Disturbance observer-based output feedback control for uncertain QUAVs with input saturation

This paper investigates the problem of disturbance observer-based output feedback control for quadrotor unmanned aerial vehicles with external disturbances, uncertainties and input saturation. Different from the existing results, we propose a novel control algorithm towards attitude system and position system. First, considering that not all signals can be measured directly by sensors, we construct a full-order state observer to estimate the unmeasureable state variables. Second, a nonlinear disturbance observer is designed to estimate the unknown external disturbance encountered by quadrotor during flight. Then, novel second order sliding mode surfaces are proposed to design the attitude controller and position controller, which can effectively attenuate the chattering effect without sacrificing the robustness of the controller. In addition, an auxiliary system is developed to eliminate the influence caused by input saturation. Moreover, by using the Lyapunov stability theory, it is proved that the designed attitude and position controllers can ensure that all signals of the resulting closed-loop system are uniformly bounded. Finally, a simulation example is given to verify the effectiveness of proposed algorithm. (C) 2020 Elsevier B.V. All rights reserved.