Research On Mechanism And Suppression Method Of Speed Fluctuation In Variable Speed Pump-controlled Motor System

With the continuous improvement of hydraulic transmission technology,hydraulic equipment is developing in the direction of large-scale,high-speed,high-pressure and intelligence.Due to the special structure of hydraulic equipment and working conditions,the dynamic information of hydraulic equipment is affected by various complex coupling effects and non-linear factors in the transmission process.The traditional signal sources such as pressure,flow,vibration and noise cannot guarantee the objectivity and integrity of information in the operation state of multi-energy-domain coupled hydraulic system;moreover,the traditional signal processing method is strong.Under the influence of coupling and big noise,it is difficult to realize feature separation.Speed fluctuation analysis is an effective performance evaluation and fault diagnosis method used in the field of rotating machinery,which can well reveal the operation state and fault evolution mechanism of various rotating equipment.The instantaneous speed fluctuation generated by the hydraulic system will have a great impact on the safety of equipment operation and system performance.The mechanism and suppression method of hydraulic pump and motor speed fluctuation in large equipment has become a research hotspot in the field.In this paper,the variable speed pump-controlled motor system is taken as the research object,the mechanism of speed fluctuation of plunger equipment(pump/motor)is analyzed,the simulation model of variable speed pump-controlled motor hydraulic system is built by using AMESim,and the influence mechanism of different oil physical parameters and environmental conditions on pump source speed fluctuation is studied,and the pump source speed fluctuation of pump-controlled motor system is also studied.The suppression method is studied,which provides theoretical basis and technical means for the study of hydraulic system control strategy and performance optimization.The main works accomplished in this paper are as follows:(1)The mechanism of speed fluctuation in variable speed pump-controlled motor hydraulic system is studied.According to the working principle of pump-controlled motor hydraulic system,the full-coupling dynamics model of plunger equipment(pump and motor)is solved,and the mechanism of pump end speed fluctuation in hydraulic system is analyzed theoretically.The main influencing factors include the structure parameters of equipment,load pressure,input torque,oil and liquid properties,etc.(2)The whole simulation model of pump-controlled motor hydraulic system is established by using AMESim simulation software.Based on the structure and working principle of the plunger equipment,the simulation models of Linde HPV-55 axial plunger pump and Linde HMV-105 axial plunger motor are established respectively.According to the working principle of closed hydraulic system,the closed hydraulic system model was built.In the process of modeling,the influence mechanism of oil properties and leakage on the speed fluctuation of pump source is fully considered.Through the experimental results and comparative analysis,it can be concluded that with the increase of the rotational speed,the fluctuation of the pump source speed will increase significantly;with the increase of pressure,the fluctuation of the speed will decrease significantly,which verifies the validity of the model.Based on the simulation model,the effect mechanism of oil temperature,gas content and viscosity on pump speed fluctuation is analyzed.The results show that with the increase of oil temperature,the fluctuation degree of pump end speed increases;with the increase of oil gas content,the fluctuation trend of speed first decreases and then increases,ranging from 0.01% to 0.18% and from 0.18% to 0.51% respectively;with the increase of oil viscosity,the fluctuation degree of hydraulic pump speed increases.Both the amplitude and the speed fluctuation rate decrease.(3)The feature extraction method of piston pump speed fluctuation signal is studied.In engineering practice,there is a coupling effect between noise and oil fluctuation in hydraulic system,which makes the instantaneous speed signal extremely complex.Therefore,the signal processing method based on zero phase order filter can successfully extract the characteristic signal of speed fluctuation and its order spectrum,and provide methodological support for evaluating the control strategy and performance of variable speed pump-controlled motor system based on speed fluctuation.(4)The effect of the factors such as accumulator inflation pressure,volume and load moment of inertia on the speed fluctuation of pump source is studied experimentally under different working conditions.The results show that under different working conditions,with the increase of accumulator inflation pressure,the cushioning effect of hydraulic system will increase and the speed fluctuation of pump source will decrease obviously;and with the increase of accumulator volume,the pump source will decrease obviously.The fluctuation of pump speed will decrease first and then increase,and the fluctuation of pump source speed will decrease with the increase of load inertia under different rotational speeds and load pressures.Through the research,we know the relevant parameters of restraining the fluctuation of pump speed in the hydraulic system,which provides a theoretical basis for the structural optimization design of the system and the safe operation of the system.