Research On Direct Drive Technology Of Low Speed High Torque Permanent Magnet Motor For Rod Pumping

The major equipment of traditional rod pumping drive device is beam pumping unit,which is based on the reciprocal motion of rod. It has many defects, such as poor performance of operating efficiency, difficulty in adjusting parameters, serious vibration noise, large occupied area, etc. Progressive cavity pump(PCP) as a new artificial lift oil production technology second only to beam pumping unit can overcome these drawbacks effectively, and it uses rotary motion of rod. But conventional PCP is driven by asynchronous motor with belt reducer and worm reduction box. There are still so many problems, such as low operating efficiency, difficulty in adjusting parameters, serious vibration noise and so on. Particularly in the case of operating PCP wells, rod string stored tremendous amount elastic energy. The energy will drive LHPMM galloping when shut in wells, and cause rod break off even accident in safety. Aiming to solve the above problems, a direct drive technology of rod string driven by low-speed high-torque permanent magnet motor(LHPMM) is studied. The transmission model of direct drive has the characteristic of low speed high torque, high efficiency and low vibration noise. Therefore, a novel surface-mounting hyperboloidal pole shoe fixed on the conventional surface-mounted permanent magnet pole is presented. In order to prevent LHPMM galloping, a new technology which consume of elastic energy stored in rod is presented. The research work of this dissertation can be summarized in the following items.Through the analysis of the problems rod pumping system, the best solution is that LHPMM drive rod string directly. By studying on the method of LHPMM design, it is found that reducing the harmonic content of the air-gap flux density can solve the problem of low efficiency effectively, and high vibration noise and so on. In order to improve air-gap flux density waveform, it is necessary to raise the sinusoidal distribution of the permanent magnet field.Conventional surface-mounted pole structure is often used by LHPMM, and form uniform air-gap. Approximately rectangular no-load air-gap flux density waveform of the traditional surface-mounted pole structure contains large harmonics. The harmonics in the air-gap causes serious torque ripple, permanent magnet eddy current loss and so on. As a result,a novel surface-mounting hyperboloidal pole shoe fixed on the conventional permanent magnet is presented.A parameterized mode of hyperboloidal pole structure LHPMM is established. Cloud genetic strategies(CGS) is used to optimize the performance of the LHPMM. Comparison simulations and tests of LHPMM with the conventional surface-mounted pole structure,surface-inset pole structure and hyperboloidal pole structure are carried out. The simulation and test results show that LHPMM with the hyperboloidal pole structure could weaken torque ripple and permanent magnet current eddy loss. The hyperboloidal pole LHPMM have better the no-load air gap flux density waveform and lower temperature rise than any other LHPMM with surface-mounted pole or surface-inset pole structure.In order to release the elastic energy stored in PCP well slowly, a elastic energy absorb device for PCP well ground drive device is designed. After analyzing the reverse principle of the PCP well, a torsional model of PCP drive system is established. The feedback energy is absorbed by PWM chopper circuit, and the motor speed is estimated by detecting zero crossing points of the back electromotive force(EMF). The effectiveness and practicability of elastic energy absorb technology are proved by simulation and experiment.