This paper proposes an energy storage system (ESS) for recycling the regenerative braking energy in the high-speed railway. In this case, a supercapacitor-based storage system is integrated at the DC bus of the back to back converter that is connected to the two power phases of the traction power system (TPS). In order to ensure the suitability of the ESS in the TPS, the operation modes are classified by considering the load conditions of the TPS and the state-of-charge limit of the supercapacitor. Then, a master-slave control strategy with a central controller is proposed. In which, the central controller realizes the flexible management for all operation modes, by means of the state machine logic. Meanwhile, the master-slave control serves for coordinating the operation of the multiple converters according to the commands from the central controller. Finally, the capabilities of the proposed ESS are validated by sufficient experiments under different operation modes and the simulation based on the field data.

Regenerative braking energy (RBE) utilization plays a vital role in improving the energy efficiency of electrified railways. To date, various power flow control-based solutions have been developed to recycle the RBE for utilization within railway power systems (RPSs). In this paper, an overview of the state-of-the-art power flow control-based solutions for RBE utilization in AC electrified railways is presented. It provides a technical analysis of four primary power flow control-based solutions for RBE utilization, including power sharing-based, energy feedback-based, energy storage-based, and composite solutions. The critical architectures of power flow conditioners for each solution are analyzed in depth. Meanwhile, the power flow control strategies for these solutions are reviewed from the perspectives of power flow management and converter control. From the industrial point of view, the critical challenges associated with fault protection, economy, and environmental impact are discussed. In addition, future trends are comprehensively elaborated from internal and extended improvements. This comprehensive review provides an insightful understanding of the technology readiness, constraints, and perspectives regarding the power flow control-based RBE utilization in electrified railways, contributing to bridging the gaps between academic research and industry implementation.

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.

It is energy-efficient and grid-friendly to utilize regenerative braking energy (RBE) in electrified railways. However, considering the segmented structure of the railway power system, it is challenging to utilize the RBE between adjacent traction substations (TSSs). To this end, an RBE utilization method involving power sharing and storage is proposed in this paper. The proposed method is implemented on a sectioning post-energy storage system (SPESS) to coordinate RBE utilization between adjacent TSSs. To provide real-time power management and control for the SPESS, a centralized power flow control strategy is developed. Specifically, a two-stage power dispatch algorithm-based power management strategy (PMS) is designed in the central controller. A nonlinear optimization function is formulated in the PMS to determine the active power commands to maximize the RBE utilization and shave the power demand. It also calculates the reactive power commands based on residual capacity to stabilize the catenary voltage. The power flow control is implemented in the local controllers as per the power commands from the central controller. The feasibility of the proposed method is verified through hardware-in-the-loop experiments. The techno-economic superiority of the proposed method over literature methods is validated based on field load data-based comparison analysis.

The railway power conditioner-based energy storage system (RPC-based ESS) is a promising technology to improve the regenerative braking energy (RBE) utilization and power quality of ac direct-fed (25 kV) and AT-fed (2 × 25 kV) railway power systems. However, despite its benefits from the technical perspective, economic viability must be concerned in industrial applications. The capacity is one of the critical issues affecting ESS performance in technical and economic aspects. Therefore, this paper presents a comprehensive approach to designing the capacity for the RPC-based ESS by considering multiple objectives, including the RBE utilization rate, power quality standard, and net lifetime benefit. The proposed approach develops a technical-economic model for the RPC-based ESS based on variables such as the system capacity for RBE utilization and power quality improvement, lifetime cost, and electric charge-based benefits. Moreover, the master-slave control strategy is employed to control the RPC-based ESS to implement the capacity design objectives. Finally, the correctness and effectiveness of the proposed method are validated by sufficient tests based on field load data of a Chinese traction substation.

This article proposes an integrated regenerative braking energy utilization system (RBEUS) to improve regenerative braking energy (RBE) utilization in electrified railways. The proposed RBEUS uses a traction substation energy storage system and two sectioning post converters to achieve coordinated RBE utilization in three consecutive traction substations via power-sharing and storage, and the power quality can also be improved. A hierarchically coordinated control strategy is developed based on the operation principle to provide real-time power management and control for the RBEUS. In the system layer, a centralized power management strategy is designed for operation mode management and active power command generation. It uses a sequential quadratic programming-based algorithm to solve the objective function to achieve optimal RBE utilization under different operation modes. In the converter layer, local controllers of the RBEUS enable converters to respond to the active power commands from the system layer and reactive power commands generated by themself for power flow control. The effectiveness of the proposed RBEUS is comprehensively verified by using a hardware-in-the-loop experiment. Besides, a comparison analysis of the proposed RBEUS and literature methods is conducted to testify the superiority of the RBEUS. The feasibility of RBEUS implementation is also discussed from fault protection and economy.