Research On Magnetical Characteristics And Thermal Characteristics Of Spoke-type Flux- Concentrating Permanent Magnet Synchronous In-wheel Motor

Due to the high efficiency and good mobility,the distributed drive type has become a new direction in the field of electric vehicle.This kind of electric vehicle takes the in-wheel motor(IWM)as the power component,as well as saving the traditional mechanical connections and improving the acceleration performance.Thus,it has become a hot spot in the field of motor.As the motor is placed inside the wheel,the space is strictly limited so that its electromagnetic performance and lubrication cooling are severely affected.In order to solve these problems,this doctoral dissertation studies the electromagnetic structure design,magnetic field analysis and calculation,loss analysis,heat dissipation optimization and accurate modeling in temperature field.The main research work includes the following aspects:A type of spoke-type flux-concentrating permanent magnet synchronous inwheel motor(STFC-PMSIWM)is proposed.The improved subdomain method is used to establish the air-gap field analytical model to solve the problem,where the traditional methods cannot deal with the special structure and core saturation,so as to effectively improve the calculation accuracy of the analytical method.On this basis,the analytical expressions of key parameters such as air-gap flux density,winding flux linkage,back EMF and electromagnetic torque are obtained through theoretical derivation.Compared the analytical results with the finite element method results and experiment results,it is verified that the magnetic field analytical model is accurate,providing a theoretical reference for the analysis of this type of machine.The narrow space and airtight working condition are poor factors for cooling,especially for in-wheel motors.The losses are the main factors resulting in the temperature rise.Therefore,this section of the doctoral dissertation studies the calculation and suppressing methods of additional copper loss,iron loss and permanent magnet eddy current loss.Aiming at solving the problem of additional copper loss caused by the tangential flux-concentrating structure,the analytical method is used to calculate the copper loss.According to the effect of current,frequency,conductor diameter and winding arrangement on the additional copper loss,this paper proposes the certain methods to suppress the loss.Based on the magnetic field analytical model,the calculation equations of the iron loss are deduced in this doctoral dissertation.On this basis,the factors working on iron loss are analyzed,and the iron loss distribution regularities are revealed.A new analytical method of rotor structure optimization is proposed to suppress of iron loss.The current harmonics and permanent magnet blocking severely impact the loss.This doctoral dissertation conduct a detailed analysis on each working factor.According to the characteristics of each factor,the approach to restrain the permanent magnet eddy current loss is studiedAiming at alleviating the problem of heat dissipation caused by the limited space and airtightness of the in-wheel motor,the water jacket structure and design method of the cooling system are the key factors.According to the structural characteristics of the water cooling for in-wheel motor and the heat transfer mode,the temperature field model is established and the key factors that restrict the cooling performance are analyzed.Combined with theoretical derivation and analytical calculation,the influences of the cooling water channel size,the contact gap between the stator and frame,the properties of slot insulation material and the slot size parameters on the cooling mechanism are investigated to explore how to suppress each negative factor.This will provide a valuable reference to design and optimize the similar type of machine.In order to accurately calculate the temperature rise,a refinement modeling method in the temperature field is proposed.The accuracy of temperature rise is verified by comparing the models with different specifications.Meanwhile,the selection principle of the model specifications is determined.The expansion volume method is used to embody the effect of gap between the stator and frame,and the effect of the contact gap on the temperature rise is also studied.Due to the existing problems of traditional winding equivalent model,the improved multi-layer equivalent modeling method is proposed and a theoretical system of the multi-layer model is established.Combining with the distribution of iron loss,the effect of different heat source loading methods on temperature rise is analyzed,which can efficiently determine the most effective loading method.By the comparison between simulation and experiment results,the accuracy of the temperature field model is verified.