Research On Electric Tail Rotor And Yaw Motion Control Of Helicopter

More-electric or all-electric helicopter technology is an important development field in the aviation industry.The electric tail rotor(ETR)reduces the transmission components,noise and vibration level,and improves the system efficiency,reliability and maintainability,comparing with the traditional mechanical one,which is consistent with the green and low-carbon development concept of aviation.ETR,as the actuator of yaw motion,requires adjustable speed and pitch angle of tail rotor to achieve stable and precise yaw trajectory.However,it brings new yaw flight control modes,and its nonlinear,timevarying load and uncertain electric parameters,make it become a difficult problem that controllers guarantee the stability of ETR's speed and yaw motion in a complex flight condition.Therefore,this dissertation studies the robust and anti-disturbance techniques of ETR speed regulation system,and the problems on model perturbation,multi-source disturbance,state constraint and actuator output fluctuation under three manipulation modes.(1)A nonlinear and full-scale flight mechanics model of the unmanned helicopter is firstly constructed,including the ETR's force and torque,and mathematical model of permanent magnet synchronous motor.The aerodynamic characteristics of tail rotor on typical flight conditions,the frequency response of yaw channel and the coupling effect with the main rotor are analyzed,and then the quality requirements of yaw flight are discussed.These works provide data support and numerical flight simulation platform for the selection to driven motor,and controllers design of ETR's speed and yaw motion.(2)In view of the problems of time-varying load and uncertain electromagnetic parameters in ETR's speed system,this dissertation proposes a speed regulation method based on the unified predictive current control(PCC),giving an ETR drive controller with cascade structure of speed and current.The outside-loop speed controller is designed based on disturbance observation and compensation technique,which includes the terms of disturbance feedforward,torque prediction and nonlinear error feedback.For the inside-loop current controller,the proposed unified calculation method integrates three types of PCCs into one control framework,a variable-period identification algorithm is designed to obtain accurate current model even in noise environment,thus after finishing identification,current controller is able to switch to a higher-precision PCC method.Comparative simulation results verify that the proposed speed regulation approach achieves higher anti-disturbance capacity and precision.(3)An adaptive composite control method based on state-dependent Riccati equation(SDRE)is proposed to solve the problem of control effectiveness perturbation caused by speed switching of tail rotor or main rotor.A SDRE model to the attitude-vertical channels of variable-speed helicopter is derived and proved to be pointwise stabilizable.The designed integral SDRE baseline control law guarantees the system asymptotic stability in a large region near the equilibrium point,and an adaptive compensation law to compensate the power loss of each channel in switch phase.A finite-time disturbance observer is constructed to estimate and compensate the lumped disturbance of yawvertical channels in hover state and unswitched phase.Theoretical analysis proves that all signals in closed-loop system are uniformly-ultimately-bounded.Results of comparative simulation show that the yaw angle and vertical velocity achieve higher tracking accuracy in face of rotor speed switching and airflow disturbance.(4)Aiming at the problem of multi-source disturbances in yaw channel of smallunmanned aerial helicopter for the control mode of fixed pitch angle with speed regulation,this thesis proposes a disturbance attenuation method in the sense of a finite-gain of system.The distrubance sources include random signal noise,motor speed fluctuation,external airflow and parameter mismatch,according to the preset performance indexes,an adaptive command filtered yaw controller is designed,which consists of a virtual control function term,a filter error compensation dynamics and an estimation law to unknown aerodynamic parameters.The stability analysis results show that the closedloop system is uniformly-ultimately-bounded if without disturbance,conversely,it has the performance of-gain disturbance suppression.Comparative simulation results verify its effectiveness and advantages to attenuate the above multi-source disturbances.(5)In view of the requirements to rate limitation of yaw-vertical motion,and the fluctuation of pitch angle or speed resulting from the deviation of servo mechanism and motor outputs respectively,thus deteriorating the dynamic performance and stability.This dessertation proposes a control framework combining finite-time convergence and state constraint methods for a class of strict-feedback multiple-input-multiple-output autonomous system,and an additional dynamic in control law to resist bounded actuator fault.Theoretical analysis proves that the closed-loop system states will converge to a sphere near the origin in a finite time,and the states trajectories always remain within the predefined range.Then,a yaw-vertical controller is given based the proposed universal approach.Comparative simulation results show that it reduces the oscillation amplitude of these two channels,and the yaw angle and vertical rate always keep in the safe ranges,which still maintains good tracking performance in face of the fluctuation of pitch angle and speed.