Review of the comprehensive utilization of regenerative braking energy in alternating-current electrified railways

In the context of global decarbonization initiatives and the rapid advancement of electrified railways, the efficient utilization of regenerative braking energy (RBE) has emerged as a critical energy policy in China. RBE not only significantly reduces railway energy consumption but also offers substantial potential for providing auxiliary services to the power grid, enhancing the coordination, economic efficiency, and stability of both railway and power systems. In this paper, we first analyze RBE utilization strategies, including the optimization of train operation scheduling, energy storage technologies, energy sharing mechanisms, and energy feedback configurations. Then, from a macro perspective, the hierarchical structure of the RBE control system is explored. The upper-level energy management system of regenerative braking exhibits development trends based mainly on thresholds, optimization, and learning. Meanwhile, the lower-level converter control system tends to adopt strategies that improve the voltage balance and circulating current performance of the modular multilevel converter-railway power conditioner (MMC-RPC) while reducing the computational burden. Finally, based on existing theoretical research and practical engineering applications, rational suggestions are proposed to enhance the utilization efficiency of RBE. These recommendations provide strong support for the efficient utilization of RBE in alternating-current electrified railways (ACERs), as well as for technological innovation and economic development.