Research And Performance Analysis Of Flux-weakening Control Of Permanent Magnet Synchronous Motor In Electric Vehicles

In the electric vehicle industry,permanent magnet synchronous motors(PMSM)with high torque,high power density,and high efficiency are widely used.In order to meet the requirements of the speed increase at rated speed about the permanent magnet synchronous motor as the controlled object,we need to control the motor with fluxweakening control,reduce the back EMF of the motor by weakening the magnetic field of the motor's permanent magnet.This paper studies the flux-weakening control method and designs an adaptive flux-weakening control method and validates it experimentally.The main work includes:1.This paper studies the structural classification of permanent magnet synchronous motors as controlled objects,and analyzes the mathematical model under different coordinate systems,then analyzes the transformation method between mathematical models.This paper studies in detail the vector control method of permanent magnet synchronous motor control and its various control strategies and space vector modulation techniques applied in electric vehicles.2.Based on the motor mathematical model and vector control,this paper analyzes the principle of flux-weakening control in detail.This paper studies and analyzes the formula method,table look-up method and PI feedback method commonly used in current engineering projects,and summarizes the defects that still exist in practical applications.3.In order to avoid the problems in the application of traditional flux-weakening control methods,based on the traditional flux-weakening control method,this paper proposes an adaptive flux-weakening control method based on motor voltage modulation ratio(Delta method).This method judges the motor voltage modulation ratio and changes the motor excitation current by superimposing small current values to achieve the purpose of controlling the motor voltage.And in the motor constant torque operating area with the maximum torque per ampere(MTPA)control,in order to achieve the optimal torque control effect.Experimented and analyzed the results of the proposed method,a comparative experiment with zero-axis current control is performed on a motor experimental platform.The results show that this method has achieved the effect of flux-weakening control and test the feasibility of the method.Next,a full-speed motor operation experiment was conducted on an experimental platform equipped with different motors,test the effect of this method in the full speed range.Finally,an actual engineering application test is performed on the electric vehicle-mounted motor,the electric vehicle can stably achieve the effect of speed increase and perform full-speed range operation under the effect of this method,test the practicality of the method.