Study On Design And Output Characteristics Of Permanent Magnet Synchronous Motor For Electric Vehicle

With the proposal of the national energy strategy,electric vehicles have been widely used.In order to adapt to the complex and changing driving conditions of electric vehicles,the drive motors for electric vehicles need to have high torque output capabilities,a wide speed range and high efficiency.This topic comes from the Liaoning Province Excellent Talent Project "Research on the Weak Magnetic Characteristics and Output Capability of Permanent Magnet Synchronous Motors for Electric Vehicles".The project number is LJQ2015082.The driving motors of electric vehicles are mainly based on permanent magnet synchronous motors.For this purpose,a permanent magnet synchronous motor with a rated power of 30 kW and a rated speed of 3000 rpm is designed for this vehicle,and researches on the electromagnetic design of the motor,cogging torque optimization,output characteristics analysis,iron loss calculation and analysis,efficiency optimization,etc.The work of this article mainly includes the following parts.The first part focuses on the control method of the maximum torque / current of the electric vehicle motor,and studies the electromagnetic calculation method and process of the motor.When the motor is running in the constant torque zone,the iron loss of the motor is small,and the copper consumption of the motor accounts for a large proportion.In order to reduce the copper consumption of the motor,this paper has studied the electromagnetic design method of the motor to control the stator current with the principle about the ratio of maximum torque to current.according to the rated power 30 kW,rated speed 3000 rpm and other performance indicators to determine the main structural parameters of the motor slot,winding,permanent magnet and so on.Among them,the cogging torque specific to permanent magnet motors will affect the low-speed performance and positioning accuracy of the motor in the control system.Therefore,in order to suppress the cogging torque of the motor and optimize the motor performance,in this paper,the finite element simulation of the motor is combined with the cogging torque analytical formula to study the influence law of the pole arc coefficient,the pole slot matching,and the eccentric rotor structure on the cogging torque.In the second part,in view of the complex and ever-changing driving conditions of automobiles,the different driving conditions have different performance requirements forvehicle permanent magnet synchronous motors,and the effect of the turning speed on the output characteristics of the motor is studied.For an electric vehicle that is running frequently under frequent start-stop and acceleration / deceleration conditions,the motor is required to have superior low-speed output performance.When the electric vehicle is operated at high speed for a long time,the motor is required to have superior weak magnetic expansion performance.Because the turning speed of the motor between the constant power area and the constant torque area has an important influence on the maximum torque and maximum power output by the motor,and the relationship between the rated motor speed and the turning speed has a very important influence on the motor performance.To this end,this paper studies the influence of the turning speed on the maximum power and maximum output torque of the motor,and determines the turning speed of the motor according to the different working conditions and performance requirements of the motor,and defines the relationship between the rated speed and the turning speed of the motor to guide the design of motor structural parameters.The third part focuses on the characteristics of the motor working in the field weakening region,and studies the calculation of the iron loss of the motor and the analysis of the change law and the method of improving the proportion of the motor's high efficiency area.The iron loss of the motor depends on the distribution of the magnetic density of the motor.In the field weakening region,the motor magnetic field changes with the change of the field weakening current,so that the iron loss of each working point of the motor is different.Therefore,in order to calculate the performance of the motor more accurately,this paper obtains the iron loss of the motor through the segmented variable coefficient iron loss calculation method,and further analyzes the influence law of the field weakening depth on the iron loss of the motor.For ordinary permanent magnet synchronous motors,the performance calculation of the motor has a relatively mature formula method,which is relatively simple to design.The performance of the motor only requires the calculation of the rated point,and the speed regulation performance is not high.For the permanent magnet synchronous motor for vehicles,the performance of a certain point can no longer be calculated in the design of the motor,and the performance calculation must be performed at each speed point to obtain the efficiency map of the motor.By analyzing the efficiency distribution of the motor in the entire speed regulation area,and further studies measures to increase the proportion of the motor's high efficiencyarea.