Application Of Inductive Filtering Technology In Metro Power Supply System

Metro power supply systems are elements of hybrid AC/DC power systems,in which large numbers of nonlinear electrical and electronic devices are employed.As a consequence,substantial harmonic currents will be generated during system operation,posing a non-negligible harmonics pollution problem to the power grid.With the launch of large-scale metro development initiatives,the search for an efficient and reliable harmonics harnessing scheme capable of improving the power quality of metro power supply systems has become a hot research topic in present scientific research.Inductive filtering technology is a novel filtering technology developed by Hunan University in a series of major scientific research projects.Based on the inductive filtering technology,a novel design scheme for rectifier units is proposed for application in metro power supply systems.The main contributions are the following:The existing harmonics harnessing schemes for metro power supply systems are analyzed and compared.Furthermore,the drawbacks of traditional filtering methods and the significance of applying inductive filtering technology to harness this harmonics problem are summarized.The structure and operation principles of metro power supply systems are introduced,followed by an analysis of the harmonic distribution of the major harmonic sources in the system(e.g.rectifier units).Multi-pulse rectifier technology is also addressed;in particular,the operating principle and harmonic characteristics of 24-pulse rectifier units are highlighted in the analysis.To address the problems of the current harmonics harnessing schemes used in metro power supply systems,a novel design scheme for rectifier units is proposed for application in metro power supply systems.The wiring scheme and operating principles of the new rectifier transformer are also explored.Moreover,based on the electrical impedance constraints of inductive filtering techniques and various other technical parameters,the electromagnetic load,major geometric dimensions,and various performance parameters of the transformer are calculated,thereby presenting in detail the transformer's electromagnetic design scheme.A mathematical model is constructed for the proposed novel rectifier unit,based on which the hybrid AC/DC load flow of the metro power supply system is calculated.Equivalent mathematical models for the harmonics of various components of the AC network are also developed.The harmonic load flow of the metro power supply system is computed,based on the model of the proposed new rectifier unit.A filtering scheme is designed according to the structural parameters of the novel rectifier unit proposed in this paper,and the parameters of the filtering device are calculated.Moreover,Matlab/Simulink software is used to simulate and validate both the traditional 24-pulse rectifier unit and the newly proposed rectifier unit.The simulation results remain basically consistent with those obtained from the harmonic load flow calculations,which demonstrates that the new rectifier model has achieved an overall harmonic suppression performance equivalent to that of the traditional model.