Research On Energy Management Strategy Of Hydraulic Lifting System Actuated By Composite Cylinder Based On Prime Mover Work Point Adjustment

Hydraulic lifting system is widely used in engineering,such as robotic arm driving system in hydraulic excavator and pumping system in hydraulic pumping unit.The hydraulic lifting systems usually work for a long period of time under the working conditions with heavy load.The energy consumed occupies most of the energy consumption of the whole machine.However,the traditional hydraulic lifting systems have low energy recovery efficiency and large load fluctuation,which makes it difficult for the prime mover working point to remain in the high efficiency zone.This results in a large energy loss during the working process and an increase in operating costs.Therefore,the high-efficiency energy recovery system is used to recover the braking kinetic energy and gravitational potential energy of the hydraulic lifting system.Also,the energy management strategy of the hydraulic lifting system is developed to improve the working point of the prime mover,which become an effective measure for energy saving.Most of the existing hydraulic lifting systems have the energy recovery capability,which has a certain energy saving effect,but there is still some room for improvement.In this pape'r,the hydraulic lifting system is taken as the research object.Research work around the structure,characteristics and energy management strategies of the system is carries out.In the paper,the principle of hydraulic lifting system with composite cylinder as actuator is discussed,the mathematical model of hydraulic lifting system is established,the dynamic characteristics and energy recovery efficiency of the system is analyzed,and the parameter matching method is proposed.Taking the hydraulic excavator and hydraulic pumping unit as an example,the load characteristics of the hydraulic lifting system are analyzed,and the method of predicting the load of the prime mover is studied.Based on the load forecasting,the instantaneous optimization energy management strategy,the dynamic programming energy management strategy and the fuzzy control energy management strategy based on genetic algorithm optimization are proposed.The efficiency of the hydraulic lifting system is improved by adjusting the prime mover working point.The effectiveness of the energy management strategy was compared by simulation analysis and experimental verification,and the applicable conditions of each energy management strategy were discussed.The main contents of the dissertation are presented as follows:Chapter 1 outlines the composition and characteristics of the hydraulic lifting system,describes the research progress of the hydraulic lifting system and its energy management strategy applied to engineering machinery and petroleum machinery,and summarizes the development of hydraulic lifting system structure and energy management strategy.In the direction,the research background and research significance of this topic are analyzed,and the main research contents of this topic are introduced.Chapter 2 explores a hydraulic lifting system based on a composite cylinder.The system utilizes composite hydraulic cylinders and accumulators to recover actuator and load potential energy in the form of pressure energy,avoiding loss of energy conversion process;using closed pump control system to reduce loss of energy transfer process;designing auxiliary drive system to adjust the prime mover's work point,which in turn improves the efficiency of the prime mover.The mathematical model of each component of the hydraulic lifting system is established,and the simulation model is obtained accordingly.Chapter 3 presents a parameter matching method based on system dynamics and energy recovery efficiency.The dynamic characteristics and energy recovery efficiency of the hydraulic lifting system under different composite hydraulic cylinder diameters and accumulator volume are obtained by simulation analysis.Increasing the composite hydraulic cylinder diameter can improve the dynamic response of the system,but it affects the stability of the system.The energy capacity of the device can enhance the stability of the system,but the dynamic response of the system deteriorates.Reasonably increasing the composite hydraulic cylinder diameter and accumulator volume can generally reduce the maximum output power of the prime mover to a certain extent and reduce the energy consumption of the prime mover.On the basis of parameter matching,hydraulic excavator and hydraulic pumping unit are taken as examples,and the energy saving effect of the hydraulic lifting system under their typical working conditions is obtained by simulation analysis.From the simulation results,the energy recovery system can significantly reduce the maximum working pressure of the hydraulic lifting system,the maximum output power and energy consumption of the prime mover.Chapter 4 studies a load forecasting method for hydraulic lift systems based on neural network algorithm.For the uncertain load of the hydraulic lifting system,the pump inlet and outlet pressure difference and control signal are selected as the identification parameters of the working stage,and the neural network algorithm is used to obtain the action during the hydraulic lifting system operation,and then the working stage is identified.The cycle of operation process is truncated according to the result of work phase identification.The cubic spline interpolation function is used to obtain the torque curve of the prime mover in the first few cycles,and the predicted load of the next working cycle is obtained by superposition.Taking the hydraulic excavator as an example,the AMESim simulation model of the hydraulic excavator lifting system was established.The parameters of the prime mover torque,power and hydraulic system pressure during the working process were obtained and the load was predicted.According to the cross-correlation analysis,the predicted load is highly correlated with the actual load,and the prediction is more accurate.Finally,the feasibility of load prediction is verified by experiments.Chapter 5 analyzes the energy management strategies based on the prime mover's work point adjustment,including instantaneous optimization energy management strategy,dynamic programming energy management strategy and fuzzy control energy management strategy based on genetic algorithm optimization,and proposes fuzzy control energy based on genetic algorithm optimization.Management stratesgies have better energy savings.Continue to use hydraulic excavators and hydraulic pumping units as examples to simulate and analyze the above three energy management strategies.Through comparative analysis,it can be seen that the three energy management strategies can adjust the working point of the prime mover to make it more concentrated in the high efficiency zone,thereby improving the efficiency of the hydraulic lifting system.The instantaneous optimization energy management strategy has better control effect on the maximum output torque of the prime mover,but the average efficiency of the prime mover and the overall efficiency of the system are not improved much.The strategy has the least amount of calculation and does not need to predict the load.It is suitable for real-time control of the hydraulic lifting system.The dynamic planning energy management strategy can reduce the energy consumption of the prime mover and obtain higher system efficiency,but the calculation is the most.And it has the strongest dependence on the accuracy of load prediction.Although it has better energy-saving characteristics,it has a greater limitation on real-time control.The efficiency of fuzzy control energy management strategy based on genetic algorithm optimization is between the above two.The strategy optimizes the fuzzy algorithm by using the predicted load,and has strong adaptability to different working conditions.At the same time,the accuracy of the load prediction result is lower,and the system efficiency is better than the instantaneous optimized energy management strategy.The fuzzy control energy management strategy based on genetic algorithm optimization is more suitable for hydraulic lifting system.Chapter 6 summarizes the research work of this thesis,summarizes the main conclusions and innovations of this thesis,and looks forward to the next research direction and research content.