Research On The Nonlinear Constrained Control Method For Hypersonic Re-entry Flight

The hypersonic vehicle(HSV)concerns national defense security and the utilization of near space resources,and hence it has become the research focus of those military powers.The handling of re-entry flight control problems of HSV is essential for the completion of the flight mission.Among them,the complex flight environment,the saturation of control surfaces,the state constraints of attitude angles,unknown external disturbances and parameter uncertainties make the design of the flight control scheme become more complicated.Around these problems,this paper conducts the following research work:Firstly,the HSV mathematic model during re-entry flight is established.The geo-centric inertial coordinate system is chosen as a reference frame and the influence of the earth's rotation is taken into consideration in order to improve the model fitting effect of the HSV.After that,the reaction control system is coupled with the mathematical model and a more improved six degrees of freedom equations of twelve states for HSV reentry flight is deduced.Secondly,the control surfaces are likely to fall in saturation due to the rarefied air of near space area during re-entry phase.Aiming at the saturation problem,a kind of external Anti-windupcompensation system is proposed to eliminate the negative influence on the HSV re-entry attitude control.And the L2 gain is adopted as the index of performance optimization.Then,the iterative optimization algorithm based on PSO is designed to solve the matrix of Anti-windup compensation system.Combined with the nominal nonlinear generalized predictive control(NGPC)system,the saturation situation can be relieved within a short timeand the satisfactory control performancecloseto the nominal system is attained.And the attitude angles can track the given command signals smoothly and rapidly.Thirdly,considering the problem of external moment disturbance and model parameter uncertainty during HSV re-entry,a novel sigmoid function tracking differentiator based disturbance observer(STDDO)is proposed to estimate these composite disturbances.Meanwhile,an improved cooperative optimization algorithm(ICOA)is proposed since PSO algorithm is easily trapped into the local optimum value.And then a robust compound control scheme composed of the ICOA-based Anti-windup compensatorand the STDDO compensator is designed in this paper,considering the control surfaces saturation,uncertainties and interference.The simulation results show that the proposed control strategy is effective for the HSV real-time control and has a high precision and strong robustness for the composite disturbances.Finally,the controller of track angle loop for HSV re-entry flight is designed to meet the condition of quasi-equilibrium glide.Furthermore,it is necessary to impose some restraints on the flight states during HSV maneuveringin view of flight safety and maneuver quality.The control laws based on barrier lyapunov function is put forward to handle the constrained problem.In the simulation experiment,the restriction of attack angle and bank angle is configured,and the results verify the effectiveness of the constrained controller.It realizes the tracking of command signals.