Design And Analysis Of High Torque Density Permanent Magnet Motors For Electric Vehicles

With the rapid increase of the number of cars,the environmental pollution is becoming increasingly serious and the dependence of foreign oil keeps increasing.The energy crisis and environmental pollution have become the two major problems faced by our country.Compared with the traditional fuel car,the electric vehicle has become a research hotspot because of its low emission.Therefore,China has also launched a series of policies and measures to promote the development of the electric vehicle industry.As the core component of electric vehicle driving system,driving motor needs to meet the requirements of high overload capacity,wide speed range and high efficiency.Permanent magnet synchronous motor(PMSM)is becoming the main choice for its good performance.This paper designs a PMSM for the electric car,optimizes it to obtain high torque density performance and analyzes its mechanical strength and efficiency.First of all,according to the parameters and dynamic requirements of the electric car,the paper obtains the requests of driving system and determined the motor 's output characteristics.Based on the target of high torque density,the motor's overall structure is selected,including the pole's and solt's number,stator slot structure and permanent magnet arrangement.The electromagnetic load prefetching method is used to calculate the inner diameter and axial length of the stator,and the other main parameters are designed and calculated.Secondly,based on the simplified model of the permanent magnet synchronous motor,the electromagnetic torque of the motor is analyzed.The influence of each part on the average torque and the torque fluctuation is studied,and the torque caused by the harmonic is deduced.Based on the designed and calculated parameters,the paper establishes the two-dimensional model of the motor.The no-load simulation analysis and load simulation analysis of the model are carried out,and the torque performance of the motor is obtained,which is conformed to the analysis.Thirdly,the stator parameters and rotor parameters which affect the torque performance are selected for parametric analysis respectively,and the influence of the variation of each parameter is studied.According to the analysis results,the paper selects the optimal range of every parameter and optimizes all parameters synthetically using the multi-objective genetic algorithm in the finite element software.Then,the paper selects a solution as the optimization result.By comparing the output torque before and after optimization,the rationality of the optimization result is illustrated.In order to obtain higher torque density,the paper further optimizes the motor weight.Under the premise of ensuring the torque performance unchanged,the stator yoke is slotted and the inner diameter of the rotor is directly increased.The result shows that the weight reduction is obvious.Due to the worst bearing condition of the rotor,the influence of the magnetic bridge length and the inner diameter of the rotor on the mechanical strength is studied.The stress distribution of the rotor under the combined action of the electromagnetic force and the centrifugal force is verified by one-way sequential coupling method.Finally,the loss of the motor is analyzed and the distribution of iron loss and permanent magnet eddy current loss is obtained.Then the paper calculates the efficiency and the results show that the design requirements can be met.