Adaptive Attitude Control For A Heavy-lift Launch Vehicle

Heavy-lift launch vehicle(HLV),as a powerful delivery vehicle,represents the highest level of launch vehicle technology in the world.It can not only significantly enhance the capability of entering space,but also act as an important basis for space exploration and large-scale space activities.In order to satisfy the mission of China's space station,Chang'e lunar exploration,Mars exploration,deep space exploration,manned moon landing or Mars landing and other tasks,the research on HLV is essential and it can dramatically improve China's space science level and space exploration level.This paper aims at the adaptive attitude control system design for HLV,three key problems are considered including how to further improve the performance of PID controller,how to restrain strong couplings,large external disturbances and uncertainties and how to ensure attitude stability in the case of engine servo mechanism failure.The main research contents are as follows.Firstly,parameters of the HLV are carried out based on relevant empirical formulas and known information,which mainly including aerodynamic parameters,elastic vibration modal parameters,liquid sloshing parameters and mass characteristic parameters.The couplings of rigid motion,elastic vibration and liquid propellant sloshing for HLV are strong in the presence of large slenderness ratio,lower stiffness,lower first order vibration frequency in contrast to general launch vehicle,and the coupling of local elastic modal of booster and elastic vibration modal of core stage.In order to avoid the complication of the model and facilitate the design of the control system,the elastic vibration and sloshing coupling dynamics model of HLV is established by Euler method,which lays a foundation for the subsequent control system design of HLV.Small disturbance linearization equations are carried out based on the elastic vibration and sloshing coupling dynamics model of HLV.Therefore,the corresponding transfer function is obtained,and the PD controller with fixed coefficient correction network is also designed.However,traditional PID control is difficult to deal with strong disturbances in the process of flight such as aerodynamic uncertainty and elastic vibration frequency uncertainty that is inconsistent with the ground test such that the correction network is difficult to filter the control signal.In order to solve this problem,an adaptive augmented controller(AAC)is designed.Adaptive gain control law,disturbance compensation algorithm,optimal control allocation law and adaptive notch filter are added based on the traditional PID control,which can satisfy the requirement of attitude stability for HLV under the condition of large disturbances and vibration frequency uncertainties.Secondly,traditional PID controller cannot satisfy the requirement of attitude control accuracy because of strong couplings of vibration and sloshing,large uncertainties during flight and large external disturbances at the same time.A novel active disturbance rejection control(ADRC)based on Euler angle is presented,and a digital filter is also designed to guarantee attitude stability under the condition of the liquid sloshing and elastic vibration.By utilizing a novel nonlinear extended state observer,the external disturbances and un-modeled dynamics can be effectively estimated.Moreover,a nonlinear control law is put forward to achieve outstanding performances such as fast response and non-overshoot.In order to solve the problem of attitude singularity,a quaternion-based composite attitude control via ADRC and sliding mode control is designed which can further improve the capacity of resisting disturbance and the performance of controller.A fixed-time adaptive model reference sliding mode attitude tracking controller is designed to avoid the problems of large basic frequency because of high damping in ADRC.By utilizing a second-order reference model with expected response time and overshoot performance,a fixed-time adaptive reaching law and a fixed-time disturbance observer is presented.The proposed controller can not only realize good tracking performance,but also overcome strong internal or external disturbances and effectively suppress the liquid sloshing and the elastic vibration.In addition,a fixed-time extended state observer based sliding mode controller is designed to ensure the good convergence of the attitude tracking error and its derivative.Finally,in order to improve the reliability and anti-failure ability of the control system,an adaptive fault-tolerant control is carried out in the presence of large probability of engine servo mechanism failure especially after the booster engine is controlled.Actuator fault dynamics model is established and the typical fault mode is described.Subsequently,an adaptive augmented fault-tolerant controller is presented based on a fast fault identification observer and the proposed AAC.In order to avoid the accurate fault identification information in controller design,an adaptive fault-tolerant controller is designed by combining with a disturbance observer.