High-Precision Anti-Disturbance Gimbal Servo Control for Control Moment Gyroscopes via an Extended Harmonic Disturbance Observer

In control moment gyroscopes (CMGs), the gimbal is expected to rotate at a low speed with high precision so that high-precision gyroscopic torque can be generated to realize high-precision spacecraft attitude control. However, there are complex and multiple disturbances in the gimbal servo systems, which may deteriorate the gimbal control performance to a great extent. In this paper, an extended harmonic disturbance observer (EHDO)-based composite controller is proposed to reject the effects of multiple disturbances on the control performance of gimbal servo systems. Firstly, an EHDO is developed for an mth-order model describing disturbance dynamics in which the rotor dynamic imbalance torque along gimbal axis is modeled as a harmonic, and the others are approximated as a polynomial. Compared with conventional extended disturbance observers, EHDO can estimate multiple disturbances with high precision even with a lower bandwidth. Secondly, a backstepping-based composite controller is designed to achieve high-performance gimbal control for CMGs. Finally, simulation and experimental results are presented to demonstrate the effectiveness of the proposed method.