Comparison of Energy Storage Configurations in Railway Microgrids

Energy storage systems (ESSs) that are composed of batteries and supercapacitors are increasingly being used as receptors for regenerative braking energy (RBE) in railway applications. These ESSs can be installed on-board the rolling vehicle, or off-board wayside, or mixed on-and off-board. This paper presents a comparison of three different ESSs topologies applicable in trains powered by a dc feed from substations with diode-based rectifiers. These substations cannot return RBE to the grid, requiring utilization of RBE by available receptive loads and ESSs connected to the dc power network. The dc power network is modeled as a dynamic dc micro-grid and this paper shows the impact of the ESS topology in the overall efficiency of a RBE recovery system. Maintaining the ESS components off-board provides the least overall energy consumption from a unidirectional substation. Although placing a supercapacitor onboard might intuitively appear to improve RBE utilization, the additional energy consumption to carry the ESS component mass reduces the benefits of an on-board system.