Research On Bldcm Control System For Pumping Unit Direct Drive

There is a statement thaf“getting petroleum at the cost of electrical energy”in the world petroleum producing process.Waste of energy plays an important role in the cost.Sucker rod oil pumping is primary method in all these artificial pumping metheods presently.In the facility of sucker rod pumping,beam-pumping unit is applied widely.A new scheme of pumping unit directly drived by commutating Brushless DC Motor is presented in this paper for some shortcomings of beam-pumping unit,such as long driving chain,poor flexibility,tremendous cubic and weight in long stroke,and low efficiency.The changing law of suspension center load with the stroke position is analyzed according to the stress characteristics of sucker rod oil pumping system in this paper.Moreover,based on the above,control system of commutating pumping unit directly drived by Brushless DC Motor is designed for the first time,replacing the conventional induction-retarder structure with BLDCM. Building block design is adopted throughout the overall structure such that the pumping unit directly drived by commutating Brushless DC Motor has more extensive compatibility and controllability.The stroke and the frequency of stroke can be adjusted conveniently.In order to improve the system efficiency,the motor pushing force is designed to be matched to the suspension center load.Such scheme is in agreement to the trend of longer stroke and lower frequency of stroke in the stem-oil pumping system.The overall system is a single loop system which implements the function of current limiting and closed-loop speed control.Current limiting is implemented by molectron,and speed control is implemented by molectron and simple integral circuit.The three-phase windings of stator are powered by threephase rectifier circuit,the state of six power tubes of which are controlled by six kinds of states generated by three Hall position sensors.The decoder and driving circuit of power tubes are implemented by IC.The model of BLDCM is established by Matlab/ Simulink.According to the real composition and function of the system,the models of motor and trigger logic of power tubes are established completly by modules,they can be transplanted and extended easilyAccording to the actual direction requirement of commutating BLDCM,the model of control system can implement forward and reverse revolution.A model,which can simulates the load torque of different stage,is established based on the analysis of motion rule and load of suspension center.It can simulate the real working state of pumping unit directly drived by commutating Brushless DC Motor.Comparing the new pumpimg unit system with the traditional beam-pumping unit system and analyzing their efficiency individually,we made a conclusion that the new one has higher efficiency.New pumping unit system designed in this paper,which cancel retarder and four bar linkage mechanism and shorten the force transmission step from motor to pumpimg rod.The maladies in convertional beam pumping unit such as long transmission chain,poor controllability and low efficiency are overcome.A new method which solves ultimately high energy waste in oil field is presented.Feasibility and effectivity are verified in this paper as well.