Cascade Disturbance Estimator for Disturbance Suppression in Spacecraft with Flywheels

In the spacecraft with flywheels, there are multiplesource disturbances from flywheels, flexible appendages, and external space environment. Complex disturbances can degrade the attitude control performance of spacecraft and are usually suppressed by using disturbance estimation and feedforward compensation. However, flywheel rotor dynamic imbalance disturbance is difficult to suppress since it exhibits both time-varying frequency and amplitude characteristics. In this paper, a cascade disturbance estimator is proposed to estimate all disturbances. Firstly, a gradient estimator constructs novel basis functions to describe the flywheel rotor dynamic imbalance disturbance. Thus, it can accurately estimate this dynamic imbalance disturbance based on precise model information. Secondly, an extended disturbance observer is designed to further estimate residual disturbances with unknown model information to improve robustness. The proposed estimator can precisely estimate the total disturbances with a limited bandwidth. Afterwards, a composite controller based on the proposed estimator is designed to achieve high-performance spacecraft attitude control. The simulation results demonstrate the effectiveness of the proposed method.