| The boost phase is the first phase of the hypersonic flight test and the key phase of mission.This phase has complex flight environment,strict process constraints,and the stability of the aircraft,which is a grim challenge for control of the boost phase.In this dissertation,we research the longitudinal control technology of boost phase with the aim of engineering,which provides a solution for hypersonic vehicle to flight with rocket boost.Firstly,the trajectory design method based on the pitch angle is studied.According to the motion characteristics of the aircraft,the shape of the pitch angle profile is planned.On this basis,the pitch angle profile is designed into three phases: the vertical phase,the turning phase and the aiming phase.The nominal trajectory satisfying the constraints is designed in segments,which solves the problem of tracking the pitch angle under multi-constraints to complete the flight mission.Secondly,aiming at the adaptability of longitudinal control variables concerning stability and flight missions,The control strategies of angle of attack and pitch angle are compared from root locus,frequency domain analysis,simulation and verification.It is found that better control results can be obtained by using pitch angle control.On this basis,two kinds of stabilization control structures,namely the pitch rate damper inner loop and the pitch rate command inner loop are designed.Their performance differences are compared from time domain,frequency domain and robustness.The results show that the inner loop of the pitch rate command can adapt to different working points with great stability difference and has strong control ability,which provides a better solution for safe flight.Finally,aiming at the uncertainty of the angle gauge,and angle of attack will bring the flight control and overrun the driving force of abnormal problems,an angle of attack protection strategy based on longitudinal pitch control is proposed.The relationship between pitch angle and angle of attack is analyzed in terms of motion mechanism.The control deviation constraint of pitch angle is proposed to restrain the angle of attack indirectly and feed the angle of attack back to the pitch command.Thus,the two control laws of angle of attack protection are directly constrained.The realization of the system in flight control system is given.The validity of the control law is verified by analysis,design and a large number of uncertainties simulation. |
