Study On Control Problem For The Flight Mode Transition Of Tiltrotors Based On Switching Method

Tiltrotor aircraft is a new type of aircraft,which contains the advantages of the helicopter and fixed wing aircraft.Take-off and landing are not restricted by terrain environment,and the tiltrotor has the characteristics of high speed cruise and long distance transportation.With the nacelle tilting,the tiltrotor has three modes: helicopter mode,transition mode and fixed wing mode.In transition mode,the tilting of the nacelle leads to the changes of the tiltrotor speed and the aerodynamic layout.Therefor,the design of the transition flight control system is a difficult and key point for the study of tiltrotor.The dynamic modeling of tiltrotor is the basis and key to study the tiltrotor control problem.In order to get accurate dynamic model,we use the split method to establish the model of department pattern of the tiltrotor,i.e.,rotor,wing,body,horizontal tail,vertical fin five parts model.Because the structure of the tiltrotor is symmetrical about the longitudinal plane,the dynamic model can be decoupled by establishing transverse and longitudinal dynamics models separately.In this thesis,we study the longitudinal dynamics model of tiltrotor.Because the transition dynamic model parameters of the tiltrotor will change with the variation of nacelle angle,different flight modes have different dynamic characteristics.Thus a single system model can not meet the requirements for control precision.In this thesis,the tiltrotor longitudinal motion is modeled as multimodal switched system.In practice,the transition of the tiltrotor needs to be completed in a limited time.In this paper,based on the average dwell time method,the sufficient condition for finite-time stabilization of the tiltrotor during the transition flight is developed.Meanwhile,the design schemes of controller aching strategy are given.Finally,simulation studies are used to demonstrate that a smooth transition of tiltrotor transition modes can be implemented effectively by the proposed switching control strategy.Finally,the optimal control problem of the transition process of tiltrotor is studied in this thesis.Based on the control parameterization method,a new time variable is introduced into the time scale conversion to map the changing switching point to a fixed time point.Then,the complex optimization problem is transformed into standard parameter selection problem.Finally,the simulation results show the effectiveness of above method.