Uncertainty and disturbance estimator-based geometry tracking control for quadrotors without linear velocity measurements

This paper addresses the trajectory tracking control problem of a quadrotor under uncertain model parameters, external disturbances, and unmeasurable linear velocity. The main contribution of this paper is to present a geometric control strategy with a simple structure and easily adjustable parameters, which combines the differentiator and uncertainty and disturbance estimator techniques to achieve global trajectory tracking control. First, a cascade control framework is introduced to solve the strong coupling and underactuated problems of quadrotors. Furthermore, an antidisturbance outer-loop differentiator-based position controller is designed based on the uncertainty and disturbance estimators (UDE) to achieve accurate quadrotor tracking of the desired trajectory. The higher order control inputs of the translational dynamics are estimated using a differentiator to determine the desired angular velocity and its derivative. Then, a robust inner-loop geometric controller is derived in Lie algebraic space using the rotation matrix. After that, the stability analysis of the closed-loop system is executed using the Lyapunov stability theory. Finally, the numerical simulation verifies that the method enables the quadrotor to have strong robustness and excellent tracking capability in the presence of large initial angles, time-varying disturbances, and unmeasured linear velocity.