Adaptive Control Of Helicopter Structural Response Driven By Piezoelectric Stack Actuators

The high vibration levels of helicopter will seriously affect the flight performanceand the flight safety of helicopter. To effectively reduce the vibration levels of helicopterhas been the difficult problem in the field of helicopter technology which has beenexpected to solve. Active control of structural response has the advantages such as thegood control effect and strong adaptability etc., and has become the most importantdevelopment direction in helicopter vibration control. The cores of active control ofhelicopter structural response are the accurate fuselage structure/actuator couplingdynamic model, high-performance controller and actuator, requiring the controller hasthe rapid and adaptive control ability, actuator has light weight, large output force, wideworking frequency range and fast response speed. Based on the steady harmoniccharacteristics of helicopter fuselage vibration, the driving characteristics of piezoelectricstack actuators and the requirements of active vibration control of helicopter, the adaptivecontrol of helicopter structural response driven by piezoelectric stack actuators has beendeeply investigated in this thesis, and has effectively overcome the shortcomings such asthe large additional weight, the narrow range of working frequency, slow speed of control,poor adaptability etc. brought by using the inertial actuator and the controller with poorperformance in the existing active vibration control of helicopter, establishing a newmethod for adaptive control of helicopter structural response to effectively improve theperformance of active vibration control system and to effectively reduce the vibrationlevels of helicopter. This investigation has made major innovation of the following fourareas:(1) A coupling optimization method of fuselage/piezoelectric stack actuatorscomposite structure for active control of helicopter structural response has beenestablished, to solve the effect problems of installation of piezoelectric stack actuators onthe structural characteristics of fuselage and to lay a theoretical foundation forestablishing an accurate dynamic model of fuselage structure/actuators couplingstructure in the active vibration control of helicopter. Through the establishment of thecoupling frequency-domain equations of helicopter fuselage/piezoelectric stack actuators coupled composite structure and improvement of real-coded genetic algorithm,the hybrid optimization of simultaneously optimizing the discrete variables of theactuator installed positions and the continuous variables of the weighted parameters ofcontroller was achieved and the most effective vibration control was obtained in theconstraints of control input. Comparing with the current method in the world which thepiezoelectric stack actuator was idealized as a force generator, the coupling optimizationmethod can obtain the optimal results with better vibration control effect.(2) A harmonic synchronous identification-updating method for adaptive control ofhelicopter structural response has been established, to overcome the drawbacks broughtby using the discrete Fourier transform and its inverse transform for time/frequencyconversion of signals in the existing frequency-domain method in the active control ofhelicopter structural response, and lay a theoretical foundation for building thehigh-performance controller in the active vibration control system of helicopter. Usingthe recursive least squares algorithm and the steepest gradient method based adaptiveharmonic control, the identification of control error response harmonic coefficients andsynchronous updating of control input harmonic coefficients in the adaptive control ofhelicopter structural response were achieved. Based on the optimization results ofactuator installed positions and the parameters of controller, the adaptive control ofmultiple input/multiple output responses of a fuselage elastic beam model driven bypiezoelectric stack actuators by using the steady harmonic excitation and the harmonicexcitation with fast cycle time-varying amplitude has been investigated. The resultsindicated that the established harmonic synchronous identification-updating method foradaptive control of helicopter structural response could effectively reduce the vibrationlevels of helicopter, and had strong adaptive control ability.(3) An experimental control system of structural response with adaptive controlability has been set up by using the established harmonic synchronousidentification-updating method in the controller for adaptive control of helicopterstructural response. The helicopter fuselage structure was simulated a free-free elasticbeam. Using piezoelectric stack actuators to drive the beam model, taking theacceleration responses at the control points as the control objectives, the theoretical andexperimental investigations on adaptive control of the steady harmonic vibrationgenerated by the exciter simulating rotor to excite the beam and the vibration measured in a helicopter fuselage have been carried out. The results indicated that the system ofadaptive control of structural response with the controller made by the harmonicsynchronous identification-updating method and driven by piezoelectric stack actuatorscould effectively reduce the vibration level of structure, and had strong adaptive controlability.(4) A harmonic input compensation method for the hysteresis nonlinearity ofpiezoelectric stack actuator in adaptive control of structural response has been established,to solve the effect of hysteresis nonlinearity of piezoelectric stack actuator on thevibration control of structure, and to lay a theoretical foundation for building thehigh-performance actuator in the system of active vibration control of helicopter. Basedon the lower triangular characteristics of transfer function matrix of control channel, forthe single-frequency, multi-frequency vibration control, the convergence of adaptivevibration control system driven by piezoelectric stack actuator was proved and theconvergence conditions were given, and it was proved that in the presence of hysteresisnonlinearity of piezoelectric stack actuator, the linear harmonic control and the linearcontrol channel have the same convergence properties. The theoretical and experimentalstudies on the effect of hysteresis nonlinearity of piezoelectric stack actuator verified theeffectiveness of the harmonic input compensation method.