Capacity optimization of the supercapacitor energy storages on DC railway system using a railway powerflow algorithm

The electric railway system is one of the most peculiar power systems of which the location and power of electrical load are continuously variable. The variance of the location and power of the vehicle changes the participation factor of each substation for the vehicle and the sign and magnitude of the load current, respectively. Especially, on the substation feeder, there is huge voltage uctuation generated by the regenerative energy due to the braking vehicles. This regenerative energy is closely related with the energy efficiency since the surplus energy cannot be utilized and dissipated in the resistor. To improve energy efficiency of the railway system and utilize the surplus regenerative energy, the application of energy storage has been studied. In this paper, a DC railway powerow algorithm considering storages is developed to analyze the railway system with storages and to calculate the optimal power and storage capacity of them. The Seoul Metro Line 7 is selected for the test system and simulated to verify the effect of storages. Also, the optimal power and storage capacity of each SCES is calculated.