Robust Non-fragile Attitude Control For Agile Satellites With Input Constraint

Agile satellites are able to achieve rapid attitude maneuver, and their attitude control is important guarantee for aerospace missions. Therefore, many scholars have invested considerable time and effort to study related issues, and achieved fruitful research results. However, agile satellites typically operate in the presence of various disturbances, thus many uncertain factors such as external interference moment, model parameters uncertainties and controller gain perturbations will affect satellite performance, and even lead to a satellite failure. For traditional control methods often have a high degree of fragility because of controller gain perturbations, there are some limitations in the development of space technology. To solve these problems, this dissertation has deeply researched the robust and non-fragile control problems of attitude control system of agile satellites. The main contents include the following aspects:For satellite attitude control system without considering model parameters uncertainties and controller gain perturbations, the mixed H2/H∞ control methods based on traditional LMI and extended LMI approach are proposed. Considering external disturbances, H2 performance and H∞ performance of the system, the two methods based on traditional LMI and extended LMI are designed according to the equivalence restriction of the two Lyapunov variables involving H2 performance and H∞ performance. Simulations are done to demonstrate the effectiveness of the two controllers and their performance is analyzed comparatively, which shows that the mixed H2/H∞ control method based on extended LMI makes the satellite have better agility, but it does not have the robustness of model parameters uncertainties.For satellite attitude control system considering model parameters uncertainties and controller gain perturbations, the design methods of state feedback robust non-fragile controllers corresponding to additive perturbation and multiplicative perturbation are proposed. Considering the factors such as H∞ performance, control input constraint, quadratic stability, model parameters uncertainties and controller gain perturbations and so on, the state feedback non-fragile control method of satellite attitude control system under multi-objective constraint is researched. Simulation results are compared with that of the mixed H2/H∞ control methods based on traditional LMI and extended LMI approach under conditions of controller gain perturbations, which shows that the proposed state feedback robust non-fragile controllers are still effective and feasible. However, the mixed H2/H∞ controller based on traditional LMI is very fragile, and that based on extended LMI has certain non-fragility with higher requirement for actuator.For satellite attitude control system considering model parameters uncertainties and controller gain perturbations, the design methods of output feedback robust non-fragile controllers corresponding to additive perturbation and multiplicative perturbation are proposed. Considering the factors such as H∞ performance, control input constraint, quadratic stability, model parameters uncertainties and controller gain perturbation and so on, the output feedback non-fragile control method of satellite attitude control system under multi-objective constraint is researched. Meanwhile, the standard output feedback robust H∞ controller is designed without taking controller gain perturbations into consideration. Simulation results show that without considering controller gain perturbations, the standard output feedback robust H∞ controller can make the system have better robustness, but it is very sensitive to controller gain perturbations with a strong fragility, while the output feedback robust non-fragile controllers overcome the defects of fragility with control input constraint and have strong non-fragility and better robustness.