Robust Adaptive Control For Flexible Hypersonic Vehicles

With the rapid development of air-breathing hypersonic vehicle(AHV),control system plays a more and more important role.Due to hypersonic velocity and highly coupling between propulsion and airframe,AHV possesses some distinct problems of highly coupled model,serious nonlinearity and uncertainty.In addition,another noteworthy fact is that the slender geometry and light structure cause serious flexibility effects,resulting in significant interaction between rigid and flexibility dynamics through aerodynamic forces and moments.These facts all contribute to a challenge task to complete modeling and controller design for AHV,which has attracted growing worldwide attentions.To begin with,the longitudinal model of the flexible AHV(FAHV)is presented through the Lagrange theory,which is always called the first-principle model.By replacing the complex force and moment functions with the curve-fitted approximations,the complex high-fidelity model can be transformed into the widely used control-oriented model,Lisa model.To facilitate control system design,simulation is conducted to analyze the Lisa model,which points out the problems existing in the control system design of FAHV.Then,two typical control schemes are proposed to tackle the basic tracking control problem of FAHV with flexibility dynamics.The first control scheme transforms the control model to be completely feedback linearized and the precitive sliding mode control is proposed based on the feedback linearzation technology.The other scheme tranforms the control model to be the strict-feedback form,and the dynamic surface control can be used conveniently.By comparison,the second scheme is demonstrated to be more suitable for the AHV with flexibility dynamics.Furthermore,the robust control problem of FAHV with multiple uncertainties is investigated.The resources of the uncertainties and influences are analyzed,which can be regarded as the basis of the proceeding control scheme.The first sheme proposes the adaptive laws to approximate the upper bound of the lumped uncertainties and then the robust compensating controller is designed to attenuating the influence of the lumped uncertainties.Though this scheme shows good performance,it is conservative.To reduce the design conservation,the nonlinear disturbance observer(NDO)is further designed to estimate the lumped uncertainties online and compensating it with high precision and good robustness.In addition,an effective control scheme is proposed to address the robust control problem of the FAHV subject to actuator dynamics.Different hyperbolic tangent functions are carefully designed to approximate the non-smooth saturation functions.The compensators are further introduced for saturation approximations with the Nussbaum function technique.Through Lyapunov stability analysis,the closed-loop system is guaranteed to be semi-globally uniformly ultimately bounded(SGUUB).Moreover,the tracking errors and estimation errors converge to an arbitrary small neighborhood around zero.Finally,a novel control scheme is proposed to address the robust tracking control problem of the FAHV subject to unknown dynamics and unmeasurable states.The whole control architecture is constructed using fuzzy logic system(FLS)based on the decomposition of the vehicle dynamics into the velocity and altitude subsystem.In order to improve control precision,a nonlinear observer is designed to estimate and further compensate the approximation error of FLS.In addition,a fuzzy state observer is proposed to estimate the unmeasurable states and reconstruct the full states of the system.Extensive simulation and evaluations illustrate effectiveness of the proposed scheme.