Design Of Position Sensorless Control System For Brushless DC Motors Used In Progre Ssing Cavity Pump

Oil is a non-renewable resource，with being over exploited year by year, thereserves have been reduced rapidly and the oil exploitation has to turn to oilfieldwhich is hypotonic and full of viscous oil and sands, the difficulty of exploitation isincreasing so that the traditional mode of exploitation has been difficult to adapt tothe working environment. The direct driving submersible progressing cavity pump isdone by the submersible motor through speed reducer direct to drive, it has theadvantages of simple structure, low energy consumption, high efficiency, and goodperformance of sand-carrying.Permanent magnet brushless DC motor has comparable speed regulating to DCmotor. It is used as the submersible progressing cavity pump’s driving motor, basedon the three harmonic detection method, it takes the sensorless control method,reducing the volume of the motor greatly, and at the same time making the rotorposition signal more stable, so it is particularly suitable for submersible workingsystem.Firstly in this dissertation the basic principles of BLDC were introduced, itscontrol method with a mathematical model was analyzed. According to thecharacteristics of the submersible screw pump’s small working space, harshenvironment and strong interference, the third harmonic of back-EMF zero crossingdetection method was used to obtain the rotor position information, and sensorlesssubmersible screw controlling system was designed, too, phase delay generated bythe back-EMF third harmonic filter circuit was analyzed, the corresponding phasecompensation measures was designed to make the motor can change phase correctly.The Buck converter was joined in the main circuit, the attack of high-frequencyharmonic circuit to the before and after circuits was filter out in the inverting process.Secondly, the speed and current double closed-circle PI regulating velocitysystem was designed and simulation model system was built by use of the MATLABsoftware. The waves of electromagnetic torque, speed, stator current, induction voltage and harmonic voltage were obtained. And these waves could verify thefeasibility of the method and could provide favorable basis for the system predevelopmentThirdly, in view of the simulating verification of the system design scheme, thisdissertation designed the system hardware circuit which used the digital signalprocessor TMS320F2812of TI company as the core. This hardware circuit includedagainst EMF detection circuit, filter circuit, AD conversion circuit, status displayingcircuit, voltage and current sampling circuit etc. and also designed the PCB board ofthis hardware circuit and completed the welding.Finally, the software of the control system was designed using C-language.Through several times of testing and debugging, the motor can run stably, and itsparameters tested are consistent with simulation parameters, the software designedabove can achieve the ideal results expected, at the same time the validity of thedesign scheme was verified.