Research On Attitude-trajectory Decoupling Control Of Active Morphing Near-Space Solar-Powered Aircraft

Near-space solar-powered aircrafts have the ability to stay above altitude of 20 km for a long duration.Compared with conventional aircrafts,they have longer flight durations and wider cover ranges,which lead to a broad application prospects.Limited by the low density of atmosphere and the rigorous constrains on the balance of energy,high-aspect-ratio and light-weight configuration is always applied to near-space solarpowered aircrafts,leading a big challenge to their stability and safety in low-altitude flight.With morphing applied to flying-wing layout solar aircraft,multi-segment morphing aircraft are proposed by this thesis to achieve a better adaptation to the flight conditions in both high and low altitudes.Dynamic and control problems are researched on this novelty aircraft.The main contents are as follows.(1)Quick modeling of aerodynamics,dynamics and construction.As the period of aerodynamic calculation is usually very long with commercial program such as CFD,a quick aerodynamic algorithm based on lifting line theory is proposed to fit the requirements of quick calculation in concept design and primary validation.Explicit centroid dynamics equations of morphing aircraft and the required construction model of multi-segment aircraft are first built.The disciplinarian of additional terms caused by morphing are analyzed.(2)Safety climbing approach with active morphing.With the quick aerodynamic algorithm and analyses on maneuverability and stability,morphing angles are optimized for each altitude.The weight function of flight power,turbulence resistance,static stability and controllability are changing to fit the flight condition of each altitude.An optimal climbing approach from sea level to near space are obtained.The velocity and power are slightly added in low altitude,while the stability and performance of turbulence resistance are improved obviously.(3)Attitude stabilizing control research based on linear parameter varying system.Linear parameter varying modelling approach of the dynamic equations of multisegment morphing aircraft are studied.H infinity controller design approach of linear parameter varying system are researched.A criteria of stability and H infinity performance for linear parameter varying system is proposed.A H infinity controller based on state estimation of reference dynamics is proposed for linear parameter varying system.The application of this controller on the attitude stabilizing control problem shows its good performance to deal with the challenge caused by the nonlinear and non-stationary morphing processes.(4)Trajectory decoupling control based on active morphing.There exist no analytical solution of morphing command in control model,which needs be solved in real time onboard.Therefore a morphing command quick solving approach is proposed with simplification and iteration.Nonlinear dynamic revise method is applied and trajectory decoupling controller is designed based on active morphing,which decreases the influence of trajectory movements to the attitude of the aircraft.Nonlinear centroid dynamics model for morphing is used in simulations,to validate the attitude-trajectory decoupling control system with active morphing.(5)Utilization of asymmetrical morphing in lateral movement.A special asymmetrical morphing method named by lift-keeping morphing is proposed and discussed.The steady state model of non-sideslip trajectory turning and crosswind resistance flight are built.Flight states in active morphing approach and conventional attitude-change approach are compared in lateral movement.The research shows that in trajectory turning,as the curvature ascends,the flight power in non-sideslip lift-keeping morphing approach keeps constant,whereas the flight powers in rolling approach and yawing approach increase.In crosswind resistance flight,as the velocity of the crosswind ascends,the flight power in zero-side-force lift-keeping morphing approach keeps constant,whereas the flight power in rolling approach increase quickly.The flight power in yawing approach keeps constant if the loss of trajectory velocity is acceptable,otherwise the flight power have to increase to meet the constraint of trajectory velocity.The technical proposal of design matching in high altitude and low altitude of near-space solar aircraft with morphing are discussed,and the dynamics characteristics,attitude control and trajectory control in the morphing process are deeply researched in this paper.The proposed attitude stabilizing control for nonlinear system,and the attitude-trajectory decoupling control system with active morphing,provide a technical support for control system design of morphing aircrafts,an analyses approach and an application reference for exploring the design limitations of near-space solar aircraft.