Research On Finite Time Attitude Control Of Large Scale Rigid-flexible Coupling Satellites

Flexible satellites constituted of a central rigid body, a uniform cantilever as the flexible appendage and a tip mass experience serious coupling effect between the deformation of flexible body and large scope spatial movement, because of the existence of flexible appendages. This coupling effect is even worse when flexible satellites are in fast maneuver mode. As a result, flexible satellites are facing more challenges in dynamics modeling and attitude control compared with rigid satellites. First, Large scale flexible appendages such as solar panels and robotic manipulators are easy to be triggered into low order vibrating when flexible satellites are instable or the attitude regulation time is too long. Second, the vibration of the flexible appendages will in return degrade the attitude control accuracy. So it is important to have a deep study of the finite time control for flexible satellites. In the context stated above, finite time control for large scale flexible satellites is studied in both theory and simulation in this dissertation. The main content of this dissertation is stated below.Based on the first order approximation coupling method, the first order approximation rigid flexible coupling dynamics model of the flexible satellite is established using the Hamilton’s principle and finite elements method. This model incorporates the foreshortening term of longitudinal displacement caused by the transverse displacement of the flexible beam, which reveals the nonlinear strain-displacement relations. In addition, considering the complexity of the control design of the flexible satellite, a modification is made to simplify the first order approximation rigid flexible coupling model without influencing the control results.Based on the first order approximation rigid flexible coupling dynamics model, a nonsingular fast terminal sliding mode controller(NFTSMC) is designed in the presence of the model uncertainties and disturbances. This controller can provide finite time convergence to the equilibrium quickly with no singularities. Then a modified NFTSM output feedback controller is proposed in the condition that all the flexible vibration measurements are not available, and the finite time output feedback control is based on angle and angular velocity only. Given the situation that the angular velocity sensors have faults that the angular velocity measurements are unavailable, a terminal sliding mode observer is designed to reconstruct the angular velocity in finite time which make the NFTSMC maintain the finite time stability in the absence of the angular velocity.Considering the chattering in most of sliding mode controllers including terminal sliding mode controllers, and the low order vibration of flexible appendages triggered by the chattering, an extended state observer(ESO) is designed to decrease the control gain by estimating and compensating the total disturbance of the system incorporating flexible coupling terms. Then with the compensation effect of the ESO, a continuous terminal sliding mode controller is proposed based on the fast power reaching rule method which is proved to be a second order sliding mode in advance. The finite time stability, the elimination of chattering and the decreasing of vibration of appendages are proved both theoretically and practically.Considering the situation when some of the actuators fail to operate, an approximation of the total uncertainties including the estimated error of the faulty actuator is made using Legendre polynomial based neural network(LeNN), then combined with the NFTSMC in Chapter 3, a finite time attitude fault tolerant controller(FFTC)is designed. In order to guarantee that the output of the LeNN stays inside the bound of the estimated total uncertainties, a switch mechanism is introduced to generate a switching between the proposed FFTC and the robust controller. The proposed FFTC is shown to have the finite time stability through theoretical analysis and simulations, meanwhile the better representation capability of the LeNN, whose basic functions are implemented using only the desired attitude, make the controller design simple and efficient。...