Study On Loss Mechanism And Efficiency Improvement Of Brushless DC Motors For Electric Vehicles

The emergence of electric vehicles has solved the problem of pollution caused by the exhaust of fuel vehicles and alleviated the energy shortage.This article takes the brushless DC motor(BLDC),which is the core part of the electric vehicle,as the research object.It mainly studies the loss mechanism and the method of improving the efficiency.The main content of this paper is as follows:(1)Analyze the operating principle of brushless DC motor and establish a mathematical model of brushless motor based on this.Then set up a BLDC simulation model in Matlab/Simulink.The control effects under the two different control methods of speed single-closed loop,speed and current double-closed loop are compared,and the factors that affect the speed control performance of the motor are analyzed.(2)Analysis of the losses generated by various parts of the motor.By establishing the BLDC Bertotti iron loss discrete model and programming in Matlab,the curves of iron loss with flux at different frequencies are obtained.It is known that under normal operating conditions,we need to reduce the motor speed as much as possible which can reduce the motor loss to a great extent.Through the use of finite element simulation software,we simulate the change in the number of motor poles and stator yoke height.The change of the brushless DC motor loss with the yoke height and the number of poles can be seen from the analysis results that the total motor loss decreases as the stator slot area decreases and the motor pole count decreases first and then increases.This causes the total loss of the motor to have a minimum loss point in the selection of the number of poles and slots.Therefore,when designing the motor,finding the minimum loss point can achieve the purpose of optimizing the motor design,that is,increase the motor efficiency.(3)The experiment of brushless DC motor efficiency measurement was carried out using the upper computer LabVIEW.The torque corresponding to the highest efficiency was found through the corresponding torque data processing of different parameters,and the highest efficiency point was found.Established experimental basis for motor efficiency improvement(4)The analysis of the motor cooling system was carried out and a simple mathematical model of the cooling system was established.Through the reduction of the motor operating temperature,the purpose of reducing the loss of the motor and increasing the efficiency was achieved.(5)Design and analysis of the software and hardware of the brushless DC motor,and design the hardware circuit based on STM32F103C8T6 microprocessor as the main controller,mainly including the power supply circuit,drive circuit,detection circuit,inverter circuit and other modules;software design includes The design of the main program,the design of the interrupt subroutine and the commutation design of the Hall sensor,the design of software and hardware establish the basis for the efficiency measurement test...