Study On Low-speed High-torque PMSM And Its Control System For Direct Drive Oil Pumping Unit

Petroleum is one of the most important energy of human. Now, our domestic oil fields have go to the meta or later period, the characteristic of the well in our country is low liquid level deep well, viscous crude wells. Most of the pumping units have the characteristic of poor performance transmission efficiency, energy-intensive, and the motor power factor is low. They can not satisfy the need of the wells. But the control system could not resolve this contradiction. Therefore, only use direct drive structure and low-speed high-torque PMSM could significantly improve the transmission efficiency of pumping system and energy saving.The paper discusses the characteristic and design method of low speed and high torque PMSM considering driving requirement of the oil extraction system. The cause of producing pulsatile torque is analyzed, and some measures for weakening pulsatile torque are analyzed, which includes fractional slot winding, reasonable pole arc coefficient and skew stator slot. The distribution of magnetic field, waveform of magnetic filed density and pulsatile torque are caculated and simulated. These results can validate the rationality of magnetic filed pathway. The experimental results are analyzed, and these results are used to show that the method brought forward by this paper to design low speed and high torque PMSM is effective.By analyzing the actual working conditions and characteristics of direct drive structure, the control system of low-speed high-torque PMSM is designed. In order to replace PLC and other control components, the control system use programmable high performance converter. Through the test, the control system has been optimized and applied to the full balanced pumping unit.From the analysis of the direct drive screw pump unit and the techniques of oil extraction, the theory of senseless vector control is adopted. This system abort reducing mechanical and strap decelerator and increasing the reversal braking setups,which can realize functions of electrification stopping,power-off brake. Finally, the prototype and control system are installed and debugged. The low energy consumption, long stroke and low the frequency of stroke are realized. The system improves the driving efficiency by introducing a low-speed and high-torque PMSM. The result has proved that the control project is feasible and effective to extract oil effectual and scientifically, decrease energy consumption, achieve energy-saving emission reduction goals.