Active finite-time disturbance rejection control for attitude tracking of quad-rotor under input saturation

For the attitude tracking of quad-rotor system in the presence of disturbances and input saturation, an active finite-time disturbance rejection control method is presented in this paper. Specifically, first, based on a second-order attitude model of quad-rotor in the absence of disturbances, a bounded finite-time attitude control algorithm under input saturation is proposed to conquer the saturation constraint for practice system. At the second step, considering the existence of disturbances including constant disturbances or time-varying disturbances, a finite-time disturbance observer is designed to estimate the disturbances. Finally, using the idea of active disturbance rejection, the disturbance is directly compensated through the control input channel in the case of constant disturbance. In the case of time-varying disturbance, an integral sliding mode control method is employed here to handle the disturbance estimating error. Rigorous theoretical analysis is provided to prove that the desired attitude can be tracked in a finite time no matter what kinds of disturbances. Simulation results are given to verify the effectiveness and advantages of the the proposed active finite-time control method.