Joint Sizing Optimization Method of PVs, Hybrid Energy Storage Systems, and Power Flow Controllers for Flexible Traction Substations in Electric Railways

Flexible traction substation (FTSS) integrates PVs, energy storage systems (ESSs), and railway power flow controllers (RPFCs) into the existing split-phase traction substation. It is a vital solution in advancing electric railways towards a low-carbon, efficient, and grid-friendly future. To improve the techno-economic performance of FTSSs, this paper proposes a sizing method to jointly size PV, RPFC, and battery-ultracapacitor hybrid ESS (HESS). Firstly, a flexible operation model of FTSS is established. It fully uses the capacity of RPFCs for improving the three-phase voltage unbalance and average power factor, thus, reducing the capacity requirements of RPFCs. Next, a linearized approach is developed for estimating battery aging affected by battery cycles, depth of discharge, state of charge, and calendar time. It facilitates obtaining battery sizing with relatively accurate life evaluation in sizing optimization. Then, a joint sizing optimization model of PV, HESS, and RPFC is established to minimize the total annualized investment and operation cost of an FTSS, and it is formulated as mixed-integer second-order programming. Finally, case studies show that the proposed method can optimize the total annualized cost of FTSSs while ensuring efficient energy utilization and improvements of the three-phase voltage unbalance and average power factor.