Stability Analysis Of Low Frequency Oscillation Of Vehicle-grid System Considering Phase-locked Loop In Rectifier Of EMUs

In high-speed railway,under the condition of multiple EMU’s preparation,the lowfrequency oscillation of vehicle-grid system’s voltage may occur,which will affect the normal running of trains,and seriously affect the safe running of high-speed railway.The phase-locked loop(PLL)of the rectifier will affect the electrical stability of vehicle-grid system.However,the current research on the suppression of low-frequency oscillation is mostly analyzed from the aspects of the variation of vehicle side parameters and different control modes,etc.,while the study on the improvement of PLL in EMU rectifier is relatively lacking.Therefore,it is of great theoretical and engineering significance to study how to improve the phase-locked loop in the EMU rectifier so as to suppress the low frequency oscillation of vehicle-grid system.Aiming at the problem of low frequency oscillation suppression of vehicle-grid system by phase-locked loop,this paper analyzes the influence of various parameters of phase-locked loop in CRH5 EMU rectifier on the stability of low frequency oscillation of vehicle-grid system.By improving the structure of phase-locked loop,the low frequency oscillation suppression of vehicle-grid system can be realized and the electrical stability of vehicle-grid system can be improved.Firstly,the influence of the parameters of the PLL on the stability of the low frequency oscillation of the vehicle-grid system is analyzed.The SOGI structure and dq structure were improved and the dynamic response analysis before and after the improvement was carried out.An improved PLL model is obtained.Secondly,the dq small signal model of the improved PLL is derived in detail.The influence formula of the phase error of the improved PLL on some signals in the control is calculated.An improved PLL based rectifier dq impedance model was established.The validity and accuracy of the model were verified by impedance measurement method.The MATLAB simulation model based on the improved phase-locked loop is established.A hardware-in-the-loop experimental model based on the improved phase-locked loop is established.Finally,under the condition of low frequency oscillation of vehicle-grid system caused by different parameters,the stability of vehicle network system before and after the improved PLL was analyzed and verified by the influence of the improved PLL on the Zdd low frequency negative impedance,combined with the generalized Nyquist stability criterion,Matlab simulation and the HIL experiment platform based on Starsim.The above analysis and verification show that the improved PLL can effectively suppress the low frequency oscillation and improve the stability of the vehicle-grid system.The mechanism of the improved PLL to suppress the low frequency oscillation of the vehicle-grid system is revealed,which provides a design reference for the research on how to suppress the low frequency oscillation of the vehicle-grid system.