Research On Harmonic Analysis And Simulation Of Electric Traction Systems

With the development of high-speed and heavy-load transportation vigorously, AC drive electric locomotives and EMU(electrical multiple unit)in the domestic large-scale on-line operation, electrified railway has become the main source of China’s power grid harmonics. In response to this phenomenon, the problems of electrified railway power quality need to be monitored, limited and governed timely. This paper focuses on the problem of harmonic characteristics of AC drive electric locomotives and EMU were studied. For EMU, the diode-clamped three-level pulse converter was used by CRH2, and two-level pulse converter were used by other models. In this paper, CRH2 and CRH5 were targeted as the research object, through the establishment of its network side converter model to analyze the distribution of the harmonics.Firstly, the drive system of electric locomotives and EMU are studied, at the same time the influence of harmonics on the traction power supply systems and locomotives also was studied. The working principle of the network side rectifier is elaborated, AC drive electric locomotive using pulse rectifier and DC electric locomotive using phase-controlled rectifier which generated harmonics differences are studied. The two-level, three-level circuit pulse rectifier structure working principle are elaborated respectively on focus. While the rectifier harmonic generation mechanism is analyzed in-depth, and the mathematical model of the net side current transformer harmonic current is established. Related to net side converter control technology was studied, and the transient and predictive current control of two direct current control strategies are analyzed in detail, also the midpoint potential problems inherent to the three-level pulse rectifier be analyzed, then put forward a kind of relatively simple pulse conversion method to solve the problem. At the same time multiplexed carrier phase PWM rectifier technology has been studied, and achieve the purpose of expansion and reduce harmonics. Using Matlab/Simulink simulation platform, CRH2 and CRH5 models of rectifier circuit simulation model are built, the net side current harmonic of output characteristic which in rated conditions, power and traction network voltage changes has been studied. Lastly, the correctness of the theoretical analysis is verified by simulation.Through theoretical analysis of these two kinds of converter can deduce the EMU harmonic influence to power grid as a whole. Which can provide a theoretical support for the inhibition of harmonic interference on the power grid for the next step.