Studies On Attitude Determination And Control System Key Technologies Of Three-Axis Stabilized Satellite

The attitude control system is the key part of satellite, which determines the realization of in-orbit functions in some degree. To guarantee long-time running with high accuracy, high credibility and high stability of satellite, the pointing precision and stability must satisfy requirements. The thesis researches on several key technologies, including star sensor measuring algorithm, attitude determination algorithm based on robust H∞filter and attitude tracking control algorithm based on sliding mode control. The simulation results and analysis prove that the proposed methods can guarantee imaging precision of payloads on satellite. The main works and results are as follows:First, relative math models of satellite attitude control system have been built, including attitude dynamics, attitude kinematics, orbit dynamics, measuring vector reference models, actuators math models. And conventional coordinates, attitude description methods have been defined; in-orbit working modes and the transformation relationship also are introduced.Then, technical indexes, working modes and error sources of star sensor have been presented simply, and simulation of observed catalog has been realized. Furthermore, attitude measuring methods have been paid attention to. Navigation star database by SAO catalog is built, then the methods of pretreatment and centroids positioning of observed catalog are given. Several existing star pattern recognition methods are summarized. The thesis has proposed a new improved grid algorithm based on log-polar transformation. By LPT two dimension feature vector has been reduced to one dimension, a new feature vector rule has been designed here, navigation star database has been built and searched by data structure Hash table. Simulation results show that this new method can improve performance indexes of star pattern recognition algorithm.Third, the principle of vector determination methods is given. Then discrete EKF has been applied to the combination of star sensor and gyro, deriving error models, estimating attitude and other parameters, analyzing the influences of filter intial values. System model of star sensor and gyro which is nonlinear time variable system has been transformed into linear time invariant system. Robust H∞filter is used to estimate attitude parameters, building robust filter equation, deriving augmented filter error equations. According to bounded real lemma and Schur supplement lemma, restricted condition by transfer function of H∞norm is transformed into matrix inequality, by using of variable substitution method the linear matrix inequality of robust filter coefficient matrix can be got. Then, status errors can be resolved iteratively.Introducing delta operator into robust H∞filter, deriving filter error equation, by bounded real lemma and Riccati inequality matrix inequality with sampling period has been derived. Another new matrix inequality is deduced by Schur supplement lemma. ILMI method is used to resolve these two inequalities, and minimum disturbing attenuation factor y can be solved out. Then robust filter coefficient matrix can be derived by filter error equation coefficient matrix when parameter y reaches stable. And attitude parameters can be estimated iteratively. This algorithm has good effect in short-period system.Forth, by building error kinematic eqution and error dynamic equation, normal sliding mode controller has been used in attitude tracking control, and control law is designed, which has been compared to PD controller. A new hybrid parameter integar controller has been proposed and applied into attitude tracking control. Designing a hybrid parameter integar sliding surface, using exponential approach law as switching function, deriving control law by Lyapunove function method, and asymptotic stability of the system has been proven. Simulations demonstrate that this controller is good at convergence rate, corresponding velocity, smaller steady-state error and higher control precision.To overcome the weakness that the reaching process is of bad robustness, a gobal variable structure controller has been designed. System initial point is at sliding mode surface by constructing nonlinear switching function; combining with improved exponential approach law, chattering is weakened. Control law in the situation of bounded interference control torques has been derived, which can satisfy global robustness. Simulation results show that this global robust variable structure controller has good performance indexes, which can satisfy pointing precision and control stability requirements of three stabilized-axis satellite.