Research On Modeling And Control For Near Space Airship

Near space is an airspace between the flying altitude of the aircraft and the orbital altitude of the spacecraft,it is an emerging airspace field which spans and links aviation and space.Near space airship is the most valuable military and civilian equipment of the near space craft.In this paper,the dynamic model and thermodynamics model of near space airship are studied firstly,and the hydrodynamic characteristics are analyzed too.Then,the corresponding system theoretical identification is made.Finally,some control strategies are proposed and applied to the near space airship,to control its hover stabilization,trajectory tracking,and overcome the external environment disturbance,through digital simulation and semi-physical simulation to verify the effectiveness of the control method.The research of these problems can provide technical support for the design and development of near space airship,and also can provide reference for the modeling and control of large spacecraft and other large systems.Firstly,the dynamic and thermodynamics model and hydrodynamic characteristics of the near space airship are studied.In terms of the mathematical modeling,considering the boundary layer of the airship surface due to the air viscosity.From the aerodynamic point of view,the airship soft structure will affect its aerodynamic force and torque,which has a special flight characteristics.In order to facilitate the establishment of the airship dynamic model,a theoretical system is constructed to integrate flight dynamics,structural dynamics,aerostatics and aerodynamics,and the theoretical model can be used to implement the airship dynamic simulation and aerodynamic elastic stability analysis.Based on the theory of potential flow and aerodynamics,this paper studies the coupling between aerodynamics and elastic deformation of airship,and deduces the model of airship dynamic model.The model includes flight dynamics,structural dynamics,statics and aerodynamics.It provides the theoretical basis for studying the dynamic characteristics of flexible airship.Secondly,for the near-space dynamic model in different environments,using the input and output observation data pair,using the auxiliary variable variance method and maximum likelihood method respectively to establish their corresponding identification estimation model.For non-parametric identification of frequency response function estimation,combining the frequency response function,the initial-final conditions and impulse response parameters as a identified parameter vector,so as to convert the former problem of frequency response function estimation to a linear least square optimum problem.According to the special structure of this optimization problem,it is proposed to use the separable steps to realize the frequency response function estimation.Aiming at the identification and estimation of the frequency response function in the airship elastic deformation vibration,the nonparametric identification method of frequency response function estimation is studied.In the discrete Fourier transform,the influence of the transient leakage term and the observed noise spectral term on the estimation of the frequency response function is considered.Then,a new method is proposed,which is suitable for the hovering stability control problem of the airship.The reverse flight control strategy is designed to stabilize the hovering flight of the airship,which is robust to disturbances(wind and turbulence).The control system with time delay is transformed into a control system with no time delay by using the idea of continuous state transformation.The system with no time delay is used to minimize the performance of the system,Then the relationship between time-delay feedback control and state-controlled optimal control is obtained,and the gain of optimal time-delay feedback control is obtained.Finally,the simulation is carried out.The nonlinear combination of the saturation functions of the linear feedback ensures that the problem of global stabilization of the actuator under saturation is fundamental to the under-excitation system and thus constructs a control strategy to deal with the problem of lateral failure of the airship,From a current state to a desired reference path of the desired state,thereby reducing the need for lateral forces.Finally,a non-fragile control method based on the coprime factor perturbation system is proposed to track the spacecraft's tracking demand.The sensitivity,robust stability and non-fragility of the system are discussed.The system should have a good ability to suppress interference,while the sensitivity is reflected in the system sensitivity to interference.The problem of the robust stability and non-fragile control of closed-loop system is studied for the system with structured uncertainties both in plant and controller.Non-fragile robust stability and performance sensitivity of the closed-loop system with left coprime factor perturbations and right coprime factor perturbations are investigated respectively,and the sufficient conditions are given for the non-fragile robust stability of perturbed system under the certain conditions as well.At last the relation of non-fragile robust stability between the two aspects is given.The nonlinear dynamics and kinematics modeling of the airship are re-exported and rearranged in the form of state space representation.The performance of the trajectory tracking controller is simulated by mathematical simulation.It tracks the given reference trajectory and state variables,and shows the trajectory tracking Error is small enough,with good tracking performance.