Research On Compound Control Design Methods For Spacecraft Attitude

Attitude control is the fundamental requirement and important guarantee of space-craft to fnish all kinds of the space missions. The attitude dynamics is also of seriousnonlinearity during spacecraft attitude maneuver. The spacecraft system is subject toinertia uncertainties of spacecraft and all kinds of external environmental disturbances.Besides, control input saturations and actuators faults should also be taken into accountin the practical application. Recently, with the structures and tasks of spacecraft beingmore and more complex, the requirements of spacecraft attitude control algorithms areincreasingly high. A single algorithm cannot provide optimal multi-performance indicatorsof attitude control for the spacecraft system in the presence of internal uncertainties andexternal disturbances. In this thesis, the attitude control problems are solved by slidingmode control (SMC) combined with extended state observer (ESO), disturbances observer(DO), robust control and adaptive control, respectively, to design several compound controlstrategies to provide rapidity, robustness, accuracy and anti-wasting energy simultaneous-ly. Terminal SMC (TSMC), super-twisting algorithm and anti-chattering technology arefurther improved. Finite-time stability proof of TSMC combined with adaptation is frstachieved. The main content of this thesis can be summarized as follows:1. This thesis investigates the fast and high-precision attitude tracking control problemfor rigid spacecraft under actuator saturations, inertia uncertainties and external distur-bances. An optimized spacecraft dynamic equation is obtained by appropriate algebraicmanipulation, which can not only alleviate dramatically the burden of observer but alsoimprove the accuracy of ESO and DO. Due to accurate estimation of uncertainties and dis-turbances by observer (ESO or DO) and fast response provided by SMC and backsteppingtechnique, the compound control law that is composed of SMC and observer (ESO or DO)can achieve high-performance attitude tracking control. Furthermore, the disadvantages ofSMC, which sufer chattering, and ESO, of which the uncertainties and disturbances maybe beyond the observability, can be remedied by each other.2. Based on nonsingular terminal sliding mode control (NTSMC), this thesis investi- gates the fnite-time attitude stabilization problem of the spacecraft system. First, robustNTSMC (RNTSMC) is proposed to provide fnite-time attitude stabilization. Then, adap-tive NTSMC (ANTSMC) is presented, in which adaptive technique is applied to estimatingand compensating uncertainties and disturbances, and NTSMC presents rapidity and ro-bustness. It requires no information on inertia uncertainties and external disturbances, soit can be used in practical systems, where such knowledge is typically unavailable. By es-timation of uncertainties and disturbances via adaptation, the chattering can be alleviatedefectively. Finite-time convergence proof of ANTSMC for the spacecraft system is frstpresented, and the explicit expression of small regions bounds is provided.3. Based on fast nonsingular terminal sliding mode (FNTSM) control (FNTSMC),the fnite-time attitude tracking control problem for spacecraft system is addressed. First,FNTSM surface (FNTSMS) without any constraint is designed, which contains the advan-tages of the nonsingular terminal sliding mode and the conventional sliding-mode together.Then, fve SMC laws by employing FNTSMC associated with adaptation provide fnite-time global convergence and avoid singularity problem and chattering phenomenon. Theydo not need any knowledge of inertia uncertainties and external disturbances. In lightof novel control architecture, the chattering caused by SMC has been resolved absolutely.Based on the Lyapunov stability theory and fnite-time technique, the fnite-time attitudetracking of adaptive FNTSMC (AFNTSMC) for spacecraft system, the explicit expressionof small regions bounds and theoretical basis of tuning parameters are presented.4. Based on “equivalent control”, this thesis is also concerned with the fnite-timeattitude tracking control problem for spacecraft system under low energy consumption.Adaptive-gain super-twist algorithm (STA) and adaptive-gain FNTSM control algorithm(FNTSMCA) are proposed, respectively. The proposed controllers can provide rapidity,robustness, accuracy and anti-wasting energy simultaneously. Two interconnected obsta-cles for application of SMC–chattering and high activity of control action are resolved.Compared with standard STA, the modifed STA includes some merits: i) it dose notrequire any knowledge of inertial uncertainties and external disturbances; ii) it can pro-vide strong robustness against spacecraft inertia uncertainties and external disturbances growing in time or together with the spacecraft state variables; iii) the adaptive gains canovercome non-overestimating drawback and resolve robust gains being selected difcult-ly; iv) it provides faster convergence speed than standard STA. Two fnite-time rigorousconvergence proofs for spacecraft attitude tracking system driven by adaptive-gain STAand adaptive-gain FNTSMCA, respectively, are given. An estimation of the convergencetime and accurate expression of convergence region are also provided. The novel AGSTAincludes the merits of standard STA, fast reaching laws and adaptation.5. This thesis also considers fnite-time fault-tolerant attitude control for spacecraftsystem even though inertia uncertainties, external disturbances, actuator saturations, andeven actuator faults afect the system. Part I: Consider fnite-time fault-tolerant attitudestabilization control problem. Based on FNTSMS, robust FNTSM control law (RFNTSM-CL) and adaptive FNTSM control law (AFNTSMCL) are proposed to ensure that thespacecraft system trajectory fast converges onto the FNTSMS and fast evolves to smal-l region in fnite time. For the practical implementations, the proposed ANFTSMCLis modifed in real sliding mode context. The proposed control laws provide fnite-timefault-tolerant attitude stabilization and high performance of spacecraft attitude control.Rigorous proof of fnite-time attitude stabilization for spacecraft system is presented. PartII: The proposed compound control composed of FNTSMC and adaption resolves fnite-time attitude tracking control of the spacecraft system. The proposed controller can achievefault-tolerant control under actuator saturations without the fault detection to obtain fault-s’ information and be robustness against external disturbances and inertia uncertaintieswithout prior knowledge of them. There are two methods to express actuator saturations.A new method to deal with total uncertainties of afne nonlinear systems is presented.A fnite time stability for spacecraft attitude tracking system is frst given under inerti-a uncertainties, external disturbances, even actuator faults and saturations. The upperbounds of the converging trajectories regions and the relationship among settling time,convergence region and the actuators faults and saturations are analytically calculated.6. Simulation results are presented to illustrate the efectiveness of the control strate-gies. Comparison simulation results demonstrate superiority of the novel control algorithms over existing methods. Besides, digital simulation results utilizing the physical parametersof spacecraft verify the efectiveness of the proposed controllers.In the end, main results in this thesis are summarized, and the prospects for the futureresearch are presented.