Research On Hybrid(Ce,Nd)-Fe-B Synchronous Motor For Electric Vehicle

Because of the low magnetic properties and the weak anti-demagnetization ability of ferrite permanent magnets,the overload ability of hybrid permanent magnet synchronous motor with ferrite and Nd-Fe-B for driving electric vehicles is weak and the risk of demagnetization is high.Thus,in this paper,(Ce,Nd)-Fe-B and Nd-Fe-B hybrid permanent magnet synchronous motor are studied.(Ce,Nd)-Fe-B have better magnetic properties than ferrite permanent magnets and lower price compared with Nd-Fe-B permanent magnets.However,at present,(Ce,Nd)-Fe-B have poor heat resistance.Therefore,how to reasonably design the electromagnetic and cooling structure according to the characteristics of(Ce,Nd)-Fe-B permanent magnet materials is an important subject in the research of(Ce,Nd)-Fe-B and Nd-Fe-B hybrid permanent magnet synchronous motor.Chapter 1 summarizes the literature related to hybrid(Ce,Nd)-Fe-B synchronous motor is studied,including the research status of(Ce,Nd)-Fe-B and hybrid permanent magnet motor,the research status of motor loss,temperature rise and motor cooling system.In Chapter 2,different pole slot matching,stator split ratio and rotor structure of hybrid(Ce,Nd)-Fe-B synchronous motor for 50 kW electric vehicle are studied.Then compared with Nd-Fe-B motor,the torque performance and the cost of permanent magnet are mainly analyzed,and the performance-price ratio of the two is evaluated.In Chapter 3,the loss of hybrid(Ce,Nd)-Fe-B synchronous motor with optimal structure is studied,mainly for electromagnetic loss and mechanical loss.Combining with the existing analytical calculation method of iron loss,the iron loss curve equation is re-fitted.The iron loss of the motor is calculated by the re-fitted iron loss equation and compared with the simulation.The copper loss is decomposed into DC loss and AC loss.The different models are compared,the total copper loss at different frequencies and the eddy current loss of the permanent magnet at different current sources are compared.The mechanical loss mainly includes the wind friction loss of the rotor and the friction loss of the bearing.The wind friction loss of the rotor is analyzed and compared with the finite element simulation.The common calculation formula of the bearing friction loss is given,and the relationship between the friction loss and the speed of the motor isanalyzed.The heat density of the heat source inside the motor is obtained by loss analysis,and the flow field of the heat transfer inside and outside the motor is analyzed.The convective heat transfer coefficients of the walls of the motor at different rotational speeds are obtained.Based on the above work,the steady-state temperature rise and transient NEDC temperature rise of external water-cooled motor are analyzed.Then the influence of temperature rise on the safety of motor structure,electromagnetic performance and anti-demagnetization ability is analyzed.In Chapter 4,the cooling system of the motor is studied,and the effects of different cooling water structures,different number of cooling water channels,different inlet velocity of cooling water and different cross-sectional shape of cooling water on the cooling effect of the motor are analyzed and simulated.Then the internal oil cooling of the motor is simulated and analyzed,and the optimal cooling system of the motor is obtained.The steady-state temperature field is analyzed,and the steady-state temperature rise of the motor before and after optimization is compared.In Chapter 5,a 3.7kW hybrid(Ce,Nd)-Fe-B synchronous motor prototype was trial-manufactured.The experiments of no-load back-EMF,no-load mechanical loss,no-load iron loss and load temperature rise are carried out and compared with the simulation results.Chapter 6 summarizes and prospects the whole paper.