Application Of Modal Analysis Method In Harmonic Analysis And Elimination Of Electrified Railway

Harmonic is always an urgent problem to be solved in electrified railway.With the AC-DC-AC electric locomotive running situation is becoming more and more popular,the harm caused by the harmonic current injected into the traction network has been paid more and more attention by the operation and research departments.Different from the AC-DC locomotive,the AC-DC locomotive has the characteristics of wide frequency range and low harmonic content.Once the input harmonic excited the traction network system to the occurrence of resonance,it will endanger the power supply safety of traction network system,and even affect the stable operation of the public power grid.The resonance characteristics of railway lines was analyzed by using the modal analysis method,basing on the study of harmonic resonance mechanism.In order to have a good preparation for the next step of work,firstly discussed the equivalent model of the traction network,then by considering the chain structure of the whole network traction,this article analyzed several abstract modeling of common connection modes of traction transformer and built up mathematical models of transverse connection element as well as longitudinal connection element.Finally,the circuit system model was simplified by basing on the theory of Carson.Secondly,in the process of establish the railway system model,admittance matrix differences caused by the selection of different node unit length and the ignorance of the traction network line parameters' distribution characteristics are likely to impact the analysis results,and these two points are often overlooked in modal analysis.To solve these problems,an equivalent traction network model was built in Matlab/simulink software platform,considering the distributed parameter circuit characteristics.Determine the harmonic resonance frequency,influence scope and the results excursion in different ways of segmentation in this modal by modal analysis method.Finally,find the laws of modal analysis in different ways of segmentation,and draw a conclusion on when considering the line parameters' distribution characteristics can improve the accuracy of modal analysis results.Thirdly,the modal analysis method was used to analyze the harmonic characteristics of the AT traction network.Taking single AT traction network as the research object,this paper analyzed the change of the resonance frequency as well as the influence of resonance center when the locomotive is moving from one AT to the next AT.In addition,study the AT traction network under the mode of over zone feeding by means of modal analysis,when the traction network failure or need power outage maintenance.Then reach a conclusion on the differences between its resonance characteristics comparing with the normal power supply.At last,the influence of locomotive running position on the resonance point is discussed.Finally,the permeability characteristics of the harmonic current from the traction network to the public power grid were analyzed.Several factors that influence the seepage condition are obtained,which provided guidance for the harmonic elimination.The change of the modal characteristics after the wave-trap high-pass filter join the system was analyzed,Then discussed the selection of the parameters of wave-trap high-pass filter from three aspects,the impact value of capacitance,inductance and resistance,and finally puts forward some reasonable filter parameters.