Research On Waveform Reproduction Of Electro-hydraulic Servo Testing Machine Based On QFT And Adaptive Control

The electro-hydraulic servo system is non-linear and time-varying,and its adaptability to different test environment is poor,which is the main reason for the unsatisfactory accuracy of dynamic waveform reproduction of electro-hydraulic servo testing machine.In order to solve this problem,this paper presents a new control idea which combines QFT controller with adaptive inverse control on the basis of system identification by vector fitting method.Because it is impossible to obtain accurate expression of transfer function of controlled object through physical modeling in practical engineering,this paper adopts system identification method based on vector fitting method to transform ill-conditioned equations with high power coefficient of frequency into linear overdetermined equations,which can identify more accurately the expression of frequency domain of controlled object and pave the way for the design of QFT controller.The problem of time-varying of the system and its poor adaptability to different sample environments is discussed in this paper.The QFT controller and the adaptive feedforward controller based on X-filter LMS algorithm are adopted respectively from the angle of inner-loop controller design and outer-loop adaptive algorithm.Among them,QFT controller has larger bandwidth and higher control precision than PID controller,and has strong robustness to different characteristics of the test pieces,and the parameters need not be modified after tuning.The adaptive inverse control based on X-filter LMS algorithm adds an adaptive feed-forward to the inner loop QFT control,which can further improve the control accuracy of the control system and expand the bandwidth of the control system.The new algorithm can overcome the influence of time-varying on the control performance of Electro-hydraulic Servo Tester to a certain extent.Finally,an electro-hydraulic servo tester control system with fast adaptive speed,high control accuracy and good reliability is obtained.The new algorithm presented in this paper is used to simulate and reproduce various typical waveforms,in which the 30 Hz sinusoidal wave only needs 15 seconds to achieve weight convergence,and the peak error can be controlled within 1%.Triangular wave and square wave can also be reproduced with high precision by this algorithm,which is not available in many adaptive algorithms only for sinusoidal wave reproducing in engineering at present.In order to verify the application value of the new algorithm in practical engineering,taking MTS Electro-hydraulic Servo Tester as the test object,this paper compares six groups of typical experiments of force control and displacement control,including the commonly used PID control algorithm in engineering,APC adaptive algorithm in MTS tester and the new algorithm proposed in this paper.The experimental results show that the adaptive speed of the new algorithm is faster than that of APC algorithm,which can shorten the convergence time by about 90%and control the average convergence time within 6 seconds.While greatly improving the adaptive speed,the new algorithm still has high control accuracy and reliability,and can stably control the sinusoidal peak error within 1%.It has a certain application prospect in practical engineering.