Analysis On Characteristic About Doubly Salient Electro-magnetic Wheel-hub Motor Used For Electric-vehicle Driving System

The Doubly Salient Motor(DSM),credited with the advantages of simple structure,strong reliability,high power density and high temperature resistance,four quadrant operation and so on,is suitable for speed-regulated applications.However,the salient pole and slot structure contribute to high torque ripple and serious nonlinear magnetic field distribution,which make it difficult to analyze.Moreover,it brings technical problems in the design and application of doubly salient motor.This paper is based on present achievements of DSM and develops a 12/8-pole external rotor Doubly Salient Electro-Magnet(DSEM)for electric vehicle driving system.First,the application of DSM to electric vehicle driving system and the research of it both abroad and at home are introduced.Then,operating principle and mathematical model of DSEM is elaborated respectively.Moreover,based on the linearization of excitation flux,some control strategies are put forward and analyzed,such as the three-phase three-state(TPTS),three-phase six-state(TPSS)and so on,which is the foundation for further research upon DSEM.Considering the chosen of structure,size and pole arc coefficient,a 12/8-pole external rotor DSEM applied to electric vehicle driving system is designed.Then,finite element method(FEM)is applied to analyze magnetic field.A series of static characteristics are investigated,such as air gap magnetic density,field flux,inductance and armature reaction.Based on the static characteristics,steady characteristics of the motor,such as phase current,field flux and output torque are studied.Different control strategies are compared and analyzed,which provide references for the application of DSEM.Based on FEM,the influence of rotor width,air gap length,yoke thickness and core length on the static and steady-state characteristics is studied in detail,which provides a meaningful reference for the rational design of motor.Finally,the final optimized structure of the 12/8-pole external rotor DSEM is given.At the same time,an inner rotor DSEM with the same size is designed,and the performance of them is compared and analyzed.