Research On Sliding Mode Based Spacecraft Actuator Fault Diagnosis And Fault-Tolerant Control

As one of necessary abilities for spacecraft autonomous operation, fault diagnosis andtolerant control is not only an key supporting technologies in the development of spaceintelligence autonomous control, but also a new way for improving the reliability,maintainability and effectiveness. However, the main idea of present methods is monitoringand analyzing elementary data at ground station to obtain the health evaluation, diagnosis andsystem reconstruction, which lack of autonomy and fault-tolerance property. The paper focuson sliding mode observer based faults diagnosis and faults tolerant control and its relatedtechnologies, in which the main works are design effective sliding mode observer and faultreconstruction algorithm to implement the faults accommodation of spacecraft andfaults-tolerant control when Fault information is unknown. The paper’s main work and resultsare as follows:Spacecraft dynamic model of fault-free is established and then describe the faults withfaults actor. According to Lipschitz nonlinear system, an type of sliding mode observer andfaults accommodation strategy are designed, the effect of high frequency chattering or therequired condition of sliding mode are analyzed. Also, spacecraft attitude controller based ontraditional sliding mode control and system global convergence is demonstrated.According to the problem of faults diagnosis and reconstruction with unknown input andactuators faults, an adaptive robust sliding mode observer is designed based on the establishedspacecraft state-space equations when yaw-axis information are not completely observable.By two coordinate transformations, the proposed approach could decouple the faults andunknown input and improve the faults estimation sensitivity and robustness. The switchingterm with adaptive feature makes the state prediction and output error bounded andconvergent. Considering the high frequency chattering problem caused by state switching oftraditional sliding mode, the paper use high-order sliding mode observer instead of thenonlinear control input by the designing linear control input signal and avoiding the highfrequency chattering due to discontinuous function. When output noise is exist, a novel robustoptimal sliding mode observer based on H∞control combined with Schur lemma and LMImethod is presented. Through this method, not only the robustness to disturbance inl2significance and H∞gain can be satisfied, but also inhibit the effect of output noise andunknown disturbance. Considering the active fault-tolerant control problem with the faults information,spacecraft active fault-tolerant strategy is proposed based on fault accommodation and statefeedback control theory. By pseudo-inverse theory, the designed nonlinear faultaccommodation controller is designed to deal with the nonlinear and model uncertainty factor,which includes two sections: nominal controller and additional controller. In the faults-freecase, the nominal controller is applied, conversely, use the additional controller.With thismethod, dynamic performance of the faults system is guaranteed. According to faultaccommodation of partial actuator faults, a novel method is proposed by solving Riccatifunction. Through this method, fault system motion trajectory could approximate the nominalsystem trajectory and guarantee the fault system uniform stability. Finally, the system stabilityis proved by using Lyapunov theorem and Barlalat’s lemma.Confront with engineering application constraints, adaptive sliding mode control basedfault-tolerant control is proposed according to partial actuator faults is occur while the faultsinformation cannot be obtained accurately. Considering steady-state error caused by boundarylayer in the sliding mode control, proportion-integral link is integrated with sliding modedesign. An adaptive control with using the adaptive update law is designed to deal withuncertainty parameters. The approach could inhibit the steady-state error of attitude controland enhance the system robustness. A novel method for designing fault tolerant controller isproposed based on adaptive fast terminal sliding mode control for control problem ofspacecraft. In this approach, a robust controller based on fast terminal sliding mode controlscheme is designed in the absence of fault detection and diagnosis through adaptive approachwhich applied to estimate the fault value of actuator. Through this approach, the closed-loopsystem globally asymptotically stability and fault tolerant control achieved within the finitetime. Meanwhile, confront with the output restriction of actual system actuator, saturationamplitude is introduced significantly. The proposed adaptive sliding mode fault-tolerantcontroller and adaptive law which independent on rotation inertial with strong robustnesscould force the output value less than saturation amplitude and solve fault-tolerant control anddisturbance rejection problem of input constraint spacecraft. All the proposed control systemstability is proved by Lyapunov theory. Numerical simulations have demonstrated that theproposed approach could implement the spacecraft attitude fault-tolerant control andguarantee system reliability.