Research And Design Of Control System Of Brushless Dc Motor Used In Beam-pumping Unit

With the advantages of high working stability and simple structure,the beam-pumping unit has always been the main equipment for oil production of the oil fields at home and abroad.However,in order to overcome the big starting load,the beam-pumping unit often chooses high power asynchronous motor as the driving motor,which the designed capacity of motor is much higher than the actual value.It makes pumping unit low efficient,causing a huge waste of electricity.To solve this problem,this paper selects Brushless DC motor(BLDC)as the driving motor with high starting torque,high power factor and wide range of speed regulation,which can greatly improve the efficiency of pumping unit,to achieve the purpose of energy saving and production increasing.As the position sensor has always affected the reliability and volume of BLDC and pumping unit usually needs to work in the field,this paper adopts the sensorless control system of BLDC based on the line back electromotive force(line back-EMF)zore-crossing method to improve the ability of field operation.In addition,for the pumping unit working on periodically variable running condition,a speed control strategy based on fuzzy PI control algorithm is proposed in this paper,which can real-time adjust the parameters of the PI controller according the speed error and the rate of error change.It can reduce the effects of fluctuation of speed on the entire system,and improve the stability and reliability of the system.On the basis of the control method,this paper proposes a new method of modeling of BLDC by S function in MATLAB/Simulink environment,and verifies the correctness and feasibility of line back-EMF.What's more,the model of fuzzy PI speed controller is designed in this paper,and by comparisons of fuzzy PI controller and traditional PI control,it is proved that the fuzzy PI controller has stronger inhibitory effect on the speed fluctuation caused by periodic time-varying loads.Finally,the experiment platform of BLDC control system based on DSP has been designed and built,and the design of DSP program has also been completed.Through the experiments of sensorless control system and speed fuzzy PI control strategy,the accuracy and validity are testified by the coincidence of simulation results and experimental results.