Disturbance observer-based singularity-free trajectory tracking control of uncertain quadrotors with input saturation

This paper presents a robust nonlinear controller based on disturbance observer for a quadrotor with input saturation and modeling uncertainties. The controller is designed with the hierarchial inner-outer loop structure. The position controller is constructed with the saturation function to achieve the nonsingular and bounded trajectory tracking. The speed of motor can work in a reasonable range without saturation by appropriate parameters selections criteria of controller magnitude. The attitude loop controller is designed based on the attitude representation of unit-quaternion and backstepping technique to achieve the attitude tracking. The second-order disturbance observers are employed to estimate and compensate the input saturation and unmodeled dynamics. Simulation results are illustrate the effectiveness of the proposed control algorithm.