Research On Air-gap Magnetic Field Modeling And Optimization Design Of Permanent Magnet Synchronous Motor For Electrical Vehicle

In order to alleviate the increasingly serious problems of energy and environment,new energy electric vehicle has become an important trend of development in today’s automobile industry.It has been a hot point in the field of traction motor to explore Interior Permanent Magnet Synchronous Motor(IPMSM)for electric vehicle with high torque density,wide range of speed,and low vibration and noise.In this paper,taking a 25 kW IPMSM as an example,the drive motor for electrical vehicle is researched,in the aspects of modeling of air-gap magnetic field,the effects of rotor and stator structural parameters on motor performance and multi-objective optimization design,etc.The main portion of the paper is as following:(1)The design specifications of the drive motor for electrical vehicle are determined according to dynamic performance and related indicators of the electrical vehicle.The electromagnetic design is performed in terms of pole-slot combination,electromagnetic load and motor main dimensions,rotor structure and permanent magnet size,stator windings and slot shape,skewed slot,etc,thereafter,the initial design scheme of IPMSM for electrical vehicle is obtained.(2)The rotor parametric geometrical model of V-type IPMSM is created.Based on equivalent magnetic circuit method,an analytical model of open-circuit air-gap magnetic field is proposed,concerning leakage flux of rotor structure and saturation at bridge.The air-gap flux density distribution affected by the slotting is approximated by the triangular waveform and it is modified by normalized rotor pole distribution function.The value of the EMF is calculated as well.An improved analytical model of armature reaction magnetic field aimed at typical V-type IPMSM is established.The improved model,due to the consideration of the effect of bridge on rotor magnetic potential and the saturation in d-and q-axis magnetic circuit,can describe the rotor magnetic potentials in d-and q-axis more precisely.The analytical expression of the air-gap flux density distribution is deduced,and the d-and q-axis inductance is calculated as well.The validity and accuracy are verified through finite element analysis.(3)The factors that affect constant power speed range,output torque and overload capacity of IPMSM are analyzed.The 2D finite element model is established to analyze the effects of rotor and stator structural parameters on average torque,salient rate,cogging torque,torque ripple,and characteristic current of IPMSM.(4)By introducing fuzzy reasoning system,the traditional Taguchi method is improved to Fuzzy Inference Taguchi Method(FITM).The multi-objective optimal design of the motor studied in this paper is performed by FITM.FITM can solve the problem of conditionality and conflict effectively between objectives and increase the accuracy of the multi-objective optimization design.The result of optimization design shows that the motor studied in this paper meets the design requirement and has the advantages of high torque density,wide speed range and low torque ripple and cogging torque.