Research On Harmonic Resonance And Its Suppression Technology Of AT Traction Network

With the extensive uses of AC-DC-AC locomotive in high-speed railway,the 3,5,7 inferior low-band harmonics have decreased significantly in traction power supply system,but at higher frequencies(such as more than 20 times)the higher harmonic content have increased.Resonance phenomenon of train and traction network excited by higher harmonic causes the tripping of the substation,the burning of the arrester and the train outage and so on.In this paper,the impedance frequency characteristic of AT traction power supply system,its influencing factors and transmission characteristics of high harmonic current in traction power supply system are analyzed.The mechanism of harmonic resonance of AT traction power supply system and electric locomotive is studied and the reasonable and feasible scheme to restrain harmonic resonance is put forward.In this paper,the impedance frequency characteristic of the traction power supply system is summarized,the AT traction power supply system widely used in our country is taken as the research object,the classical Carson theory and electromagnetic field theory are used to establish the multi-conductor equivalent ? model of traction power network.A simulation model is built in MATLAB/SIMULINK.Based on the spectrum analysis method and harmonic amplification method,the impedance-frequency characteristics and harmonic current amplification under five conditions are analyzed in this paper,which include different locomotive positions,different lengths of traction lines,different short-circuit capacity of external power supply,different AT leakage reactance and three modes of AT Power supply system.The regularity of harmonic resonance of AT Power supply system is revealed.The generation mechanism and characteristics of parallel resonance and series resonance are analyzed.The simulation results verify the conclusion that the harmonic current may cause the over voltage,over current and harmonic distortion in the traction network.The application of passive filtering technique to suppress resonance over-voltage is proposed.Combined with the current strategy of setting passive filter on the traction network to suppress harmonic resonance,the impedance frequency characteristics and power consumption of several high pass filters are analyzed.Considering the filter structure and filtering effect,the second-order high-pass filter is selected as the harmonic suppression scheme.The installation position,switching transient process and protection mode of the second-order high pass filter are analyzed.The simulation results show that the second-order high pass filter can effectively filter out the harmonics under four conditions which include different modes of AT Power supply system,different short-circuit capacity of external power supply,over zone feeding situation and AT transformer in disconnecting situation.