Two-Stage Power Flow Management for Flexible Section Posts of Electric Railways Considering NSC and Voltage Control

This paper proposes a flexible section post (FSP) that integrates unified power flow controllers, photovoltaics (PVs), and energy storage systems (ESSs) into existing split-phase electric railways (ERs). This FSP provides more spatial and temporal power flexibility for ERs than existing FSP schemes. To reduce the complexity of the operational constraints of the proposed FSP, an active and reactive power flexibility model is derived. Then, a two-stage power flow management strategy is proposed, which fully utilizes the power flexibility of the FSP to achieve multi-objective operation. The first stage optimizes the output power of ESSs and the active exchange power between the FSP and tied TSSs. It aims to utilize PV and regenerative braking energy and reduce the maximum power demand of tied TSSs. The second stage optimizes the reactive exchange power between the FSP and TSSs to stabilize traction network voltages. Furthermore, an exchange power-based NSC constraint is employed to prevent the exchange power from exacerbating the negative sequence current (NSC) of tied TSSs. A series voltage magnitude-adaptive exchange power variation dynamic constraint is designed to enhance system dynamics while ensuring the operational constraints of the FSP. Finally, the feasibility of the proposed scheme is verified through hardware-in-the-loop tests.