Quadrotor Fault Tolerant Flight Control and Aerodynamic Model Identification

As Multi-rotor Unmanned Aerial Vehicles, or drones, are gradually becoming more popular in civilian applications, the safety of these flying machines becomes a significant concern. Such drones are powered by multiple rotors to generate lift and control torques. Hence, the failure of rotors can severely threaten their flying safety. Direct consequences of rotor failures are loss-of-control and a subsequent crash if no ad-hoc flight control method can take over. Such a method, built on the principles of Fault Tolerant Control (FTC), is thus essential to improving the safety of multi-rotor drones. Fixed-pitch quadrotors are the simplest type of multi-rotor drones and have been extensively used in various applications thanks to their simplicity and higher energy efficiency. However, they suffer most from rotor failures since it requires a minimum of four fixed-pitch rotors to achieve full attitude control. Therefore, devising FTC algorithms for quadrotors presents a significant challenge. As there have been many efforts to develop FTC for quadrotors flying in nearhover conditions, a primary objective of this thesis is further expanding the capability of FTC methods to high-speed conditions where significant aerodynamic effects arise that brings large model uncertainties to the control algorithm. The high-speed flight conditions can be, for instance, the cruising phase of a quadrotor (e.g., delivery drone). Once rotor failure occurs, these aerodynamic effects can adversely impact the performance of FTC methods, and even drive the damaged quadrotor into upset conditions with abnormal attitude and angular rates. On the one hand, it is essential to improve state-of-art FTC methods withstanding significant aerodynamic effects as well as possible large initial disturbances. On the other hand, these aerodynamic effects need to be further investigated and modeled to facilitate the development of FTC in high-speed conditions. These two aspects constitute the two major parts of this thesis...