Attitude Dynamic Modeling And Robust Control Of Space Solar Power Station

As a potentially renewable energy system,the space solar power station(SSPS)has received much attention in recent years.However,due to the ultra-large structural dimension,extremely low structural fundamental frequency,high area-to-mass ratio,and very long operating time,the research on dynamics and control for the SSPS is a difficult and challenging problem.In order to ensure excellent solar energy collection and high efficiency of energy transmission to the earth,most of the existing SSPS configurations require three-axis stable attitude control to maintain continuous sun and earth tracking.Therefore,this paper mainly focuses on the attitude dynamics and sun/earth tracking control of the SSPS.According to the configuration characteristics,the SSPS can be divided into two types:the centralized SSPS and the decentralized SSPS.The centralized SSPS usually consists of a super large structural platform and several appendages.Since the mass and inertia of the appendages are far smaller than those of the structural platform,the attitude control of this configuration is a single-body attitude control problem.The decentralized SSPS is composed of many large flexible structures which are connected by the hinges,and the multi-body characteristic is obvious.The attitude control of this configuration is a multi-body attitude control problem.In this paper,two typical SSPS configurations,Abacus-SSPS and MR-SSPS,are taken as the research objects to study the attitude dynamic modeling and control design of single-body and multi-body of the SSPS.The aim is to develop the attitude dynamic model and robust control method of such large space structures in orbit,and provide valuable reference for the construction of the SSPS in the future.The main work of this paper is summarized as follows:(1)The single-body attitude dynamic modeling issue of the Abacus-SSPS is studied.Firstly,based on the floating frame formulation,the dynamic model of a general large flexible space structure is established through Lagrange equation of the second kind.Then,the Abacus-SSPS is simplified as a large flexible plate,and the nonlinear attitude dynamic models in both locally attached frame and linear mean axis frame,and associated linearized attitude dynamic models in the inertial orientation are derived.Finally,the influence of the gravity on the structural vibration is studied.The results show that the elastic vibration of the structure is not excited by the gravity,and the dynamic models in the two different floating frames are equivalent in describing the problem.(2)A robust enhanced control method using multiple sensors is proposed to achieve the inertially oriented attitude control of the Abacus-SSPS.The method depends on the proposed linearized dynamic model using linear mean axis frame,and the control-structure interaction is considered as the control/observation spillover rather than the inertia coupling problem.The rigid-body dynamic model is used for the design of the controller,which consists of the feedforward,time-invariant output feedback,internal model feedback,and time-varying output feedback compensation.Through replacing the output of a sensor with the weighted output of multiple sensors,the observation spillover is significantly reduced and the control-structure interaction is solved.The optimization criteria for multiple sensors in both time and frequency domain have been also proposed.Numerical simulations are also provided to demonstrate that the proposed control strategy can guarantee the inertial orientation accuracy of the Abacus-SSPS.(3)The multi-body attitude dynamic modeling issue of the MR-SSPS is studied.Comprehensively weighing the attitude control requirements,the amount of solar energy harvesting loss,the magnitudes of external disturbance torques and the control-structure interaction,the attitude orientation of the MR-SSPS is given,and the flexible multi-body attitude dynamic model is derived based on Lagrange equation of the second kind.The established dynamic model and numerical simulation results reflect that the antenna is in the"free-floating" state,and the coupling between the central truss structure and the antenna is negligible.Two simplified dynamic models are also derived and used for the control design of the MR-SSPS.(4)For the problem of sun and earth tracking during the normal operation of the MR-SSPS,a hybrid high-low bandwidth robust controller is proposed.The low-bandwidth robust controller,which combines feedback linearization and disturbance observer,is used to achieve the coarse attitude control of the central truss structure and subarrays and meanwhile avoids the control-structure interaction.The high-bandwidth robust controller,which uses collocated torque actuators and sensors,is used to achieve the precise pointing control of the antenna and meanwhile minimizes the influence of the attitude control system on the structural vibration.Numerical simulation results based on the flexible multi-body attitude dynamic model are provided to demonstrate that the proposed control method can guarantee sun and earth tracking accuracy of the MR-SSPS.(5)For the problem of the rapid reorientation control of the antenna,a control method combining the phase plane controller and the high-bandwidth robust controller is proposed.The phase plane controller,whose parameters are determined by the two objective optimization problem of minimizing the adjustment time and fuel consumption,is used to achieve the rapid attitude adjustment of the antenna.The high-bandwidth robust controller is used for achieving the final attitude stability of the antenna.Numerical simulation results demonstrate that the proposed control method can achieve the rapid reorientation of the antenna and avoid excessive fuel consumption.