Research On Control Strategy Of Electromechanical Actuation Servo System For More Electric Aircraft

Driven by the demand to optimize aircraft performance,the aircraft industry's renewed push toward the concept of more electric aircraft(MEA),and ultimately an all electric aircraft.MEA is one of the main and hot research topics in the aviation field.Adoption of the electromechanical actuator(EMA)concept is seen as critical issue for the MEA to unlock significant improvements in terms of aircraft weight,fuel consumption,total life cycle costs,maintainability and aircraft reliability.In the dissertation,two kinds of high precision and high dynamic response special servo applications are the main background: the rudder actuation control system,and the electrically actuated aircraft braking system.Some related issues are studied,and the main contributions of this dissertation are as follows:In the aircraft flight control problem,the output tracking error of the aircraft servo-actuation system always has a strict limit.To overcome the shortcoming of the traditional control scheme,a barrier Lyapunov function based backstepping control is proposed in this paper.The mathematic model of the aircraft PMSM servo actuator system is established.To compensate the load disturbances and parameter variations and to eliminate the steady state error caused by the unmodeled dynamics,an integral term is introduced into the backstepping control law.A strict Lyapunov-based proof ensures that the closed loop system is global stable,the variables of the closed loop system uniformly bounded,tracking error can converge to a small neighborhood of the origin,and the tracking error remain within the constraints of the interval.The simulation results and experiment results show that the control scheme proposed has an advantage in the output tracking error constraint.Moreover,to overcome the problem of the small convergence region of the constrained variable and the knowledge of accurate model using barrier Lyapunov function backstepping control for output-constrained system,a novel robust control is proposed.By sliding mode control,the output can be driven into the convergence region when the initial output outside the convergence region,then the backstepping control using barrier Lyapunov function with integral feedback would be adopted to prevent output from violating the constraint.Simulink results validate that the control plane has the characteristics of output-constrained,fast dynamic response and the robustness to the external disturbances.Backlash nonlinearity is a common defect in electromechanical actuators installed in power-by-wire actuation systems,which may cause inaccuracies,undesired vibrations,and can even limit the systems' performances and stabilities.In order to overcome the problem of backlash phenomena,parameters time-varying and hinge moment in servo systems driven by permanent magnet synchronous motor,a backstepping-based nonsingular terminal sliding mode control strategy is proposed.The dead zone model of backlash nonlinearity can be approximated by the proposed differentiable function,the continuous state-space model of servo systems with backlash nonlinearities involved can be readily established and divided into three subsystems.In the load subsystem and mechanical subsystem,a super-twisting-based sliding mode disturbance observer is designed in order to estimate the unknown bounded disturbances,the second order sliding mode controllers driven by the disturbance observer that provide robustly asymptotic output tracking,continuous control laws are designed to ensure the auxiliary sliding variables and output tracking errors to zero in finite time.Illustrative tests are carried out.The results show that the proposed control approach is highly effective,both tracking accuracy and precise compensation of the backlash are achieved.This algorithm is the beneficial attempt to overcome the defect of backlash nonlinearity;the purpose is to keep the excellent dynamic performance of EMA.In the wheel slip control problem,conventional ABS controller is unable to maintain the braking operating point in the stable region of the tyre adhesion curve due to the nonlinear dynamics of a braking process and parameter variations.In order to overcome this problem,a backstepping sliding mode control scheme with barrier Lyapunov function has been proposed and implemented on braking systems using electromechanical actuator for aircraft.A whole nonlinear state space model with nonlinearities and uncertainties of actuator are taken into account is developed and simplified reasonably to a strict feedback form,then the equivalent description of the aircraft yaw stabilization problem can still be obtained as the problem of stabilization for output-constrained nonlinear systems with unmatched uncertainties and disturbances.Based on backstepping design,a feedback control designed with a barrier Lyapunov function to generate reference braking pressure,which guarantees the slip ratio tracking error within a pre-specified limit range without transgression of the constraints.The control law of actuator is designed using chattering free nonsingular fast terminal sliding mode to make the braking pressure tracking error converged to a small neighborhood of zero within finite time by appropriately choosing design parameters.From Lyapunov stability analysis,it is shown that asymptotic output tracking has been ensured.The effectiveness of the proposed approach is assessed on a hardware-in-the-loop experimental facility.The braking controller must be able to vary its reference slip ratio over a wide range in which unknown runway characteristics.Conventional active braking systems try to recognized current runway type online,but most of these approaches do not deliver satisfactory performance under changing runway conditions due to a priori knowledge of the friction characteristics between tyre and runway is needed.In order to overcome this problem,an extremum seeking control scheme with sliding mode has been proposed and implemented on active braking systems using electromechanical actuator for UAV.By directly estimate the gradient of friction coefficient with a extremum seeking algorithm using a modified generalized Super-Twisting,the feedback linearization controller to generate reference braking pressure from the braking pedal,which guarantees asymptotic tracking of unknown optimal slip.The control law of actuator is designed using chattering free sliding mode to make the braking pressure tracking error converged to zero within finite time based on backstepping design.Then,the convergence condition of the closed-loop system is analyzed using Lyapunov theory,and the influence of controller parameters is also discussed.The illustrative hardware-in-the-loop experimental results show that the proposed control approach is highly robust with respect to the various runway surface conditions.