Precise Control Of Valve-Controlled Electro-Hydraulic Servo System In Wind Tunnel

Electro-hydraulic system characterizes high power output, high rigidity,compact structure and being stepless velocity easily, combining the advantages ofelectric and hydraulic. It is widely used in wind tunnel beaucse of being suited to bigload mass and quick response of the regulating mechanism. The electro-hydraulicposition control system which is the type of valve controlled asymmetrical cylinderis popular in wind tunnel, such as the different structural model supporting system.Because the extension and retraction of piston is asymmetrical and part ofsystem parameters are indefinite, it is difficult to build the full and precisemathematical model of the vavle controlled asymmetrical cylinder electro-hydraulicposition control system. Meanwhile, it is unreal to meet the requirement of widespeed range, high position and speed control accuracy of electro-hydraulic system ofmodel support in wind tunnel, using a single servovalve by the PID control method.Aiming at the above question, this paper synthesizes theoretical analysis, digitalsimulation and experiment method. It contains six chapters all together and thecontent of every chapter is introduced as follows.In the preface of the thesis, we briefly introduce the principle, constitution, sortof electro-hydraulic control system and electro-hydraulic servovavle firstly. Then wegive a review about the characteristic of typical electro-hydraulic position system inwind tunnel and problems in control. At last, we present the research backgroundand the work of this paper.In the second chapter, a more precise mathematical model of the valvecontrolled asymmetrical cylinder electeo-hydraulic position control system ispresented. We deduce the model of two inverse directional motion, considering theasymmetry of piston area. Based on the principle of energy conservation law, theload pressure and load flow rate is defined again. The initial position and totalvolume of asymmetrical cylinder are analysed by applying the theory of hydraulicspring stiffness when its natural frequency is minimum. Combining the model ofelectric control system, transfer function of the full electro-hydraulic position servosystem is presented. At last, considering some specific system, the transfer functionof every section is given.In the third chapter, we briefly introduce the hydraulic simulation technologyand the frequently-used simulation software MATLAB/Simulink and AMESimfirstly. Then we make modeling and simulation research considering the electro-hydraulic position servo system mentioned in the second chapter, usingSimulink and AMESim respectively, and compare the advantages and disadvantagesof each other. At last, applying the interface technology of AMESim and Simulinkwhich makes the best of the both software, we build the united simulation model ofthe same system.In the fourth chapter, a compound control strategy with speed feedforward andposition feedback is presented, aiming at the difficulty of the nonlinear velocity’accurate control of cylinder. To meet the requirement of wide speed range and highposition control accuracy in the electrol hydraulic-system of model support in windtunnel, a control scheme about the small flow rate zero lap servovalve and the bigflow rate positive lap servovalve in parallel is proposed. Meanwhile, to study thefeasibility of the proposed control method, we make simulation research aboutelectro-hydraulic position servo system of a single servovalve controlled cylinderand two servovalves in parallel controlled cylinder using AMESim.In the fifth chapter, we put up the two servovalves in parallel electro-hydraulicservo system test platform and perform correlative experiment research based on NIembedded real time control system. The simulation and experimental results showthat the positon and speed of the cylinder can be controlled simultaneously with thetechnology of two servovalves in parallel and velocity and position hybrid control.At the last chapter, a review about the work in the thesis was made, the shortageof the work and the direction about the future research are presented.