Low-speed & High-torque Permanent Magnetic Motor Direct Drive System For Oil Field Workover

Workover is one of the important equipment in oil field engineering. The traditional oil field workover adopts a diesel engine or asynchronous motor as the drive. Although diesel engine can work in case there is no electricity, but diesel engine idle for a long time,which is much longer than the normal running time. Diesel engine’s work efficiency is low and the diesel engine driven system has low efficiency, high energy consumption and high pollution. The drive system of the asynchronous motor with the gearbox has low efficiency and power factor, system maintenance is complex and the noise is large. In order to solve the above problems, this paper uses the permanent magnet motor direct drive system to drive the workover. Permanent magnetic motor direct drive system has the advantages of simple structure, high efficiency and energy saving, system maintenance is simple and the noise is low. Permanent magnetic motor direct drive system can be achieved in a wide range of output torque without gearbox. As there is no reduction gearbox, motor direct drive system can make maintenance difficulty and cost significantly reduced. At the same time, the system also has the advantages of easy control and stable operation.The high speed and high torque permanent magnet motor direct drive system of oil field well repairing machine is designed in this paper. The low speed and high torque permanent magnet motor drive roller directly, gearbox is omitted, direct drive rig is realized. Workover need enough torque with wide range of speed. This paper researched the limit of field weakening control and the disadvantage of the transformation of delta winding and star winding. The wide range of constant power expansion of the motor is realized by using the transformation of single star winding and double star winding. The speed range of motor is increased to more than three times. This paper used dovetail shaped pole structure instead of conventional surface mounted pole structure. The air gap magnetic flux density waveform is optimized by non-uniform air gap rotor structure. The motors with different structure are contrasted by Ansoft, the finite element software. The air gap magnetic flux waveform and No-load EMF waveform of the different motors are analyzed. The whole control system is designed, including the design of the main circuit and the control circuit. The PLC is used as the control core, the control program of the whole system is compiled, and the main motor is controlled by the communication between PLC and frequency converter. The workover can realize the corotation, rollback, speed change and on load hover. The prototype was made. The feasibility and superiority of the system are verified by experiments in Shengli Oilfield, the workover can work normally.