| Chinese rapid development of high-speed railways has surpassed the total mileage of developed countries for decades of high-speed railways in just a few years.Continued expansion of the road network coverage in the central and western regions and perfecting the railway network construction in Tibet and Xinjiang are the requirements of Medium and Longterm Railway Network Planning during 2016 to 2025.The power grids in the central and western regions of China are weak and the system is underdeveloped.Negative sequence problems in the power system is caused by single-phase loads.In addition,the topography of the central and western regions of our country is mostly plateaus,with high altitude,thin air,low air pressure and harsh natural environment.Permafrost is widely distributed along the line,ramps and tunnels are long and numerous,railway and power lines are difficult to erect.There are electrical phase separation,so there may be hidden dangers of trains stopping in areas without electricity.The power supply system of the traction substation group is equipped with a centralized compensation device and the electrical phase separation is eliminated,which can solve the problem of negative sequence and electrical phase separation in railway construction in areas with weak power sources,and improve its power supply reliability and train operation safety.In this paper,based on the power supply system of the traction substation group and combined with the reactive power compensation scheme,the compensation scheme and main topological structure of the centralized compensation device are carried out,so that the negative sequence meets the requirements of the national standard.Based on the power supply system of the traction substation group,a reactive power compensation scheme is adopted in this paper to study the working principle and compensation principle of the compensation device based on the YNd11 compensation transformer.In addition,two-port compensation scheme and three-port compensation scheme are adopted for different power factor conditions.The compensation principles of the two schemes are theoretically derived.Based on this,the current detection and compensation current command value are calculated by the phase detection method.In order to meet the large-capacity requirements of the centralized compensation device,modular multilevel converter is used in this paper to study and compare the main topological structure of the main circuit and the sub-module circuit;the main working principle of the single-phase MMC-SVG device is studied,The modulation mode and voltage equalization control strategy of the device are combined with control strategy of the compensation current detection.According to the measured data of the traction load and using the Matlab/Simulink simulation platform,simulation models of the two kinds of compensation schemes are built to verify the feasibility of the compensation device and the rationality of the control strategy selection. |
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