Analysis And Suppression Of Low Frequency Oscillation In Traction Power Supply System

With the rapid development of China’s high-speed railway,the operating mileage of high-speed railway has reached 38,000 km by 2020,covering more than 95% of cities with a population of one million or more.With the rapid development of high-speed railway,the low-frequency oscillation of high-speed railway traction power supply network and EMU coupling system is becoming more and more frequent,which seriously affects the safety and stability of high-speed railway operation.Taking CRH3 EMU as the research object,this thesis builds a simulation model of vehicle network coupling system,and focuses on the mechanism,influencing factors and suppression strategies of low-frequency oscillation phenomenon.Firstly,the components of traction power supply system are introduced,the calculation method of conductor parameters of traction network is given,and the topology of CRH3 EMU traction drive system and the control strategy of four quadrant converter are described.Based on MATLAB /Simulink software,the time-domain simulation model of train network coupling system of high-speed railway is established,the phenomenon of train network low-frequency oscillation is reproduced,the correctness of the simulation model is verified,and a simulation platform is provided for the research of train network low-frequency oscillation.Secondly,the equivalent impedance of traction power supply system and EMU is calculated respectively.The stability of vehicle network coupling system is analyzed by using the stability analysis method of impedance ratio,and the generation mechanism of low-frequency oscillation is explained.According to the impedance ratio criterion and Bode diagram theory,the effects of traction network power supply line length,traction transformer capacity and EMU control parameters on the stability of vehicle network system are explored,which provides a theoretical basis for the suppression strategy of vehicle network low-frequency oscillation.Finally,combined with the stability analysis of vehicle network coupling system,the effectiveness of restraining low-frequency oscillation by regulating the number of simultaneous starts of EMUs and the control parameters of converter voltage loop is verified.A low frequency oscillation suppression strategy based on improved STATCOM is proposed.The strategy adopts STATCOM device based on fuzzy control to compensate the dynamic reactive power of traction network side voltage,so as to suppress low-frequency oscillation.The simulation results show that compared with the traditional PI control STATCOM suppression strategy,this strategy can more effectively suppress the phenomenon of low-frequency oscillation and ensure the stable operation of EMU.