A New Type DC Traction Power Supply System Based On DC-DC Converter

At present, the distance between DC traction power supply system and transformer substation is generally 1-4 km, Under the influence of contact line voltage drop, power distance can’t be extended, which leads to transformer substation have to be constructed intensively, all of these factors result in the huge cost of investment and more area occupied by the equipments. What’s more, the subway operation load will be greatly increased during rush hour, traction electric network current will increase a lot at this point, contact line voltage drop seriously, the system is most likely not able to provide the power required for the traction load. Therefore, In this research, a new type DC traction power supply mode based on DC-DC converter is proposed for these problems.According to the research and design of the new type DC traction power supply system, the main research works completed are as follows:Firstly, taking DC 1500V traction power supply system of city track as the research object, based on the analysis of the external characteristics of multi-pulse rectifier unit, the detailed calculation process of ideal voltage source and equivalent resistance of Thevenin’s equivalent circuit in the first to third section of multi-pulse rectifier unit working is analyzed, and the corresponding curves are plotted.Next, according to the structure of 24-pulse rectifier unit, the simulation model of typical DC traction power supply system is built in Matlab/Simulink, the main structure and technical parameters of the system are determined, and the simulation parameters are set up. The key indexes of DC traction power supply system are simulated and analyzed under certain operating conditions.Then, a new type of DC traction power supply system based on DC-DC transformation device is proposed. Adding another set of 24-pulse rectifier unit in transformer substation, keeping the original rectifier unit output voltage DC 1500V unchanged, then connecting negative electrode of new rectifier unit output voltage with positive electrode of the original rectifier unit output voltage in series, and output of DC 3000V. Adding a set of DC-DC transformation device controlled by PID control system in the middle of the two substation, the device transforms DC 3000V into DC 1500V and achieve gird connected power supply. This paper describes the working principle and the overall structure of the system, the DC-DC converter-alternating series-parallel connection multi-Buck DC chopper circuit and its control system required by the system are designed. The corresponding simulation model is built in the Matlab/Simulink simulation environment, and the simulation analysis is carried out. At the same time, the modeling and simulation of typical DC traction power supply system are done. The effectiveness of new type DC traction power supply system in the aspects of extending supply arm distance and improving power supply proposed in this paper could be validated by comparing.Finally, the modified new type DC traction power supply system based on DC-DC transformation device is proposed. Raising the original rectifier unit output voltage to DC 6000V, then transforming DC 6000V into DC 1500V by DC-DC transformation device in the substation. At the same time, Adding a set of DC-DC transformation device controlled by PID control system in the middle of the two substation, the device transforms DC 6000V into DC 1500V and achieve gird connected power supply. This paper analyses the working principle and the overall structure of the system. The multi-Buck DC chopper circuit and its corresponding control system are designed, the corresponding simulation model has been set up. The effectiveness of modified new type DC traction power supply system under certain conditions in the aspects of extending supply arm distance and improving power supply could be validated by comparing.