The Research On Common-Mode Voltage About The System Of Driving Asynchronous Motor By PWM-Inverter

As the high-frequency power electronic switches are widely used in railway traction systems,and enhancing the performance of the motor control system but also having a negative impact to the traction system.Due to the asymmetric and instantaneous output of the PWM inverter in the railway traction systems,there will produce common-mode voltage in the the traction system,then resulting in the shaft voltage,current and other negative effects on the asynchronous motor system,which affect seriously the safety and reliability of the traction system.Therefore,researching the formation mechanism,the impact of process and the suppression strategies of the common mode voltage,that is important to enhance the safety and reliability of railway traction system.Firstly,this paper will analyze the PWM inverter’s working principle and common-mode voltage,and understanding the related characteristics of the common-mode voltage.Secondly, on the basis of understanding the basic working principle and structure of the asynchronous motor,there is to analyze the mode-model and the impact of common-mode voltage for the asynchronous motor,especially the shaft voltage’s principle and the shaft current’s flow path.Then,on the based of analysis of the PWM inverter and the asynchronous motor,it is proposed the suppression strategies of common-mode voltage,including hardware and software strategies,and to analyze the suppression principles.Finally,using Matlab/Simulink simulation software is to build the simulation model according the theory asynchronous motors PWM inverter drive systems analysis.The simulation includes the following aspects,how to affect the common-mode voltage,the shaft voltage,the dv/dt current and the EDM current by changing SPWM modulation parameters,researching the impact of the DC-powered models and the filter for common-mode voltage,and how to affect the common mode voltage,the shaft voltage and the shaft current by using the SVPWM,the NZPWM and the DTC.Through researching theoretical and analyzing simulation,hardware suppression strategy of common-mode voltage has some advantages,but does not fundamentally eliminate the common-mode voltage,that not only increases the complexity of the system,but also higher cost of hardware and lower versatility,so it is uneconomical.And according to analyze the control strategy to suppress common mode voltage,software suppression strategy don’t need to increasing extra hardware device,but also the versatility of the software suppression is better,and it can basically meet requirements for suppressing common-mode voltage in the traction system. If combinating the advantages of suppression measures between the hardware and the software, which can be the lowest cost to achieve the best results.