This article presents an uncertainty and disturbance estimator (UDE) based global trajectory tracking control strategy for a quadrotor. The main contribution of this article is the fusion of the UDE technique with the unit quaternion to achieve the robust global full degrees of freedom trajectory tracking control with experimental demonstrations. The novelty of this article lies in the development of the UDE-based global tracking technique to the overall system (attitude and position) with a quaternion-based nonlinear reference model. The UDE-based attitude and position controllers are derived from the unit quaternion-based quadrotor dynamics with a cascade control structure to deal with underactuation, model uncertainties, and external disturbances. The attitude controllers that are developed with the backstepping techniques avoid the rotation matrix calculation and the unwinding problem. The position controllers are derived using the thrust-vectoring approach. A nonlinear unit quaternion-based reference model is developed to achieve the time-scale separation for the cascade control loops. The stability analysis of the closed-loop system is conducted with the Lyapunov method. Extensive flight experiments are conducted to demonstrate the global singularity-free tracking property and the superior robustness of the proposed controller.
- robust control
- uncertainty and disturbance estimator (UDE)
- unit quaternion