Research On Eccentric Fault Analysis And Detection Method Of Motor Based On Air Gap Magnetic Field

With the development of society and the progress of science and technology,traditional agriculture is also making a continuous transition to modern agriculture,centrifugal water pumps have become an indispensable part of modern agriculture.As the core of the water pump,the operating conditions of the motor will have a direct impact on the working efficiency and stability of the water pump.Rotor eccentricity is a common fault of motors,the agricultural water pump motor is more prone to eccentric failure due to the working environment,once the eccentric failure of the pump motor will affect normal agricultural production.Rotor eccentricity will change the motor air gap size and magnetic field distribution,when the air gap magnetic field changes,the radial electromagnetic force will also change,thereby producing unbalanced magnetic pulling force.The unbalanced magnetic pulling force will cause motor noise and vibration,and the motor will cause friction and even collision between the stator and rotor,which will cause hidden dangers to the safe operation of the motor and normal agricultural production.Therefore,this thesis takes the permanent magnet synchronous motor commonly used in agriculture as the research object,and focuses on the analysis of the internal magnetic field of the motor under the eccentric fault and the research on the eccentric detection method.The main contents of the thesis research are as follows:The variation characteristics of internal magnetic field and the variation law of unbalanced magnetic pulling force under static eccentric fault of permanent magnet synchronous motor are analyzed,and according to the changing characteristics of air gap magnetic field under eccentric fault,an online detection method of eccentric fault based on air gap magnetic field is proposed.The main contents are summarized as follows:(1)Theoretical derivation of the unbalanced magnetic pulling force that causes motor vibration and stator and rotor friction under eccentric faults,and use ansoft software to build the model,the finite element simulation method is used to analyze the change of the unbalanced magnetic pulling force of the permanent magnet synchronous motor under different eccentricity and different load conditions,and the change rule of the unbalanced magnetic pulling force with the degree of static eccentric failure is found;(2)The analytical method is used to theoretically analyze the air gap magnetic field of thepermanent magnet synchronous motor under normal and eccentric faults,and take the degree of eccentricity and load as variables,use finite element method to simulate and analyze the changes of the magnetic field distribution and the air gap flux density of the motor.Finally,the Fourier harmonic analysis theory is used to decompose the harmonic magnetic field in the air gap,to analyze the changes of air gap magnetic field harmonics under eccentric faults to extract fault features;(3)According to the characteristics of the air gap magnetic field change of permanent magnet synchronous motor under eccentric fault,combined with the analysis of the demand for eccentric fault detection,an eccentric fault detection scheme based on air gap magnetic field is designed,this scheme can not only diagnose the type of eccentric fault,but also determine the minimum air gap position.The system structure and testing process of the testing scheme are described,and the effectiveness of the testing scheme is verified by finite element simulation software;(4)Designed the detection device involved in the eccentric fault detection scheme,and build a motor eccentric fault detection experimental platform to verify the detection scheme and related theories.The magnetic field at the minimum and maximum positions of the air gap of the permanent magnet synchronous motor under different working conditions,different speeds and different degrees of eccentricity was tested to verify the correctness of the related research on the effect of rotor eccentricity on the air gap magnetic field.The experimental results show that: The eccentric fault detection scheme based on the air gap magnetic field designed in this thesis can not only identify the static eccentric fault and oblique eccentric fault of the motor,but also can determine the minimum air gap position when the fault occurs,and it has a high correlation with the simulation results and achieves the desired effect.