Attitude Fault-tolerant Control Algorithms Research For Flexible Satellite During Orbit Control

Satellite technology is closely related to human life wit h the development of space science and technology,specific on-orbit satellite tasks can hardly be accomplished wit hout attitude control system.Due to complex structure,long working t ime,variety tasks and inevitably environment disturbances such as radiation and solar photovolta ic,the actuators of on-orbit satellite are easy to fail.Once actuator fault occurs,the controllability and stability of satellite attitude control system will be significantly reduced,this will leads to uncontrollability,which causes human,material and financia l resources loss,and generating significant security danger.At present,scholars have done extensive researches on fault-tolerant control of the on-orbit satellite attit ude system,and mainly concentrated on the normal operation on-orbit stage without considering the effect of coupling between attitude and orbit.However the impacts of orbit control force of flexible satellite during orbit control stage are less considered.Different from other stage,the orbit control force will provoke vibration to the flexib le attachment,therefore the satellite attitude is greatly affected by the orbit control force due to the coupling between attitude and orbit,and the impact of which is much greater than other period.Despite strong disturbance and coupling,attitude control system also has the characteristics of nonlinear,time-varying parameter and uncertaint y.Under this background,this paper presents actuator fault tolerant control approaches to solve the attitude stabilization and attitude tracking problem in presence of nonlinear factors such as parameter uncertaint y,unknown interference and input saturation of flyw heels.Research contents are proceed as follow:As the theory basis of subsequent attitude stability control and the attitude tracking control,dyna mic models and kinemat ics models of flexib le satellite attitude control system during orbit maneuver stage are establis hed,and attitude tracking model is given based on the coordinate transformation.Furthermore,the causes of attit ude control system faults are investigated,and several common types of actuator failures are summarized into multip licative fault and addit ive fault.Finally,the mathematical actuator failure models are given and summarized.Considering the problem of flexib le satellite attitude control in presence of actuator partial fault,environmental interferences and wit hout actuator redundancy backup,a backstepping adaptive attitude stabilization and attitude tracking fault tolerant control strategy is put forward based on nonlinear disturbance observer.Firstly,based on precise robust differentiator theory,a nonlinear disturbance observer is designed to suppress the effects of interference.O n this basis,backstepping based adaptive attitude stabilization and attit ude tracking fault-tolerant control method is put forward with robust compensation term to compensate actuator faults,the difficulty in obtaining minimum fault fa ilure parameter is therefore solved by adaptive control method,and the attitude stability and tracking perfomanceis achieved.In addit ion,to improve the accuracy of attitude control,an optimal quadratic based active vibration suppression controller is designed for the flexible vibration structure,piezoelectric element is used on the basis of attitude stability,and thus the elastic vibration of flexib le structure is effectively suppressed under the requirement of system performances and control inputs.Finally,the designed backstepping adaptive attitude stabilizat ion method,attitude tracking fault-tolerant control method and active vibration suppression control method are used for the flexible satellite attitude control system.The simulation results demonstrate that the control approaches can not only meet the fault tolerant performance in presence of actuator partial failure,but also effectively restrain the flexible structure vibration.An attitude fault-tolerant control problem of flexible satellite during orbit control is studied in presence of mult i-type actuator faults(includ ing complete fault,partia l fault,deviation fault and ramp fault),inertia parameter uncertaint ies and internal,external disturbances.Sliding mode control based adaptive attitude stabilization and attitude tracking fault-tolerant control method is proposed with redundant actuators.More specifically,this method not only inherits the advantages of sliding mode control,which can not only effectively deal wit h the influences of interference and inertia uncertaint ies,but also reduces the complexity of the controller and avoids the troublesome of control parameter selection by using the adaptive parameters.In addit ion,in order to avoid the "chattering" problem of tradit ional sliding mode control,a hyperbolic tangent funct ion based adaptive slid ing mode fault tolerant control strategy is proposed,and this method is applied to design satellite attit ude control law.Simulation results demonstrate that the improved fault tolerant control strategies can ensure the good fault tolerant ability of the closed-loop system,and avoid the "chattering" phenomenon as wel.To solve the actuator input saturation problem,a hyperbolic tangent funct ion based sliding mode adaptive attitude fault-tolerant control a lgorithm is proposed,disturbances,uncertain inert ia parameters,and mult i-type actuator faults are also considered.This control algorit hm explic it ly considers the saturation magnitude of the available actuator input amplitude by introducing the hyperbolic tangent function,thus the input torque can be limited within the amplitude.Moreover,control parameters of sliding mode are classified into constant and variable,and the linear and nonlinear sliding mode adaptive attitude fault-tolerant control algorit hm are designed respectively.In both algorithms,the adaptive control strategies are used to adjust the on-line sliding mode control parameters,which greatly improve the system performance with uncertain parameters,disturbance “ chattering ” and mult i-type actuator faults.The numerical simulation results show that the proposed fault-tolerant control algor ithm can effectively improve the system performance in presence of input constraints,realize attitude stabilization and attitude tracking ability are realized in presence of multi-type actuator faults.