Study On Control Strategies For Electro-hydraulic Hybrid Testing System Subject To Acceleration Vibration And Force Loading

Electro-hydraulic hybrid testing is generally employed in laboratory to simulate circumstances of the specimen subject to acceleration vibration and force loading, and it is more suitable for the mechanical property evaluation of the specimen in such compound situation compared with conventional single testing method. The crux of hybrid testing is to impose the desired acceleration and force on the specimen in parallel by electro-hydraulic control technologies, however current researches are mainly focused on single vibration or force loading methods, and the corresponding technology for hybrid testing is still immature. Hence, supported by the National Natural Science Foundation of China “Research on coordination control of super-redundant electro-hydraulic system subject to vibration and force loading” and the Jiangsu Provincial Natural Science Foundation “Research on hybrid control strategy for large-scale structure fatigue test rig”, this thesis conducts the theoretical and experimental researches for control strategies of hybrid testing technology, where the discussed object is an established uniaxial electro-hydraulic hybrid testing system. The involved theories comprise of hydrostatic transmission theory, system identification algorithm, linear control methods, and nonlinear control theory. The aim of this thesis is to form the high-accuracy acceleration and force control polices, and the results of this thesis can provide significant theoretical support and technological means for the precise control of hybrid testing systems.Firstly, the structural configuration of the discussed electro-hydraulic hybrid testing system is introduced, and then mathematical model of the hybrid testing system is established with consideration of the hydraulic nonlinearities. Moreover, based on the general control strategy for acceleration and force control system, the simulation model of the hybrid testing system is constituted, by which the dynamic behavior of the hybrid testing system are analyzed. Subsequently, a test rig for uniaxial electro-hydraulic hybrid testing system is constructed, and the test rig lays a solid foundation for the subsequent experimental researches.Secondly, to improve the acceleration tracking performance for the hybrid testing system, the parametric close-loop acceleration transfer function and its stable inverse model are obtained by system identification algorithm and the zero magnitude error tracking technology respectively, and then the feedforward inverse control strategy for acceleration control of the hybrid testing system is constituted. Moreover, an improved feedforward inverse controller is proposed with the offline designed model error corrector and furtherly this improved strategy is combined with an online adaptive controller so as to form the proposed compound acceleration control scheme. Subsequently, a series of experiments are conducted on the test rig, and the effectiveness of the proposed control strategy is validated.Thirdly, to improve the force tracking performance for the hybrid testing system, from the perspective of linear control theory, a feedforward control scheme with real-time acquired force and the control voltage of disturbance cylinder is proposed based on the structural invariance principle, which overcomes the defects of the conventional velocity feedforward controller in terms of dealing with the acceleration disturbances. Moreover, a feedforward inverse controller with disturbance observer is introduced to enhance the force replication accuracy when acceleration disturbance occurs, and then it is combined with the proposed feedforward controller to establish a novel compound force control strategy. Subsequently, comparative experiments are carried out on the test rig, and the effectiveness of the proposed controller is validated.Finally, to further enhance the force tracking accuracy of the hybrid testing system, from the perspective of nonlinear control theory, with the consideration of the nonlinearity for electro-hydraulic systems, a backstepping control strategy is recursively obtained based on the nonlinear mathematical model of the force control system. Moreover, to deal with the parameter uncertainties of the force nonlinear model, parameter uncertainties are introduced into the construction of the Lyapunov function, and then the adaptive backstepping control strategy is recursively achieved, which can online tune the uncertain parameters by the obtained adaptive updating law. Subsequently, comparative experiments are carried out on the test rig, and the effectiveness of the proposed controller is validated.