Research On Low Speed Instability Mechanism And Control Strategy Of Variable Speed Pump Controlled Hydraulic Cylinder

With the development of modern industrial equipment technology in China towards precision and intelligence,the stability of the working performance of the hydraulic system,as the core component of the industrial equipment fields such as aerospace,engineering machinery and so on,is very crucial.Variable speed pump controlled hydraulic cylinder is a kind of energy-saving hydraulic transmission system developed with servo motor speed control technology.It shows strong non-linear and non-stationary characteristics due to its complex operation process,especially in the very low speed state,it often produces non-linear phenomena such as creeping,buffeting,peristalsis and so on,which causes the hydraulic equipment running in the extreme conditions to often lose stability and can’t meet the needs of some special working conditions.Therefore,the research on the mechanism of instability of variable speed pump controlled hydraulic cylinder system is the fundamental way to suppress and eliminate the phenomenon of creeping and chattering,which has important theoretical significance and engineering application value for the improvement of lowspeed performance of this type of hydraulic system.In this paper,the gear pump controlled hydraulic cylinder system driven by permanent magnet synchronous motor is taken as the research object.Based on the nonlinear dynamics theory and its research method,the instability mechanism of the system under typical working conditions is deeply analyzed,revealed the influence law of non-linear factors on the system motion behavior,and the fractional order PID(FOPID)control method is proposed to improve the low-speed operation performance of the hydraulic cylinder.The main research contents are as follows.(1)The working principle and dynamic characteristics of the variable speed gear pump controlled hydraulic cylinder are analyzed.On the basis of constructing the mathematical model of the key components of the system,a dynamic equation reflecting the global time domain characteristics of the system is established,and the low speed performance evaluation method and performance index of the system are proposed.(2)Taking the variable speed pump control hydraulic cylinder system actuator as the research object,according to the mechanical and fluid dynamics,the influence law of pump source excitation force,system damping coefficient and hydraulic oil nonlinear stiffness coefficient on actuator instability was analyzed.Through numerical simulation experiments,using typical nonlinear dynamics theory research methods,including bifurcation diagrams,time-displacement diagrams,phase trajectory diagrams and power spectrum diagrams to characterize the occurrence of actuator instability.The feasibility of the research method is verified by the existing variable speed gear pump controlled hydraulic cylinder experimental platform.(3)In order to improve the low-speed performance of the system,the mathematical model of variable speed gear pump controlled hydraulic cylinder based on FOPID controller is analyzed by using Matlab/Simulink simulation software.The results show that the FOPID controller can be used as a technical means to improve the low-speed performance of the system.The adaptive differential evolution algorithm is used to adjust and optimize the five control parameters.Finally,the effectiveness of the control strategy and method is proved by experiments.The research content provides a new idea for the instability mechanism and performance evaluation and improvement of the variable speed pump controlled hydraulic cylinder system.