Research On Energy-saving Design And Control Of Hydraulic Pumping Units

With the development of the global economy and the rapid growth of the world population,the consumption of energy sources is increasing.Therefore,energy saving and consumption reduction are increasingly causing people’s attention.Presently,conventional beam pumping units in oil fields are hard to realize energy recovery for the descending potential energy of the sucker rod,while their total system power is high and the overall operating efficiency is relatively lower resulting in the energy waste.But hydraulic pumping units are easy to realize energy recovery and achieve the aim of energy saving.However,present hydraulic pumping units generally have relatively complex structure and basically adopt hydraulic accumulators for energy recovery and reuse.Thus,their pumping systems need to add energy conversion components,which not only results in higher initial costs but also decreases energy recovery rate taking the efficiencies into account.Consequently,it is very significant to develop and design more energy-saving new hydraulic pumping units.The main research contents and innovative achievements in the dissertation are as follows:In Chapter 1,the features of the conventional pumping units and hydraulic ones are introduced.The hydraulic energy-saving theories and technologies are analyzed.Then,the research situation,development trend and research significance of hydraulic pumping units are discussed.Besides,the main research work of this dissertation is summarized.In Chapter 2,several new hydraulic pumping unit schemes are innovatively designed according to the operating condition parameters of existing pumping units.Firstly,two general-stroke hydraulic pumping units are designed through applying the energy-saving theory of the load-sensing technology and the double-well balance structure.Secondly,two long-stroke hydraulic pumping units are designed through utilizing the energy-saving theory of the load-sensing technology with single-well counterweight balance and adopting the energy-saving theory of the hydrostatic transmission with secondary regulation and double-well balanced structure.After parameter analysis and calculation,the results show the mechanical structures of the double-well balance or single-well counterweight balance not only can decrease system total power,but also reduce substantially the required power of the load when the sucker rod operates in the constant speed phase and make the required power very low in the decelerating phase.In addition,the double-well structure can realize continuous pumping oil and double the oil productivity.The application of the electro-hydraulic proportional load-sensing technology enables the system to adapt the load requirement in real time and change the output power as the load varies,which makes the energy-saving effect obvious.The hydrostatic transmission secondary regulation system can adjust the displacement of the secondary units in real time to adapt the load requirement.There are no throttling and overflow losses in the system,and the secondary units can recover the braking energy in the decelerating phase,which shows remarkable energy-saving effect.In Chapter 3,taking the two design schemes of applying load-sensing technology integrating with double-well balance and single-well counterweight balance as the research objects,the two systems are modeled and simulated based on the hydraulic software AMESim.Firstly,the working principle of the load-sensing system is theoretically analyzed and the dynamic models of the system components are established.Secondly,the simulation model of the load-sensing system is established and the load-sensing principle is tested in AMESim environment.Then,the simulation models of the designed hydraulic pumping unit are established.The simulation results not only validate that the pressure and flow rate of the system change as the load requirement varies,but also indicate that the system can run steadily and realize accurate control for the velocity and displacement of the sucker rods.This demonstrates the energy-saving characteristic and reasonableness of the system design.In Chapter 4,taking the hydrostatic transmission secondary regulation hydraulic pumping unit as the research object,the speed control of the sucker rod is studied.Firstly,the mathematical model of the secondary regulation system is established in MATLAB/Simulink environment,and the system is simulated based on PID control.The results indicates that the system response curves not only have larger fluctuations and overshoot during the period of parameter varying when PID controller is applied in nonlinear systems and parameter time-varying systems but also are subject to parameter variations and external disturbances when the relevant system parameters are changed.Secondly,after theories of the fuzzy control and sliding mode control are briefly introduced,sliding mode control based on fuzzy switching gain regulation is proposed and fuzzy sliding mode controller is designed.The fuzzy sliding mode control simulation model of the secondary regulation system is established and simulated.The results illustrate that the system has characteristics of steady and fast responses,stronger robustness,and better control effect than PID control.In Chapter 5,a hybrid energy-source hydraulic pumping unit based on new energy technologies is proposed.The drum of the hydraulic pumping unit is driven together by the hydrostatic transmission secondary regulation hydraulic system and a small-scale solar-wind hybrid power generation system.The rule based energy management strategy is employed,which makes the two systems and energy storage components operate according to the designed rules in different operating phases of the sucker rod.Thus,the operating efficiency of the whole system is improved.The mathematical models of the subsystems are established in MATLAB/Simulink environment and on base of this,the whole system is simulated and analyzed.The results validate the advantages of the solar-wind hybrid generation system and the energy regulation function that the batteries play,while illustrate the reasonableness and steadiness of the system design.Then,the efficiency of the secondary unit is studied experimentally on the test bench of the secondary regulation system.The results demonstrate that the overall efficiency of the secondary unit decreases as the operating pressure and the displacement factor decrease.Therefore,the correctness and effectiveness of improving the efficiency through employing the solar-wind hybrid generation system to drive the system directly in the constant speed phase are validated and the energy-saving purpose is achieved.Finally,the main conclusions and innovative achievements are summarized in Chapter 6,and further research work is prospected.