Disturbance Suppression of Gimbal Servo Motor Based on Improved ADRC and ISMC Method

In the gimbal system, there are many disturbances that will reduce the speed accuracy of the servo motor. To suppress those disturbances, this paper explores a composite method based on improved active disturbance rejection control (IADRC) method and a dynamic sliding mode surface in ISMC method, which are considered to be common control methods in the presence of external disturbances and uncertainties to improve the performance of the servo motor. IADRC has inner and outer loops, and the two extended state observers (ESO) whose parameters can be tuned independently are arranged in a cascade structure. The outer loop observer provides system state estimation to build the feedback controller, and the inner loop observer deals with the generalized disturbance. Different from the conventional cascade ESO which is focused on attenuating the measurement noise, IADRC helps to enhance the robustness of the system to parameter uncertainty. Integral sliding mode control (ISMC) is employed to reduce the steady-state error, and its dynamic sliding surface is designed to reduce the overshoot of the gimbal servo system during the step. Besides, ISMC is mainly applied to enhance the system's immunity to low-frequency disturbances, while IADRC is employed for the immunity to medium frequency disturbances. Finally, the proposed composite method is carried out on the gimbal servo system in the control moment gyro. The results of the simulation and experiments show that the method is effective, and the performance of the servo motor is significantly enhanced.