Study On The Working Characteristics And Control Strategy Of Parallel Digital Hydraulic Transformer

The traditional hydraulic system has the disadvantages of high energy consumption and low efficiency,which greatly affects its further application and development.The emergence of constant pressure network secondary regulation system has changed this situation.Because of its advantages of high efficiency and energy saving,it has become a research hotspot in the field of hydraulic transmission.The hydraulic transformer is the core control element of the system,which can control the actuator without throttle loss and can recover the energy of the load end.In this paper,a Parallel Digital Hydraulic Transformer(PDHT)is proposed,which is composed of four pump/motor units with binary displacement code and a control valve group.By changing the switch state of the control valve group,the displacement ratio is adjusted,and then the pressure is adjusted.On the basis of exploring the working characteristics of PDHT,this paper formulates its control strategy for hydraulic cylinder.Firstly,based on the working principle and structure of PDHT,the mathematical models of PDHT displacement,flow,torque and efficiency were established,and the PDHT simulation model was built in AMESim to provide a basis for subsequent research.Secondly,according to the law of displacement ratio,the working characteristics of PDHT are further analyzed,and the pressure,variable pressure ratio,flow rate,torque,speed and efficiency of PDHT under different displacement ratios and the same displacement ratio are studied.On this basis,the forward pressure regulation and reverse energy recovery process of PDHT are analyzed,and the discriminant index of displacement ratio regulation is determined,which lays the foundation for the development of PDHT control strategy.Then,the PDHT is applied to the constant pressure network,and the hydraulic cylinder control system based on PDHT is designed,which has drive mode and energy recovery mode.In order to achieve the different control objectives of the two modes,the control strategy based on pressure shift is proposed,which mainly includes three aspects: gear formulation,shift rules and shift strategy.AMESim simulation results show that the control strategy based on pressure shift can achieve the control objectives of the system.Finally,a test platform based on PDHT hydraulic cylinder control system was built to verify the working characteristics and gear test.On this basis,the driving mode experiment of the system was carried out.The experimental results show that the control strategy based on pressure shift can make the system adapt to load changes and run efficiently and smoothly.