Research On Control Strategy Of Permanent Magnet Synchronous Motor Traction System For Rail Transit

Permanent magnet synchronous motor has the advantages of small volume,high efficiency and high power density.Especially the interior permanent magnet synchronous motor(IPMSM)has wide flux weakening speed range by using reluctance torque.Because of these characteristics,the permanent magnet synchronous motor traction system has gradually replaced the existing asynchronous motor traction system and become the future development trend of rail transit.However,due to the complex operation condition of traction motor as well as the high power and low switching frequency of traction converter,the common motor control strategy and modulation strategy are difficult to meet the special requirements of rail transit traction system.This paper takes permanent magnet synchronous motor traction system as the research object,and analyses IPMSM vector control strategy and multi-mode hybrid PWM strategy for rail transit respectively.The two strategies complement each other to complete the control of the whole traction system.This paper is mainly divided into three parts:Firstly,according to the requirement of high output torque and wide speed range of the traction motor,based on IPMSM mathematical model and vector control theory.This paper combines the maximum torque per ampere(MTPA)control and phase-shift flux weakening control,and analyses an IPMSM vector control strategy for rail transit,that provides a motor control strategy for follow-up research.Secondly,according to the special requirements of traction converters for low switching frequency and high voltage utilization,the traditional multi-mode SVPWM modulation strategy is introduced in detail,and the shortage of high low-order current harmonic content when the carrier ratio is low has been analyzed.This paper,using the selective harmonic elimination pulse width modulation(SHEPWM)in the high frequency region to improve the shortcomings of the traditional multi-mode SVPWM modulation strategy,designs a multimode hybrid PWM strategy combining SVPWM and SHEPWM.And the problem of carrier ratio switching and SHEPWM implementation in each frequency band have been solved.Finally,through system simulation,the superiority of the IPMSM vector control strategy for rail transit in improving motor torque output capability and flux weakening speed-expansion capability and the effectiveness of the multi-mode hybrid PWM strategy for reducing torque ripple and maximize DC voltage utilization have been verified.And then through designing the corresponding software algorithm on the experimental platform,and testing the dynamic performance of the system,the practicability of the vector control algorithm has been verified.