 mm. The experiments involve single QUAV stable hovering at various altitudes, as well as stable hovering of two proximate QUAVs. Based on the experimental data estimated by the CFO, a quadrotor IGE model is developed, and parameters are identified, and it appears an exponential convergence trend with unimodal oscillation because of the phenomenon of thrust loss. Extensive experimental comparisons are also performed to analyze the superiority of the proposed MCC algorithm in scenarios involving both ground effect and proximity.