| Recently,in traction power supply systems(TPSSs),high-order harmonic resonance accidents occur frequently,because of the adoption of high-power,high-speed,high-density AC drive electric locomotives.These resonant accidents would destroy ground or on-board equipment.In some severe cases,these accidents would result in traffic interruptions which seriously threaten the safety of TPSSs.Therefore,it is necessary to study the mechanism of high-order harmonic resonance,so that people can find out the solution to suppress locomotive-network resonance and solve locomotive-network electrical coupling problems.The traction transformer of rolling stocks plays an important role in the high-order harmonic resonance,and this thesis focuses on the study of the harmonic modeling method for traction transformer and analyzing the influence of traction transformer on the mechanism of high-order harmonic resonance.Firstly,the characteristics of traction transformer are studied in this thesis,including its specified operating conditions,particular design requirements and special load.Two types of practical traction transformer are analyzed in order to illustrate the internal structure,like winding and iron core.The power frequency model of single phase multi-winding transformer have also been studied,and all existing models are described and summarized.Secondly,the impact of harmonics on transformer have been researched.This thesis takes various factors,like skin effect,nonlinearity of core and distributed capacitances into consideration,and proposes a winding modeling method based on vector fitting and circuit synthesis.Besides,a new method to establish the nonlinear characteristics of the iron core is proposed.Then,the power frequency modeling method for single phase multi-winding transformer has been combined with the harmonic modeling method,so a unified harmonic modeling method for traction transformer is proposed.Thirdly,with the cooperation of CRRC Zhuzhou Electric Co.,ltd,the harmonic test for TBQ79-2800/25 type traction transformer is accomplished,the testing results have been well analyzed.Based on the testing data,the harmonic modeling procedure is described thoroughly,and a harmonic model for this transformer which can describe the harmonic characteristics from 0 to 5000 Hz has been established.The feasibility and accuracy of this proposed model have been verified.Finally,the effect of traction transformer on high-order harmonic resonance has been evaluated.The harmonic model of traction transformer is used in the locomotive-network simulation to study its influence on the transmission of harmonic current.Besides,the influence of asymmetry for winding has also been studied,and the analytical expressions of harmonic current are derived.This paper also study the impedance-frequency characteristics of TPSSs under different operation cases,and research results show that the number of locomotives can change the resonant frequency of the TPSS.This research results not only contribute to study the harmonic model of traction transformer for rolling stocks,but also support the study on the mechanism of high-order harmonic resonance in TPSSs. |
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