Combined Active and Reactive Power Flow Control Strategy for Flexible Railway Traction Substation Integrated With ESS and PV

This paper proposes a combined active and reactive power flow control strategy for the flexible traction substation (FTSS). It fully uses the active and reactive power flexibility of FTSS to maximize regenerative braking energy (RBE) and photovoltaic (PV) energy utilization and improve power quality comprehensively. First, the active power flow optimization layer coordinates the active power outputs of the back-to-back converter (BTBC) and energy storage system to maximize the utilization of the available RBE and PV energy and balance the active power outputs of the traction transformer. Meanwhile, it controls PV output to limit the surplus energy injected into the utility grid further. Then, the model predictive control (MPC)-based reactive power flow optimization layer employs the spare capacity of BTBC to optimize the reactive power flow to improve the multiple power quality issues further, including negative sequence current (NSC), effective power factor (EPF), and traction network voltage fluctuations. To establish the MPC optimization problem, the NSC, EPF, and traction network incoming voltage sensitivity matrices with respect to the reactive power outputs of the traction transformer are first derived. Finally, the hardware-in-the-loop experiments, based on the data measurement from a high-speed railway traction substation, verify the effectiveness of the proposed strategy.