Research On Modular Combined Permanent Magnet Motor For Direct Drive Of Submersible Screw Pump

The submersible oil production system can exploit horizontal wells and inclined wells,which is very suitable for the current development of my country's oilfields.Currently,the system is driven by an asynchronous motor and a reducer,and there is a problem of high failure rate.This limits the development of my country's oil exploration.This paper proposes a modular combined submersible motor based on the structure and design defects of the traditional submersible motor,analyzes the characteristics of the combination of large-span winding modules and the combination of de-coiling modules,and chooses the method of de-coiling and optimizes the pole slot coordination.This design significantly reduces the yoke space,increases the diameter of the air gap circle,improves the torque density of the motor,and makes the submersible motor more applicable.On this basis,the cogging torque,back-EMF harmonics and torque ripple are analyzed.Aiming at the problem of small radial size of the motor,small permanent magnet size and large magnetic leakage,a structure with built-in tangential permanent magnet with radial compensation is proposed.This structure significantly reduces the magnetic flux leakage of the motor and improves the magnetic load and torque density of the motor.The submersible permanent magnet motor works thousands of meters underground,and the high temperature and high pressure environment seriously affects the service life of the motor.Traditional uphole temperature rise experiments are also difficult to simulate downhole conditions,so the temperature rise estimation of each part of MCSPMM is the top priority for material selection and motor reliability.In this paper,the method of calculating the equivalent Reynolds number is used to simplify the heat convection into heat conduction,and then the finite element calculation of the three-dimensional temperature field of the motor is carried out and the temperature rise distribution of each part is obtained.Based on this,the design reference basis of MCSPMM is summarized,which has a certain reference significance for future research.The armature magnetomotive force generated by the fractional slot concentrated winding contains more low-order harmonics,which may cause more serious vibration problems,which is vital to the stable operation of the motor.In this paper,Maxwell stress method is used to obtain the components of the radial force wave of the conventional submersible motor and the modular combined submersible motor,and a detailed analysis is carried out according to the source of the radial force wave.And further compare its harmonic content to summarize the general law for the permanent magnet motor radial force wave.With the help of commercial finite element software,the electromagnetic force is applied to the stator to analyze the modal and harmonic response of the conventional motor and modular combined stator,and then analyze the influence of the modular combined stator on the motor vibration.It can be seen that low-order radial force waves have a greater impact on vibration,and the stiffness of the motor's stator is lower after the module is combined.Special attention should be paid to the influence of low-order radial forces when designing.