Design Of Permanent Magnet Motor For Electric Bus

With the development of science and technology,environmental pollution problems become more and more serious,the frequent occurrence of haze weather affects people’s physical and mental health of people seriously.Popularizing electric vehicle energetically is one method to solve environmental pollution problem,electric vehicle consumes electric energy and does not emit exhaust gas,which can reduce dust particle in the air.In the electric vehicle motor system,motor is a very important part.The common motor works at a rated point.Relatively speaking,the working scope of electric vehicle is wide,so the design is different form common motor.The motor of electric vehicle should have the characteristics of high flux-weakening capability,high power density and wide range of high efficiency,therefore,the design of electric vehicle motor must focus on these three considerations.Based on the characteristics of the electric motor,the electromagnetic design,the flux weakening performance and the torque fluctuation of the motor are studied.The main contents are as follows:Firstly,the magnetic structure of the rotor is studied.The magnetic structure of the rotor have important significance on the property of motor.Five kinds of magnetic structures of rotor were selected so as to compare the property of different rotor structures through finite element software simulation,such as cogging torque,torque ripple,gap flux density,torque-current curve,etc.Torque-speed curve of motor with different magnetic structures are simulated using finite element software.Moreover,proper magnetic structure of rotor is selected after comparing the property of motor with different magnetic structures and combining with the characteristics of the motor to be designed.Secondly,electromagnetic design of motor is made.Through comparing motor with different number of poles,the paper analyzed the impact of motor efficiency map and flux-weakening speed extension capacity and the torque property so as to determine suitable number of poles for motor.Through analyzing the distribution of high-efficiency zone of motor,the paper determined the turning speed of motor.The influence of permanent magnet size on the flux weakening and torque capacity of the motor is analyzed.Through analyzing the magnetic induction intensity of yoke in different working conditions,the width of yoke is changed so as to reduce the loss of motor.Finally,the torque ripple of motor is studied.Torque ripple affected the performance of motor,increases the noise of motor and affects the comfort degree of passenger.Three methods are adopted to reduce the torque ripple,such as non-uniform air gap,the rotor step skewing and optimized arc coefficient of permanent magnet.