Attitude Control And Vibration Suppression Of Large Scale Flexible Satellites

Attitude control of satellite refers to the technology of gaining and maintaining the orientations of satellites in space, i.e. gaining and maintaining the attitudes of satellites relative to certain coordinates. During the mission of satellites, their attitudes are supposed to meet certain requirements, such as pointing to the earth, stars or any other targets. And sometimes their attitudes are required to change according to commands. Due to environmental disturbance, attitudes of satellites may drift away, so it is necessary to stabilize and control the attitude accordingly. As the Proportional Derivative (PD) controller which is widely used in engineering has difficulties to control the attitude to high precision, advance controllers, such as Linear Quadratic (LQ) controller, H∞controller and Terminal Controller, are designed and tested to see whether they can precisely control the attitude. One or more groups of matrix differential equations need to be solved to design the above mentioned advanced controllers. This thesis introduces Generating Functions to solve this problems and the equivalence between the solutions by Generating Function and the traditional Riccati transformation methods is proved theoretically, which allows recently developed algorithms based on Generating Functions to be used. Simulation results of the above controllers show that, compared with PD controller, the presented controllers greatly increase the accuracy and reduce the stabilization time.As technology develops, the structures of the satellites are becoming larger and more complex, which makes it necessary to consider the flexibility, i.e. takes the vibration and its influence to the satellites into account. Some structures like the antennae need to have their vibrations controlled to ensure precise pointing. So the active vibration control or vibration suppression of flexible satellites is in need. This thesis discusses the attitude control and vibration suppression of flexible satellites. Firstly, adaptive output feedback controller is applied and the simulation results of a satellite show that the attitude can be well controlled while the vibration take too much time to stabilize and even unable to stabilize. Secondly, piezoelectric material is introduced as actuator to control the vibration and Positive Position Feedback (PPF) controller is applied to design the control law. It shows that vibration of a beam is suppressed using this method. Finally, we combine the two controllers to control the satellite with a reasonable way and it turns out that the compound controller can control the attitude and suppress the vibration also.