A robust controller for multi rotor UAVs

Unmanned aerial vehicles (UAVs) are safety-critical systems that often need to fly near buildings and over people under adverse wind conditions and hence require high manoeuvrability, accuracy, fast response abilities to ensure safety. Under extreme conditions, the dynamics of these systems are strongly nonlinear and are exposed to disturbances, which need a robust controller to keep the UAV and its environment safe. In this paper a novel robust nonlinear multi-rotor controller is introduced based on essential modifications of standard dynamic inversion control, which makes it insensitive to payload changes and also to large wind gusts. First a robust attitude controller is established, followed by lateral and vertical position control in a customary outer loop. The controllers take into account thrust limitations of the aircraft and theoretical proof is provided for robust performance. The control scheme is illustrated in simulation with a realistic nonlinear dynamical model of an aircraft that includes rotor dynamics and their speed limitations to show robustness. Lyapunov stability methods are used to prove the stability of the robust control system.