| China's electrified railway is the main source of harmonic in the power system. With the development of the railway, the problem will be more serious and draw more attention by engineers. In order to provide railway management with basic data, it is necessary to study the harmonic characteristics of locomotives and Electrical Multiple Units (EMUs).The characteristic of harmonic current for various existing locomotives and EMUs is studied in this paper. AC-DC electrical locomotives can be divided into five types according to their different main circuits. In this paper, the main circuits and their control principle of representative models are analysised in detail and the relationship between the locomotive operation conditions and the status of the main circuits are derivated. AC-DC-AC electrical locomotives and EMUs use four-quadrant converters. Thus main circuits of three topology four-quadrant converters are studied, including two-level, three-level and parallel two-level four-quadrant converters. The strategy of widely-used forecast current control is studied and the harmonic content of the current is also analyzed theoretically with double Fourier transform technique.In this paper, the simulation models of various locomotives are established by Matlab/Simulink. What's more, a kind of software is developed to simulate and analyze the harmonic current of the locomotives and EMUs. Based on the locomotive operation parameters calculated by traction software, it can simulate and analyze the amplitude,content,and phase of harmonic current.The currents of SS4G and CRH2 are measured in running railway. Compared with the simulation results, it shows that the established models have a higher accuracy.
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