Longitudinal Attitude Control Of Hypersonic Vehicle With Angle-of-attack Constraints

Attitude control system is important for hypersonic aircraft, so it is necessary to dofurther study on it. Airframe/engine integration technology is an important technologywhich can reduce the resistance of hypersonic aircraft and increase the lift-drag ratio.However, the introduction of this technology will make the air intaking performance ofscramjet be sensitive to the angle of attack. Therefore, the angle of attack is needed tomeet constraints so as to ensure proper operation of the engine. Considering thisproblem, this article mainly focuses on the longitudinal attitude control problems ofhypersonic vehicle when the angle of attack is limited. The main contents are asfollows:First, we choose the Universal cone (winged-cone) announced by United StateNASA Langley Research Center as the hypersonic vehicle model. According to theflight dynamics theory, we can deduce out the six degrees of freedom nonlineardynamical equations of hypersonic aircraft. With some reasonable assumptions, we getthe longitudinal dynamics equation. Considering the perturbation of aerodynamicparameters on the basis of the nominal model, we build longitudinal perturbation model.Then, this paper introduces the method called Barrier Lyapunov Backstepping,which can solve constraint problem. Firstly, we define the general Barrier Lyapunovfunction and describe the mechanism how Barrier Lyapunov function solve theconstraint problem. Depending on the state of the constraint interval constraints, weselect two different types of Barrier Lyapunov function for nonlinear systems with stateconstraints. Finally, the numerical simulation result of a two-order nonlinear systemwith state constraint shows that the state is limited.After that, we design the attitude controller by Barrier Lyapunov Backsteppingtheory for the nominal longitudinal model of hypersonic vehicle, explicitly consideringthe constraint problem of the angle of attack. Comparing with the controller designed bythe classic backstepping, the controller designed by Barrier Lyapunov backstepping canensure that the angle of attack satisfies the constraints.Finally, we study the parameter perturbations problem in attitude controlling. Thefunction with parameter uncertainty is expressed in the form of linear parameters. Weintroduce the quadratic estimation error function in the design of Lyapunov function toget the virtual control command and the adaptive law. Then the uncertainty issuppressed. Finally, the numerical simulation shows that the system has good stabilityand robust performance.