Fault-tolerant adaptive fractional order sliding mode control for a quadrotor using disturbance observer

An adaptive fractional-order sliding mode control method using a disturbance observer is proposed for position tracking of a quadrotor. The mathematical model of the quadrotor considering disturbance is derived using the Euler-Lagrange equations. The model is divided into two fully actuated and underactuated subsystems. The proposed controller as the result of combining fractional calculus and the sliding mode method is designed for both subsystems separately. Furthermore, a disturbance observer is designed which deals with actuator fault, uncertainty, and wind disturbance. The stability of the closed-loop system is proved using Lyapunov theory and finite-time convergence of the variables to the desired values is guaranteed. In the numerical simulation, position tracking despite the actuator faults and effects of load and wind disturbance are investigated. Finally, the simulation results validate the superior performance and robustness of the proposed controller against actuator fault and wind disturbance and the results of controllers are compared.