Research On The Control System Of Brushless Double-fed Direct-drive Screw Pump

In recent years,brushless doubly-fed motors have received more and more attention due to high reliability,flexible control scheme,and adjustable power factor.Besides,brushless doubly-fed motors have important application potential in many fields such as wind power and hydropower.With the rapid development of technology,the economic demand for energy is increasing,and oil is an indispensable part of energy.The screw pump gradually replaces the traditional oil extraction equipment by its advantages such as stable liquid discharge and high efficiency.For the current screw pump drive system,to solve the inefficiency of the asynchronous motor and the braking and demagnetization of the permanent magnet motor,based on the application of brushless doubly-fed motors in the oil extraction industry,this article proposes a new type of brushless doubly-fed direct-drive screw pump oil extraction system,and focuses on the following aspects:First,the article discusses the research background of oil extraction equipment and points out the development trend and existing problems of the screw pump direct drive oil production system.At the same time,the research history of brushless doubly-fed motors are sorted out.After introducing the working principle of brushless doubly-fed motors,a mathematical model of brushless doubly-fed motors in the three-phase static coordinate system and rotor speed coordinate system are established.On the basis of the improvement of the performance of the brushless doubly-fed motor,the operation mechanism of the AC frequency conversion phase advancer is introduced and its mathematical model is established.Based on the feature of adjustable power factor of the brushless doubly-fed motor,the excitation mechanism and the excitation magnetic potential distribution of the brushless doubly-fed direct drive system is analyzed,and the phase advancer is introduced for the brushless doubly-fed direct drive system to realize reactive power compensation.Secondly,based on the characteristics of high efficiency of low-frequency AC excitation and spatial sinusoidal distribution of AC winding magnetomotive force,this paper proposes a low-frequency excitation operation mode and system topology of the brushless doubly-fed motor based on dual-port variable frequency control.At the same time,the power winding voltage-oriented vector control strategy is adopted to realize the control of reactive power and electromagnetic torque on the basis of vector decoupling.The excitation control strategy is adopted for the phase advancer on the control winding side,and the dynamic and steady-state characteristics and efficiency performance of the brushless double-fed direct drive system are analyzed based on the simulation results.Thirdly,the software and hardware structure of the brushless double-fed direct drive system is designed,including the electrical wiring and control program of the system.The program is used to set the switching cycle to solve the overcurrent problem when the phase advancer commutation.In order to improve the reliability of the system hardware,protection mechanisms such as overvoltage and overcurrent are set for the motor.Finally,this paper builds an experimental platform based on the topology of the brushless double-fed direct drive system.Through the load and speed regulation experiment of the direct drive system,the response performance and stability of the brushless doubly-fed direct drive system to changes in load and speed are verified;Through the reactive power compensation experiment on the direct drive system,the effectiveness of the phase advancer for the reactive power compensation of the brushless double-fed direct drive system has been verified;Through direct drive system efficiency experiment,motor temperature rise experiment and braking experiment,the system's high-efficiency,reliable performance and practical application feasibility are further verified.