Dynamics modeling and low rate control of gimbal servo system for single gimbal control moment gyro

In order to ensure the high precision of output torque, the precise dynamics modeling and control of gimbal servo system were studied. By thorough dynamics analysis of single gimbal control moment gyro (SGCMG) mounted on the spacecraft, the dynamic model of gimbal servo system was established, taking into account the largest disturbing torque along the gimbal axis resulted from rotor imbalance and the friction torque. For the gimbal servo system using a sinusoidal permanent magnetic synchronous motor (PMSM), the inner and outer loop controllers were both designed based on the active disturbance rejection control (ADRC) theory. The simulation results demonstrate that under the assumption that the high-frequency disturbing torque resulted from rotor imbalance is ignored, the modeled and unmodeled disturbance existing in both loops were estimated and compensated exactly using the ADRC controller, so that the high precision control of gimbal servo system was ensured. The results also show the effect level of the rotor imbalance on gimbal control precision.