| China has a lot of energy but also with a large population. In recent years China’s economy maintained rapid growth, and has made remarkable achievements. And this achievement is accompanied in the development process of China’s huge demand for energy and consumption. At present, China has overtaken the United States to become the world’s largest energy consumer. And the CO2 emissions is 1 times higher than the United States. The contradiction between energy and environment has become increasingly prominent, which has become the main problem that restricts the sustainable development of our economy and society. In recent years, coalbed gas as a new type of clean energy has attracted many people’s attention. Coalbed gas resource in china is very abundant and gas reserves is the third of world and with broad development prospects. China United coalbed methane,Sinopec, PetroChina, Jin coal group, etc. strength of high-quality companies have invested in the development and utilization of coal-bed gas.In 2014, China’s coal bed methane extraction volume has reached 17 billion cubic meters.However, with the further expansion of the coal bed methane industry scale, the cost pressures caused by the high energy consumption of the coal bed methane extraction process has become a primary problem which restricts the sustainable development of the coalbed methane industry.In 2012, Jincheng anthracite mining group blue flame coalbed methane electricity expenses amount to 110 million yuan,become the main cost structure of the company.At present, the power supply system of coal bed gas surface mining adopts the traditional AC power supply mode. There is a "three high and low" problems of traditional AC power grid have seriously restricted the commercial development of CBM industry.And due to the instability of AC power supply system, the phenomenon of random shutdown of CBM well pumping equipment has occurred, which has brought irreversible damage to the coalbed methane wells.In order to adapt to the wide range of fluctuation characteristics of coalbed gas well load,to ensure safe and stable operation of coal seam gas exploration and research, efficient,reliable and stable,economic of coal bed methane power supply system is an effective way to ensure the sustainable development of coalbed methane industry.Chapter 1 introduces the exploitation status of coalbed methane and coal seam gas drainage safety significance, illustrate the traditional AC power supply system in CBM ground development and application of existence the question and the insufficiency, andexpounds the technical measures for energy conservation in CBM ground development power supply system to carry out the, discusses the DC micro grid power supply system research status, and the main content and significance of the study.Chapter 2 according to the deficiencies of the traditional AC power supply mode in CBM development and application at present, combined with the ground development of coal-bed gas wells multiple, wide range, geographical location complex objective conditions, analysis of the DC power supply mode compared with the traditional AC power supply mode has a unique advantage;On this basis, we discuss the CBM exploitation of DC micro grid power supply system of construction and design, the system fully consider the photovoltaic battery and other distributed energy, in energy saving also maximize the satisfaction for coal seam gas well continuous and slow drainage requirements, realize the maximization of coal layer gas well productivity,In addition, the system in the comprehensive consideration of the DC micro grid system power supply radius, line loss, electrical insulation protection requirements, based on the system cost and the design difficulty and coalbed methane DC micro network and AC power supply interface factors determined the CBM DC microgrid power supply system mother line voltage.Details of the CBM DC micro network system of PV power generation units and battery storage to the working principle of pump unit, coal seam gas load and grid interface unit, topology structure, equivalent circuit, mathematical model and control model.(The power supply system of the coal bed gas well DC micro grid is mainly composed of photovoltaic and storage battery etc.The photovoltaic power generation system is easily affected by external environmental factors,the output voltage,current and power are both unstable and random.The main load of the coal bed gas well DC micro grid power supply system is the coalbed gas pump,Its special four connecting rod mechanical motion characteristics determines the the load exhibits a cyclical fluctuation characteristics,it can be seen CBM DC micro grid power supply system from both the supply side and load side will be subjected to a large disturbance effects.Therefore, this chapter analyzes the advantages and disadvantages of DC micro grid control strategy, with the main goal of saving energy and reducing consumption,and on the premise of system stability,According to the characteristics of power fluctuation in the supply and demand of the DC micro grid system in the coal bed gas well, the layered coordinated control strategy of the DC micro grid power supply system is put forward.The micro grid system is divided into converter control layer, bus power control layer and load power balance layer.Converter control layer to achievephotovoltaic system MPPT and constant pressure control, battery storage system of the charge and discharge control, bidirectional voltage type PWM converter rectifier inverter voltage control and the system based on vector control technology of coalbed methane pumping machine speed control.The bus power balance layer is based on the relationship between the power supply and load power of the micro grid to complete the grid connected and isolated island two working states, 8 modes of switching control, in order to achieve DC bus voltage stability.Load power balance layer according to the load of multiple periodic fluctuation in micro network system,taking the minimum load fluctuation as the target,By establishing the mathematical model of load power fluctuation, based on the premise of the original operating cycle of the coalbed gas pump, the coordinated operation between the load and the load is realized by interleaving control.Chapter 3 focuses on the modeling and control of the coal bed gas pump speed control system,the exploitation of coalbed methane are generally used to reduce coal seam pressure drainage method of confined water in coal seam, so that the coal adsorption of methane released.Usually every one of the coal bed methane wells requires the technical personnel to consider the geological conditions, engineering parameters, underground pressure and other factors to develop a suitable drainage system.Drainage system directly determines the quality of the production and life of CBM,and the key lies in the control of coal bed gas pump drainage speed. Therefore, in order to make the coal bed gas well pump speed control is more effective,the dynamic modeling of the coal bed gas well pump is discussed.Based on the analysis of the kinematics, dynamics and load characteristics of the coal bed gas pump, a mathematical model of the load torque is established.On the basis of this, the application and Realization of vector control technology based on SVPWM algorithm in the speed regulation of coal bed gas pump is discussed.The load torque of the coal bed gas pump is used as the input torque of the induction motor. A vector control system model based on the synchronous rotating coordinate system(d-q coordinate system) is established.In order to lay a solid foundation for the further study of the optimal control