Finite Time Segment Sliding Mode Attitude Control Of Flexible Satellites

The attitude control of modern satellites is indispensable in the space mission.Because of the uncertain factors such as the vibration of flexible attachment,the uncertainty of the inertia matrix and the disturbance torque of space environment,the attitude controller should be designed comprehensively.Otherwise,it will be difficult for the satellite to achieve the required control accuracy when performing the space mission,and the speed of attitude control will also be affected,which may even cause the satellite attitude out of control in serious cases.Based on the model of flexible satellites expressed by quaternion and Euler axis / angle,this dissertation aims at the finite time sliding mode attitude stabilization and attitude tracking control of the flexible satellite with the inertia matrix uncertainty and external disturbance torque.In this paper,the attitude stabilization and tracking control of the flexible satellite are studied in the following aspects.A sliding mode attitude controller based on finite time stability is designed to solve the attitude stability control problem of flexible satellite system,which has the uncertainty of the inertia matrix and external disturbance.Under the condition that the flexible modal information can be measured,with the segment sliding mode control principle and Lyapunov’s finite time stability theorem,the finite time sliding mode attitude stability controller is designed by selecting the sectional sliding mode surface to realize the fast attitude stability of the flexible satellite.The effectiveness of the designed controller is verified by simulation,and compared with the equivalent sliding mode controller,it has better performance in control speed and control accuracy,and also has better suppression effect for flexible mode.Considering the fact that the modal information of flexible satellite can not be measured in practical application,a flexible modal observer is constructed to estimate the modal information values,and then a finite time sliding mode attitude stabilization controller based on the observer is designed.The estimation ability of the observer for the flexible modal information is verified by the error curve of the flexible modal information and the observed value.Compared with the flexible satellite attitude stability control,the flexible satelliteattitude tracking control problem is more complex.In view of the attitude tracking control problem of the flexible satellite system with the uncertainty of the inertia matrix and the external disturbance,a finite time sliding mode attitude tracking controller is designed,which makes up the deficiency that the exponential convergence speed of the standard sliding mode controller drops too fast,and reaches the control target that fast arrival of the desired attitude.The finite time sliding mode attitude tracking controllers are designed in the cases with measurable and unmeasurable flexible modes.Lyapunov’s finite time stability theorem is used to prove that the designed controllers can make the attitude of the system reach the desired attitude in finite time.Finally,the effectiveness and the superiority of the controllers are verified by simulation.