Electro-hydraulic position servo system under negative load based on Lyapunov's direct method

RUAN Jun1, JIN Xiao-hong1, 2, HUANG Hao2, ZHANG Shao-feng2
(1.Key Laboratory of Metallurgical Equipment and Control Technology of Ministry of Education, Wuhan University
of Science and Technology, Wuhan 430081, China; 2.Hubei Key Laboratory of Mechanical Transmission
and Manufacturing Engineering, Wuhan University of Science and Technology, Wuhan 430081, China)

Abstract: Aiming at reducing the influence of forced flow caused by passive movement of the piston which subjected to negative load in electrohydraulic position servo system on its tracking performance, the mathematical model of the system under negative load was analyzed, and the forced flow expression was extracted. On the basis of this expression, a simple Lyapunov function based on the system's error equation was constructed by the Lyapunov direct method. The asymptotical stability condition of the system was solved through the inversion of Lyapunov direct method, and the generality of the control strategy was given. Based on the parameters of a typical electrohydraulic system, a differential control compensator in series in forward channel combine with a mechanicalhydraulic compensator with adjustable hydraulic resistance attaching to actuator were constructed with the control strategy obtained by the Lyapunov direct method, so that the control strategy proposed can be realized. The numerical simulation of this typical hydraulic system was performed by employ of Simulink software. The results indicate that, the control strategy can ensure the stability of the system under negative load, meanwhile the system can achieve the control tasks according to the displacement command signal; Under positive and negative alternating load, the system has a steady error less than 0.183%, and the adjustment time is less than 0.02 seconds.
Key words: negative load; electro-hydraulic position control system; Lyapunov direct method; mechanical-hydraulic compensator