of the speed governing system.Chapter 4 studied the optimal control strategy of the speed control system of the coal bed gas pump.The motion characteristics, dynamic characteristics and load torque analysis and modeling are mostly based on the uniform motion of the crank shaft of the coal bed gas pump. But the actual operating conditions are not so.The fluctuation of theload of the coal bed gas pumping machine often makes the running speed change.And the speed change is directly related to the size of the load torque.Therefore, how to reduce the load torque fluctuation and the system energy consumption has become a new research direction through the control of the coal bed gas pump running speed.Therefore, this chapter is aimed at the problem of high energy consumption caused by the periodic operation of the coal bed gas pump motor in electric and power generation state.The operating characteristics and load characteristics of the four bar linkage mechanism of the coal bed gas pump are analyzed through the mathematical model of the suspension point load of the pump.Put forward a new control strategy of energy saving motor, it can be achieved by variable frequency-constant frequency control.The abolition of the traditional pumping machine according to the up and down stroke divided interval running practice, the operating range of the re classified as a variable frequency and constant frequency band.According to the energy conservation law of coalbed gas is established the pump frequency conversion- constant frequency subsection control strategy model.Determined the pump variable frequency-constant frequency running demarcation point And using Runge Kutta method to solve the coal seam gas pumping machine crank angle speed value, obtain the coal seam gas pump speed optimization control curve.In the variable frequency and the control strategy change the working frequency of the motor, will pump end load potential energy is converted to kinetic energy, pumps rely on their own energy conversion operation, the motor is not acting.In the period of constant work, the motor work on the motoring condition, drive pump operation, at this time the power can be converted into mechanical energy.Effectively avoid the coal bed gas pump frequently in electric and power generation state conversion, reduce energy loss.At the same time, reducing the peak load torque, reducing the impact on the power grid, to provide a new research ideas for the stable operation of coal bed gas pumping system and energy saving and consumption reduction.Chapter 5 based on the Matlab/simulink environment, the simulation platform of the CBM pumping DC micro grid power supply system was set up,it included 10 kW photovoltaic Power System simulation model, battery energy storage system simulation model, three-phase voltage type PWM converter simulation model, CBM pumping speed control system simulation model.the layered coordination control strategy for DC micro grid of CBM well was simulated and analyzed,the converter control layer achieved the photovoltaic system MPPT, battery charging and discharging, three-phasePWM converter rectifier inverter working process,Bus power control layer based on the load and the power of the distributed power to complete the work mode switching,DC bus voltage was always stable at 600 V,the coordinated control of the load was realized by the load power balance layer,Load total power fluctuation was obviously reduced.In addition,this chapter is about the gas pump frequency conversion and constant frequency control strategy simulation program,The simulation results show that the control strategy can achieve the effective conversion of the energy of the CBM pumping in its own energy, potential energy and load side energy,The energy loss caused by the energy feedback process of the coal bed gas pump was avoided, The peak value of the load torque and the fluctuation of the CBM pumping was reduced,The impact of the system on the grid was diminished,And the stability of the system was improved,It provided an important theoretical basis and practical significance for CBM pumping with high efficiency and low consumption.Chapter 6 relying on old coal-bed gas well in Shanxi Lanyan CBM-engineering research Co.Ltd of Jincheng anthracite mining group, built CBM DC micro network experimental platform,The performance of each unit, DC micro grid system and load power balance of DC micro grid system were tested by using Fluke-435 multi function power quality analyzer;The electromagnetic slip differential speed control, common frequency control, vector control speed and the energy saving effect of coal seam gas pumping machine on Variable frequency speed control strategy of piecewise constant frequency were compared and analysed;The power indexes of DC micro grid system and AC micro grid system are evaluated;In this paper,the results show that the operation stability of DC micro grid power supply system of coal bed gas well is constructed,the vector control speed regulation system is more suitable for the periodic fluctuation load of the coal bed gas pumping,coal seam gas pumping machine on Variable frequency speed control strategy of piecewise constant frequency can effectively eliminate the energy loss in the process of negative electricity generation,Impact of load peak torque on the DC micro grid system of coal bed were reduced,In order to improve the stability of DC micro grid power supply system, a good energy saving effect has been achieved.Chapter 7 summarized the main research work of this paper, and the research direction of the DC micro grid power supply system in the future is prospected.The main innovative work of this paper is:(1)In this paper, a new energy-saving control strategy of CBM pumping motor is proposed,The practice of dividing the running range of the stroke base on up and downin the traditional pump was cancelled,The interval of running redivided into variable frequency band and constant frequency band,According to the energy conservation law,it is established the pump frequency conversion- constant frequency subsection control mathematical strategy model of coalbed gas,Determined the gas pumping operationpoint of variable frequency and constant frequency,and using the Runge Kutta method for CBM pumping unit crank angle speed value,it get CBM pumping speed optimization control curve.The control strategy can effectively avoid the frequent conversion between the electric and power generation in the CBM pumping,the the energy loss, the peak load torque, and the impact on the power grid were reduced, it provide a new research ideas and perspectives for the stable operation and energy saving and consumption reduction in CBM pumping system.(2)In this paper, based on the actual development environment of coal bed gas,using the advantages of the direct current power supply mode,the structure of the CBM DC micro network power supply system is proposed, the system not only solve the "three low and three high" problem existing in traditional AC power supply system on CBM development and application, and fully meet the requirements of the continuity and stability in coalbed methane development.(3)In this paper, the layered coordination control strategy for DC micro grid of coal bed gas well is proposed,the micro grid system was divided into converter control layer,bus power control layer and load power balance layer,each unit module control, bus voltage stability and load power optimization objective of the micro grid system were respectively realized,the control strategy can effectively improve the stability of the micro grid system and reduce the power loss of the micro grid system. |
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