Fixed-time observer-based adaptive free-will arbitrary time intelligent fault-tolerant control for an autonomous quadrotor

This article presents an adaptive fault-tolerant control (FTC) strategy based on a fixed-time fault observer for the attitude, altitude tracking, and control of quadrotor unmanned aerial vehicles (UAVs), effectively addressing actuator faults, model uncertainties, and unknown disturbances. The fixed-time sliding mode observer (FTSMO) is implemented to estimate the actuator fault and ensure the estimation error convergence in the fixed time. Subsequently, an adaptive free-will arbitrary time terminal sliding mode control is designed for prescribed-time convergence of the system states and handles the actuator faults simultaneously. The sliding surface of the proposed control design utilises the concept of free-will arbitrary time stabilisation, ensuring prescribed-time convergence of the system states irrespective of initial conditions. The existence of model uncertainty and unknown disturbances is compensated by implementing a radial basis function neural network (RBFNN) along with secondary adaptive law without requiring prior knowledge of the uncertainty and disturbances. The stability analysis of the closed-loop dynamics is established by utilising the Lyapunov method. Finally, a comparative numerical simulation is conducted to validate the superiority of the proposed fault-tolerant control scheme in comparison to the existing prescribed time control and FTC design methods.