Disturbance Separation-Based Enhanced Antidisturbance Attitude Control for Flexible Spacecrafts With Composite Disturbances

The disturbances of flexible spacecrafts exhibit composite property, which means that they are heterogenous and inherently coupled with the attitude variables, control inputs, and even the other uncertainties. The separation and thereby compensation of the composite disturbances are crucial to the improvement of attitude control performances. By incorporating two popular disturbance rejection methods, the disturbance observer-based control and the equivalent input disturbance (EID)-based control, into one unified framework, a refined disturbance separation-based enhanced antidisturbance control law is proposed for flexible spacecrafts. In the presence of composite disturbances including recessive flexible vibration, additive actuator error, and multiplicative inertia uncertainty, a deep-coupled attitude control model is established. On this basis, a disturbance separability condition and a refined disturbance separation method are proposed. More specifically, the recessive flexible vibration is estimated by a refined disturbance observer (RDO), while the estimation error of RDO and the other disturbances (e.g., additive actuator error) are estimated by the EID estimator. The multiplicative inertia uncertainty is attenuated by the feedback control. Finally, numerical simulations and experimental results are, respectively, given to demonstrate the effectiveness of the proposed method.