Research On Gust Load Alleviation Methods For Multi-control-effectors Aircraft

During the aircraft takeoff,cruise,approach and landing,it will inevitably be affected by the atmospheric disturbance.This influence may lead to aircraft passenger jolted,aircraft structural flutter or aircraft out of control.Gust load alleviation(GLA),as a major category of active control technology,has attracted more and more attentions from experts in the flight control research field.Usually,modern high-performance aircrafts all have the multi-control-effectors layout.The traditional way can not be achieved on them.So,it needs to consider how to solve the control problem of overdrive system.With full consideration of these factors and the influence of the environment,how to ensure that the aircraft can also fly smoothly,safely and accurately is of great significance for enhancing the flight safety of modern aircraft and improving the comfort of passengers.In this paper,the modern multi-control-effectors aircraft is taken as the research object,and several GLA schemes with higher tracking accuracy and more robustness are proposed for the situation that gusts usually occur during cruising and maneuvering flight,which will affect the aircraft safety and passenger comfort.This paper studies from modeling to control,and provides theoretical basis for GLA and its application of multi-control-effectors aircraft.The research work and main contributions of the paper are as follows:(1)Aiming at the problem of aircraft modeling under gust disturbance,the dynamic and kinematic equations are derived,the definition of gust module and its input and output are defined,and two kinds of aircraft models under gust disturbance are established.The derivation of the equations and the definition of gust module input and output can help us to understand the mechanism of the wind disturbance effect on aircraft.The establishment of the two aircraft models under gust disturbances makes the controlled objects of gust load alleviation system more standardized.The following controller designed in this paper are all based on the two kinds of controlled object models.(2)Aiming at solving the problem of overdrive system and GLA.A kind of control augmentation and control allocation based GLA method is proposed to solve the control problem of the multi-control-effectors aircraft overdrive system and the compatibility of gust load alleviation systems with the main flight control system.The generalized inverse and surface search control allocation methods are used in the control allocation method.On the one hand,this method can dynamically distribute the ideal angular velocity to ensure that the aircraft can maintain its original attitude.On the other hand,the negative value of additional normal overload or additional lateral overload can be allocated,which can effectively reduce the additional normal overload or additional lateral overload caused by gust.(3)This paper presents a longitudinal GLA method based on L1 adaptive,nonlinear dynamic inversion and control allocation.The method divides the aircraft state into three loops: fast loop,medium loop and slow loop based on the principle of time scale separation and singular value perturbation.The gust disturbance aircraft model considering the interference angle of attack is adopted.It is considered that the wind disturbance affects the aircraft from inside to outside.Therefore,if L1 adaptive control method is used to stabilize the innermost fast loop,the middle and outer layers will not be affected by wind disturbance.This method can make the controller rapidity compatible with robustness.(4)This paper presents a GLA method based on modified active disturbance rejection control(MADRC)and real-time direct lift compensation(RTDLC)control allocation technology.This method can improve the speed and control precision of ADRC simutaneously.In order to reduce the additional overload of the aircraft as much as possible without changing the flight status and attitude,this paper extends the three-axis moment/moment coefficients of traditional control allocation to lift/lift coefficients.This method is called real-time direct lift compensation(RTDLC)control allocation method in this paper.This method can give full play to the characteristics of multi-control-effectors aircraft,so that the aircraft can not only fly normally,but also complete the task of reducing the additional overload.(5)In order to solve the problem of alleviating the omnidirectional gust,and to have the function of state constraint and limited tracking error accuracy,this paper presents an omnidirectional robust gust alleviation method by disturbance observer based barrier Lyapunov function backstepping(DOB-BLBS)and disturbance observer based nonlinear dynamic inversion(DOB-NDI).This method can effectively confine the intermediate state of the backstepping method to the safe boundary by designing the candidate barrier Lyapunov function.It can also remedy for the relative sensitivity of the traditional backstepping method,and remedy for the inadequacy of the traditional dynamic inversion method which is extremely sensitive to modeling errors and external disturbances.