Fixed-time tracking control for quadrotor UAV via a novel disturbance observer

This paper is dedicated to developing a fixed-time trajectory tracking control strategy for quadrotor unmanned aerial vehicles (QUAVs), addressing the challenges posed by external disturbances and actuator faults, which are prevalent in real-world UAV operations. Initially, nominal controllers for attitude and position systems are proposed to drive tracking errors to a small region near zero in fixed time, assuming no external disturbances and no actuator faults. Subsequently, to actively compensate for the lumped disturbances often encountered during UAV missions, two novel fixed-time disturbance observers are constructed using fixed-time sliding mode surfaces and filtering techniques, enabling precise estimation of lumped disturbances. A comparative analysis reveals that the proposed disturbance observer excels over existing ones by eliminating stringent upper bound assumptions on disturbances and their derivatives, thus providing smoother and more precise estimation. Then, in combination with feedback from observers, robust fixed-time controllers are designed, and the stability is substantiated through Lyapunov theory. Ultimately, the effectiveness and superiority of the proposed controllers and disturbance observers are demonstrated through comprehensive simulations and comparative analysis, showcasing their potential to significantly enhance the performance and reliability of UAVs in various operational scenarios.