Improved Study Of PMSM Direct Torque Control Strategy In A Pump Unit

In China,most of the oil fields are low-energy and low-yielding,in which the water is pumped into the well and then the oil is pumped up from the ground by a pumping unit.The conventional pumping equipment widely used is a beam-pumping unit and the asynchronous motors are usually used as power machines.In the beam-pumping unit,there are problems such as "horse drawn cart",low power factor and high oil production cost.The permanent magnet synchronous motor(PMSM)has the inherent advantages of high efficiency,simple structures and reliable operation and it is widely used in defense,industrial control,daily life and many other fields.The performance of the pumping unit can be greatly improved by replacing the traditional asynchronous motor with the PMSM.Therefore,the control system and control strategy of the PMSM used in the pumping unit are studied in this paper.The direct torque control(DTC)strategy is adopted to control the PMSM used in the pumping unit.Firstly,the improved DTC strategy based on space vector modulation(SVM)is used.The PMSM used in the pumping unit is simulated in Matlab,the SVM-DTC can reduce the flux linkage and torque ripples effectively.According to the suspended load of the pumping unit and the weight of the main components,the formula of input torque of the main shaft of the pumping unit is derived.And the overall load characteristics of traveling beam pumping unit are analyzed.In order to solve the problem of large stator flux linkage estimation error and torque ripples in the traditional DTC,the same frequency wave observer and voltage vector calculation are improved on the basis of SVM-DTC.The SVM-DTC optimization control and discrete co-frequency filtering observation are added into PMSM-DTC system.In simulation,motor speed is set as input and pumping unit load is set as load.The feasibility and advantages of improved control strategy are verified.Finally,the hardware and software of the DTC system of the PMSM are designed.And the preliminary experimental results verify the correctness and feasibility of the hardware design.