A Study Of Robust Control Method Of Large Radio Telescope Servo System

Large radio telescope has a very important role in deep space exploration, which has been widely used. The development of deep space exploration makes the detection band and pointing accuracy of the large radio telescope is becoming higher and higher, so that the diameter of radio telescope is becoming larger and larger. But with the increase of the radio telescope diameter, the structure flexibility enhances and the fundamental frequency is lower. Once the structure is affected by external excitation, the antenna structure will generate oscillation, so that the tracking accuracy and pointing accuracy is reduced. In addition, the antenna is affected by wind disturbance when it is in normal operation, and the stability and pointing accuracy of the antenna is reduced when the disturbances exists. Therefore, in the antenna servo control algorithm design, it is of great importance to suppress the flexible vibration of antenna structure and to make the control system robust.The research of this thesis is based on the large radio telescope,to design the antenna servo control algorithm. First, build the approximate dynamics model of the large radio telescope, solve the output of the model and analysis the flexible output that influence the antenna output. In addition to the influence of the flexible vibration of the antenna structure, the theoretical model we build often has uncertainty, which will affect the stability and performance of the control system. In order to design antenna servo control system in the presence of flexibility and model uncertainty, the thesis designs the LQG + H-infinity compound control algorithm, which is based on the flexible vibration suppression ability of LQG controllers and robustness of the H-infinity controllers. So that the controller can suppress the vibration of flexible structure and ensure the robustness of the system. The validity of the control method is verified by simulation.Finally, in view of the robust control problem with an existence of wind disturbance and model uncertainty, we design a compound control method based on the robust Bode plot. According to the criteria of stability robustness and performance robustness, the open-loop Bode plot can be divided into the feasible zone satisfying robustness and the forbidden zone not satisfying robustness. A controller is designed to adjust the system Bode plot to the feasible zone, which guarantees the system can keep stability robustness and performance robustness under the impact of disturbance and model uncertainty. Through a simulation experiment on a flexible system, the effectiveness of the control method based on robust Bode plot is verified.