Active anti-disturbance control of a quadrotor unmanned aerial vehicle using the command-filtering backstepping approach

In this paper, a backstepping-based nonlinear controller is developed to control the quadrotor in the presence of constant and time-varying disturbances. The control law is derived based on Lyapunov stability arguments. The controller is integrated with a disturbance observer to estimate and attenuate the effect of the disturbing forces and moments influencing the quadrotor. In this approach, no disturbance model is required for the disturbance observer. Discontinuous terms are added to the control law to ensure the negative definiteness of the Lyapunov function derivative without neglecting the disturbance observer estimation errors. Command filtering is used to compute the derivatives of the virtual control signals to avoid the complex analytic derivation of these derivatives, and to avoid differentiating the discontinuous terms existing in the controller. The effectiveness of the developed controller is investigated in simulations against disturbances due to partial actuator failure, wind, and unmodeled rotor dynamics.