The Analysis And Research Of Submersible Motor Terminal Overvoltage

As one of the important mechanical furnishment in the exploitation of the oil-field, submersible motors have been used widely and become one of the major means in the oil-field production.Submersible motors technology have the strongpoints of taking fewer expoiting area, constructing simplily and high efficient exploitation.But at the same time , submersible motors have a series of disadvantages when runing at usual frequency .Such as taking a great start current,a serious mechanism impact damage to the pump ,and can't control the flux and work state according to the change of the liquid surface automatically.So many submersible motors have to be controlled by variable-frequency technology.The submersible motor's performance has been matched to the throughput of the oil well adequately by the application of the conversion power supply, so the efficiency of the submersible electrical pump has been increased greatly. At the same time, a series of negative problems have been brought by the application of the variable-frequency source. The submersible motor works 1000-3000 meters in the oil well underground,so it needs a long cable to supply eletricity, when adopt PWM(Pluse width module) to control the motor, the output voltage of PWM will go up and down quickly which is dv/dt has a rapid transform.Because of the cable have inductance and capacitance,so when the incoordination of characteristic impedance for the cable and load, bringing to reflected wave of voltage, producting a great terminal over-voltage which will make the insulation of cable and motor breakdown and damange.Space vector pluse width module has the characteristics of high utilization of DC,good dynamic performance,and easy to realize by digital technology .And have been used widely.This paper adopt SVPWM to control the submersible motor's variable-frequency,base on MATLAB/Simulink to bulid a control sysem's simulink model,buliding the models of submersible motor's control sysem which is supplied by SVPWM-inverter.On the basic of model, the theoretics analysis and the emulation research of overvoltage have been done in this thesis. The incoordination of characteristic impedance for the cable and the motor will lead to the terminal overvoltage, and the magnitude of the overvoltage and the concussion frequency will increase with the increasement of cable's length.A filter is fixed after the inverter,and the simulink indicates it can restrain over-voltage efficiencily.Through the analysis and research of this paper, some techniques can eliminate or minify the adverse influence, so the submersible motor's efficiency can reach the highest point when it uses conversion power supply.