Research On The Energy And Efficiency Characteristics Of The Variable Speed Pump-controlled Motor Hydraulic System Based On The Speed Stiffness

Due to its advantage of convenient speed regulation,compact layout,strong adaptability and large carrying capacity,variable speed pump-controlled motor hydraulic system(VSPMHS)as a typical form of the complex mechatronic transmission technology has been widely used in industrial equipment with multidisciplinary and multi-technology integration.However,due to the low efficiency of hydraulic system,unbalanced energy supply and demand,poor speed stability,complex energy coupling process,slow change of system performance with time,and uncertain system dynamic behavior under extreme conditions,the overall performance of related industrial equipment needs to be further improved.This paper takes the VSPMHS as the research object.The system dynamic behavior and energy efficiency characteristics are studied from the three levels of the nonlinear dynamics of medium,the recognize of component parameters,and the modelling of the system.Combined with the dynamic model,the power transfer,efficiency characteristics,speed stiffness and fully coupled dynamic relationship between the multi-energy domains of the system are analyzed.The model combined with speed stiffness analysis method has promotion and guiding significance for initial design of electromechanical hydraulic system,improving system energy efficiency and speed stiffness,and accurately controlling and predicting system behavior.The main research contents of this paper are as follows:The mass transfer and the stiffness of hydraulic oil during compression are described.The dynamic change law of nonlinear compression characteristics of hydraulic oil during static pressure was analyzed.Based on the bubble compression-dissolution mechanism model(Model A),and combined with the distribution law of bubbles in hydraulic oil,an improved calculation model of volume elastic modulus of static hydraulic oil(Model B)is proposed,which accurately describes the static pressure characteristics of hydraulic oil under variable pressure conditions.Furthermore,based on the Model B,the effective bulk modulus model of the flow hydraulic oil in pipeline is established for the first time.At the same time,based on the characteristics of the pressure pulsation of axial piston pump,a new online measurement method for effective bulk modulus of hydraulic oil in pipeline is proposed,which avoids the interference of online measurement on the flow stability of hydraulic oil.Considering the nonlinear compression characteristics of hydraulic oil and the mechanical-hydraulic coupling of piston hydraulic equipment,the compression loss of hydraulic equipment is re-analyzed and calculated.At the same time,for the mechanical efficiency modeling of the piston equipment,the weight coefficient of the friction state is proposed for the first time to quantify the friction state of the piston equipment.The calculation accuracy of efficiency model of axial piston equipment is improved.Combined with the improved model and experimental data,the structural and nonstructural uncertain parameters of piston pump and piston motor can be identified effectively.The data redundancy principle of uncertain parameter estimation is proposed.The non-destructive monitoring of the system can be realized by using the identified uncertainty parameters to evaluate the motion state of each pair.The operation state evaluation and quantification based on the improved model need not disassemble components and any special measurement technology.On the basis of fully understanding of the hydraulic medium working characteristics and function subsystem model,the quasi-LPV system is introduced into the dynamic modeling of hydraulic system for the first time,and the nonlinear dynamic model of VSPMHS described by multi-state space is established.The system dynamic model described in multi-state space accurately reproduces the nonlinear dynamic of the system with a wide range of speed and load changes.Under the premise of ensuring the calculation accuracy,the solution speed of the system model is greatly improved,and the inversion and prediction of the dynamic behavior of the variable speed pump-controlled motor hydraulic test bench are accurately realized.It provides reliable mechanism model support for further analysis of the system speed and energy efficiency characteristics and elimination of the uncertainty of dynamic behavior.Combined with the system dynamic model,the energy transfer and loss and the dynamic energy efficiency characteristics of the VSPMHS under steady and unsteady conditions are expounded.The optimal matching working range of the system is analyzed.The efficiency optimization scheme of the system condition adjustment and the principle of evaluating the speed characteristics are proposed.According to the characteristics of load,the static stiffness and dynamic stiffness of rotation speed are proposed to evaluate the speed characteristics of the system,and the quantification method is discussed.The influence of speed,power source characteristics and deceleration ratio on the speed stiffness of the system is further analyzed.It is pointed out that the reasonable selection of deceleration ratio according to the load characteristics can not onlu improve the static stiffness of the system speed,but also make the system load and speed work in a more efficient matching interval.Finally,the effects of interface subsystem,mechanical characteristics and load characteristics on system dynamic characteristics are analyzed.