Research On Design And Cross-coupling Of Permanent Magnet Assisted Synchronous Traction Motor

Under the theme of energy conservation and emission reduction,the advantages of high efficiency and low loss of permanent magnet traction system make it gradually become the development direction of the next generation of rail transit.However,the problems of high back EMF during coasting with high speed and difficulty in re-running at a speed hinder the popularization and application of permanent magnet traction system.Permanent magnet assisted synchronous reluctance motor has the characteristics of both permanent magnet synchronous motor and synchronous reluctance motor and can make full use of the reluctance torque of the motor.It has many advantages such as small amount of permanent magnets and low back EMF,which is the best choice to solve the above problems.However,the large torque ripple and the sensitivity of the motor performance to changes in inductance parameters limit its further application in the traction system.This paper aims at suppressing motor torque ripple,exploring the influence of inductance parameter changes and cross-coupling inductance on motor control algorithms.Firstly,comparing the permanent magnet synchronous motor and the synchronous reluctance motor,the structural characteristics and performance advantages of the permanent magnet assisted synchronous reluctance motor are explained.According to the actual requirements of the traction system,a permanent magnet assisted synchronous traction motor with high power and low back EMF was designed,which effectively solved the problem of high back EMF during coasting with high speed and difficulty in re-running at a speed when the permanent magnet motor is used in the traction system.Aiming at the shortcomings of the large torque ripple of the motor,a new type of rotor structure and design method with a non-uniform air gap and unequal width magnetic bridge is proposed,which effectively suppresses the torque ripple of the motor and improve the smoothness of the motor operation.The finite element analysis software was used to simulate the motor design scheme and the new rotor structure design method,which proved the effectiveness of the scheme and method.Secondly,the change characteristics of the q-axis inductance,d-axis inductance and cross-coupled inductance of the high-power permanent magnet assisted synchronous reluctance motor under different loads are analyzed.Aiming at the problem that motor performance is easily affected by changes in inductance parameters,a variable parameter MTPA control algorithm based on equivalent inductance is proposed,compared with the constant inductance parameter MTPA control algorithm,the proposed variable parameter MTPA control algorithm considering the inductance parameter change and the cross-coupled inductance has a better current control strategy under the same torque,and effectively reduces the motor loss,Simulink simulation and experiment verify the effectiveness of the control algorithm.Aiming at the problem that the EKF flux identification method based on constant inductance parameters is inaccurate and the error is large when the motor is running under high torque and magnetic saturation conditions,a variable parameter EKF flux identification algorithm is proposed,which fully considers the influence of inductance parameter changes and cross-coupled inductance,effectively eliminates the flux identification error,and greatly improves the accuracy of the flux identification.Simulation experiments verify the effectiveness of the algorithm.Finally,a 250 k W permanent magnet assisted synchronous traction motor was trial-produced according to the design scheme proposed in this paper,and no-load loss experiment and load characteristic experiment were carried out on the motor respectively.The experimental results show that the designed motor can meet the actual operation requirements,verifying the feasibility of the design scheme and the effectiveness of the control algorithm.