Research On Robust Control Methods For Spacecraft Attitude

For rigid spacecraft or flexible spacecraft with flexible appendages,many uncertainties or disturbances exist in the attitude maneuvering process.The present generation of spacecraft should be capable of high-precision pointing and better robustness to external disturbances and various uncertainties.The objective of this dissertation is that considering several restrictive problems,e.g.external disturbances,model parameter uncertainties,controllers gain perturbations,input delay,measurement errors,input constraints or saturation,actuator fault signals,effective attitude controllers should be developed to ensure accurate and rapid response to various attitude maneuvering commands.The main contents of this dissertation include the following parts:A non-fragile output feedback control method is proposed for rigid spacecraft considering model parameter uncertainties,controller gain perturbations and input saturation.First,the condition of input constraints is given.Then two controllers are designed in terms of additive and multiplicative perturbations,and the system stability under the corresponding controller is proved.Simulation results show that compared with the standard output feedback controller,the proposed non-fragile output feedback controller can significantly improve the steady-state accuracy of attitude angle,and greatly reduce the total energy consumption.Subsequently,considering input delay,an intermediate state observer-based controller is proposed,which can guarantee the uniform ulimate boundedness of the system and can estimate the attitude information and fault information simultaneously.Simulation results show that compared with the prediction-based sampled-data H∞ controller,the proposed intermediate state observerbased controller can significantly improve the steady-state accuracy of attitude angle and angular velocity,and greatly reduce the total energy consumption.A fault-tolerant non-fragile control method is proposed for rigid spacecraft considering model parameter uncertainties,controller gain perturbations,measurement errors,actuator faults and input saturation.First,a random intermediate variable is introduced,and its expectation-based intermediate state observer is designed to obtain a new closed-loop system.Then non-fragile controllers are designed in terms of additive and multiplicative perturbations,and the stability analysis is given.Simulation results illustrate the superior performance of the proposed controller compared with the state feedback controller in terms of energy consumption reduction.A state feedback H∞ control method is proposed for flexible spacecraft considering model parameter uncertainties,controller gain perturbations,measurement errors and input magnitude constraint.First,the active and passive vibration suppression schemes are integrated into attitude dynamics model with a similar form.Then the non-fragile controllers are designed in terms of additive and multiplicative perturbations,and the input magnitude constraint is explicitly considered.Simulation results show that compared with the input shaping-based active vibration suppression method,the state feedback H∞ controller has better vibration suppression effect and lower total energy consumption.Subsequently,an intermediate state observer-based H∞ controller is designed to achieve attitude stabilization and vibration suppression without prior information on attitude,modal displacement and inertia matrix of flexible spacecraft,and the input magnitude and rate constraints are explicitly considered.Simulation results show that compared with the mixed H2/H∞ controller,the proposed controller can significantly reduce system settling time and vibration suppression time.