Modeling And Control Research Of Stratospheric Airship

In view of the military and civil value of stratospheric airships,various major aerospace countries have drawn up stratospheric airship project plans,actively carried out feasibility studies,key technologies and flight tests.However,all of them are still in the experimental stage.This paper focuses on the cruise process of stratospheric airship,including its path planning and trajectory tracking control,and then studies the rising and falling stages of stratospheric airship,mainly the combined control of pressure difference and velocity.The main contents are as follows:(1)The kinematics model and dynamics model of stratospheric airship.Firstly,the parameters and coordinate systems used to establish the model are introduced.Secondly,the kinematics model is derived according to the relationship between the coordinate systems.Finally,the force analysis is carried out,and the complete dynamic equation of six degrees of freedom is established according to the Newton-Euler equation.A simplified dynamic model of stratospheric airship in cruising and longitudinal flight are given respectively,which will be applied to the later research.(2)Thermodynamic model of stratospheric airship in ascending and descending process.Firstly,the variation of external atmospheric environment with height is introduced.Secondly,the heat exchange between the airship and the external environment during the rising process is introduced.Finally,the thermodynamic model is established according to the equation of state of ideal gas and the first law of thermodynamics.(3)Path planning of stratospheric airships during cruise.The path planning of stratospheric airship first needs to transform the infinite dimension optimal control problem into the nonlinear programming problem,and some optimization algorithms are used to solve the optimal solution.In this chapter,Gauss pseudospectral method is chosen to discretize the optimal control problem,and SQP algorithm is used to obtain the optimal solution.Finally,the result of planning is obtained by simulation in MATLAB/SNOPT,and the simulation results of obstacle avoidance after adding path obstacle are given.(4)Trajectory tracking control of stratospheric airship cruise.Firstly,a simple feed-forward PD single loop control is designed and its stability is analyzed to verify the system’s controllability.Then a single loop sliding mode controller is proposed,using the simulation results to verify the control effect.Finally,in order to improve the shortcoming of single loop sliding mode control,long dynamic response time and,a double-loop sliding mode control is proposed,and the parameters of sliding mode controller are adjusted on-line by combining fuzzy control for the high tremor of sliding mode control.Finally,adaptive control is added to estimate the uncertain parameters online.The model of the controller is built in MATLAB/Simulink,and the simulation results of the controller are obtained and analyzed.(5)Composite control of differential pressure and velocity of stratospheric airship in ascending and descending process.According to the desired pressure difference,the height and speed of the position and the current actual pressure difference produce control signals acting on the valve of the air bag for suction and exhaust control,so as to maintain the internal and external pressure difference.The differential pressure loop controller uses PID control.Then according to the designed reference rise and fall trajectory,The error between the actual trajectory and the ideal trajectory and the actual mass and atmospheric density produced by the thermodynamics control loop act on the vectoring thrust device and the elevator to track the ideal trajectory and make the stratospheric airship rise and fall steadily.A speed tracking controller is designed by using a backstepping controller.Finally,the thermodynamic coupling model and composite controller are built in MATLAB/Simulink,and the simulation results are obtained.