Modeling and Adaptive Nonlinear Disturbance Observer for Closed-Loop Control of In-Ground-Effects on Multi-Rotor UAVs

This paper focuses on modeling and nonlinear control of in-ground-effect (IGE) on multi-rotor aerial vehicles such as quadrotor helicopters (quadcopters). As the vehicle flies and hovers near obstacles such as the ground, walls, and other features, the IGE which is a function of the distance between the rotor and the obstacle induces a thrust that drastically affects flight behavior. This effect on each rotor can be vastly different as the vehicle’s attitude varies. Furthermore, IGE limits the ability for precision flight control, navigation, and landing in tight and confined spaces. A nonlinear model is proposed to predict the IGE for each rotor. To compensate for the IGE, an adaptive nonlinear disturbance observer (ANDO) is designed to enhance closed-loop PID control. The observer and controller are implemented in a simulation framework, where results show significant improvement in performance compared to the case without observing and compensating for the IGE. In particular, it is shown that the ANDO PID closed-loop controller improves the settling time by approximately 60%.