Topology And Control Strategy Of Photovoltaic Power Generation Connected To Railway Traction Power Supply System

With the continuous development of low-carbon transportation,it is imperative to develop and utilize the solar energy resource endowment along the railway.The use of space resources along the railway to implement photovoltaic power generation can not only provide clean power for railway traction system,but also expand the consumption space of new energy power generation.With the continuous development of low-carbon transportation,it is imperative to develop and utilize the solar energy resource endowment along the railway.The use of space resources along the railway to implement photovoltaic power generation can not only provide clean power for railway traction system,but also expand the consumption space of new energy power generation.However,most of the research objects of PV grid-connection are three-phase symmetrical and asymmetric power grids,and little attention is paid to the grid-connection of PV on the load side,i.e.the traction side.To solve this problem,this paper studies the topological structure and current control strategy of the traction side of the PV connecting railway traction power supply system.The main contents are as follows:Firstly,aiming at the grid-connection problem of photovoltaic on the traction side,the structural design of photovoltaic connecting to railway traction power supply system from the traction side is studied.Railway topology is currently divided into four different traction power supply systems according to DC and AC,namely,low-voltage DC traction power supply system,medium-voltage DC traction power supply system,AC phase-divided power supply system and AC phase-in power supply system.There are different access modes for photovoltaic based on different topological structures.Finally,the railway topology structure of three-phase low-voltage AC bus based on V/V transformer is selected from the actual starting point and economy,implementation difficulty,installation position and utilization mode of regenerative braking energy are compared,which lays a foundation for the theory and simulation of the following chapters.Secondly,aiming at the problem of unbalance of power grid caused by negative sequence current generated by single-phase traction load,the control strategy of partial sequence current of photovoltaic connected to railway traction power supply system is proposed.The positive and negative sequence mathematical models of railway topological structure based on V/V transformer are established.The relationship between the positive sequence current of high voltage side,traction side and photovoltaic side is analyzed in the positive sequence network,and the relationship between the negative sequence current of high voltage side,traction side and photovoltaic side is analyzed in the negative sequence network,and the conclusion that single-phase traction load can be compensated by controlling the negative sequence current of photovoltaic side is obtained.Then,the forward coordinate system and reverse coordinate system are introduced to analyze the photovoltaic positive sequence current instructions in the forward coordinate system and the negative sequence current instructions in the reverse coordinate system,so as to obtain the photovoltaic inverter’s positive sequence current instructions in the forward coordinate system and the negative sequence current instructions in the reverse coordinate system.proportional integral(PI)controller is applied to implement negative sequence compensation of traction load.Finally,MATLAB/SIMULINK simulation platform was used to verify the effectiveness of the proposed partial current control strategy for connecting PV to railway traction power supply system.Finally,in view of the complexity of the control strategy,which requires dq decomposition,a phase current control strategy is proposed to connect PV to railway traction power supply system.The phase current model of railway topology based on V/V transformer is established,and the relationship between high voltage side,traction side and photovoltaic side current in railway traction network is analyzed.The conclusion that the phase current of photovoltaic inverter can be directly controlled to control the negative sequence current generated by single-phase traction load is obtained.Then the phase current command is obtained to realize the unified control of negative sequence compensation and grid-connected synchronization of photovoltaic inverter.Finally,MATLAB/SIMULINK simulation platform and RTLAB hardware in the loop experiment platform were used to verify the effectiveness of the proposed phase-divided current strategy for connecting PV to railway traction power supply system.