Study On Voltage Oscillation Of High-speed Railway Traction Network And Train Coupling System

With the rapid development of China’s high-speed railway,the problems of high-frequency resonance and low-frequency oscillation caused by improper electrical matching between high-speed train and traction power supply system have become increasingly prominent due to the lack of thorough and comprehensive understanding of the characteristics of traction power supply system and high-speed trains,which brings potential safety hazard to the high-speed railway system equipment and train operation and seriously affects the power supply quality of the traction power supply system and on-time operation of the train.In the thesis,the network voltage oscillation of high-speed railway traction network and train coupling system is taken as the research object,two phenomena of high frequency resonance voltage and low frequency fluctuation of traction network are studied,and the generation mechanism,influential factors and restraining measures of these two phenomena are analyzed emphatically,which provides theoretical support for the actual control of network voltage oscillations of high-speed railway traction network and train coupling system.This thesis firstly introduces the components of the traction power supply system with AT power supply and the composition and control method of the CRH3 EMU.Based on the Matlab/Simulink simulation software,the simulation model of high-speed railway traction network and train coupling system is established,which provide a simulation platform for the simulation analysis of high frequency resonance and low frequency oscillation.Based on the simulation platform,the simulation reproduces the phenomenon of high frequency resonance and network voltage fluctuations.In order to find out the signal components contained in the network voltage during high-frequency resonance and low-frequency oscillation,Prony algorithm and FFT algorithm are used to detect and analyze the network voltage signal of the traction network with high frequency resonance and low frequency oscillation.It is found that the traction network voltage signal contains high harmonic component when the high-frequency resonance and contains inter-harmonic component when the low-frequency fluctuations,and the voltage fluctuation frequency of low frequency oscillation is the difference between the interharmonic and the adjacent harmonic or fundamental.Aiming at the problem of high-frequency resonance,the harmonic characteristics of AC trains and the drag-frequency characteristics of traction network are theoretically calculated and analyzed.The distribution rules of harmonic voltage on the AC side of the train converter and impedance characteristics of traction network are clarified.Through the theoretical calculation and simulation analysis,it is found that the harmonic content of the traction network voltage is larger when the frequency of AC voltage harmonics of the train converter coincides with the frequency of the traction network resonance point,and the harmonic content of traction network increases with the traction network impedance It will lead to the emergence of traction network resonant overvoltage when the traction network voltage harmonic content is very large.Aiming at the problem of low-frequency oscillation,the analysis of the waveform shows that the train converter has not achieved the two control objectives of unit network power factor and stable DC voltage during low frequency oscillation,and the system stability has been destroyed.The factors that affect the stability of the traction network and train coupling system and the stability of the train converter control system are analyzed theoretically.The simulation shows that the traction network voltage is more prone to low-frequency oscillation when the number of trains running under the same power supply arm is greater,the distance between the train and the substation is farther or train inverter current inner loop control parameters KiP value is smaller,voltage outer loop control parameter KvP value is larger or parameter KvI value is smaller.Finally,for high-frequency resonance problem,this thesis introduces three kinds of suppression methods:changing the carrier frequency of train converter,changing the length of power supply arm and adding damping filter.For low-frequency oscillation problem,a train converter control method based on sliding mode variable structure control is designed to replace the traditional PI control.Through simulation,the inhibition effect is good.