Research On Electromagnetic Characteristics And Cogging Torque Of Permanent Magnet Synchronous Hub Motor For Vehicle

Permanent magnet synchronous motor(PMSM)has the characteristics of high efficiency,high power density and high torque density,so it has been widely used in automotive wheel hub motors and has become a research hotspot of scholars.This dissertation takes a 75 k W permanent magnet synchronous hub motor as the research object.The structure and size of the motor are designed.The principle of motor series and parallel speed regulation is discussed.The electromagnetic characteristics of different gears during operation are analyzed.The eddy current loss of the permanent magnet under different conditions are calculated.The analytical formula of cogging torque is deduced.The weakening methods of cogging torque are studied.Based on the design principle of the permanent magnet motor,according to the given performance parameters,combined with the characteristics of the hub motor,the external rotor permanent magnet synchronous hub motor is electromagnetically designed.The main dimension of the motor is calculated.The factors of the main harmonic winding coefficient and the least common multiple of the number of pole slots of the motor are taken into consideration,the choice of pole slot coordination is studied,and the winding arrangement of the fractional slot concentrated winding motor is split and designed.The magnetic circuit structure of the outer rotor permanent magnet motor is compared and determined.The electromagnetic torque and its harmonic decomposition of the motor are obtained by the finite element method.The effects of the slot width and the polar arc coefficient on the electromagnetic torque and torque ripple is analyzed.Since the hub motor studied in this dissertation needs to run in multiple gears,the method and the winding connection method of the hub motor series and parallel speed regulation are explained.Analyze the electromagnetic performance of the motor in different gear operating conditions,including the motor's no-load flux density,magnetic field line distribution,back EMF and its harmonic decomposition and load flux density,flux line distribution and electromagnetic torque.Using the finite element method,the characteristics of the eddy current density of the permanent magnet at different rotation speeds were studied respectively.The eddy current loss of each permanent magnet was calculated,and the change law of the eddy current loss of the permanent magnet at different slot to slot ratios was analyzed.Aiming at the inherent cogging torque of permanent magnet synchronous inwheel motors,the generating mechanism and influencing factors of cogging torque of in-wheel motors are analyzed,and the analytical expressions of cogging torque and related design parameters are given.The cogging torque of the hub motor when the coefficient is matched with this pole slot.The variation characteristics of cogging torque under different magnetic pole structures are explored,and the characteristic law of cogging torque when different pole arc coefficients are matched with magnetic poles of different shapes is obtained.Torque reveals the relationship between cogging torque and slot width and polar arc coefficient.