Fault Diagnosis Strategy Of Permanent Magnet Synchronous Motor For Electric Vehicle Based On Search Coil

With the advantages of zero emission and no pollution,electric vehicles are increasingly favored by people.Permanent magnet synchronous motor is widely used in the field of electric vehicles due to its advantages of high efficiency and high power density,which is the main source of the vehicle power.But the complex working environment will not only lead to the occurrence of faults,but also increase the difficulty of fault diagnosis.Therefore,it is necessary to design a fault diagnosis method suitable for electric vehicles.In this paper,the three-phase permanent magnet synchronous motor is taken as the main research object.The fault diagnosis method of electric vehicle is studied according to its reliability requirements,operating condition characteristics,cost and volume constraints.The search coil is used as the detection means of fault diagnosis,which can directly detect the change of air gap magnetic field and monitor the health state of the motor more comprehensively and accurately.It has the advantages of low cost and flexible arrangement.Aiming at the fault diagnosis scene of electric vehicle electric drive system,a structural design scheme of search coil was proposed.The magnetic field variation rules of inter-turn short circuit,demagnetization and eccentricity were studied respectively,and the corresponding fault diagnosis method was designed.Aiming at the inter-turn short circuit fault,the inter-turn short circuit fault model of permanent magnet synchronous motor was established,and an inter-turn short circuit fault diagnosis method based on high frequency negative sequence component method was proposed.Firstly,because inter-turn short circuit is more sensitive to high-frequency signals,the PWM sideband harmonic signal is proposed as the fault feature to effectively solve the problem that the initial fault feature is not obvious.In the aspect of fault feature extraction,the high-frequency negative sequence components containing inter-turn short circuit fault information are separated by the reverse direction coordinate transformation.This method can suppress the influence of speed variation on diagnosis and is beneficial to the design of filter.At the same time,this method will not be disturbed by demagnetization and eccentricity faults,and the position of the fault phase can be determined by the relative change of the search coil high-frequency voltage amplitude,which provides conditions for the later fault processing.Aiming at the permanent magnet uniform irreversible demagnetization fault,a method of flux estimation based on search coil was proposed,and the degree of demagnetization of permanent magnet was judged by flux estimation.Compared with the traditional method,the influence of the resistance voltage drop on the flux estimation can be avoided because there is no current flowing through the search coil.At the same time,for permanent magnet local irreversible demagnetization fault,a diagnosis method based on the symmetrical difference of harmonic magnetic field is proposed.By using the spatial structure characteristics of the search coil,the influence of fundamental wave and third harmonic on the diagnosis is effectively suppressed,and the fault characteristic harmonics is highlighted to realize the identification of uniform demagnetization and local demagnetization fault.Aiming at static eccentricity fault,a magnetic field offset observation method based on search coil was proposed,and the offset degree of static eccentricity was judged by observing the magnetic field distribution.Aiming at dynamic eccentricity fault,the diagnosis method based on the symmetrical difference of harmonic magnetic field can effectively capture the characteristic harmonics of air gap magnetic field faults caused by rotor eccentricity.The influence of fundamental wave and third harmonic wave is eliminated,and the accuracy of fault diagnosis is improved.The influences of inter-turn short circuit,demagnetization and eccentricity on the magnetic field distribution of the motor were studied,and a comprehensive fault diagnosis method for permanent magnet synchronous motor based on search coil was proposed.Through the combination logic of fault features,multiple fault types can be identified at the same time and the comprehensive diagnosis of multiple faults can be realized.In order to provide experimental data support for fault diagnosis method,the special prototypes for fault diagnosis test were made.The fault diagnosis experiment of permanent magnet synchronous motor was carried out,which verified the feasibility of diagnosis method based on search coil.