Wayside energy recovery systems in DC urban railway grids

In modern electrified and rail-bound mass transit vehicles, a considerable part of the braking energy is still dissipated via resistors. This applies in particular to less connected and low frequented grid sections. For this purpose, wayside energy recovery systems can be used to store excess energy and release it during acceleration of nearby vehicles. They offer further advantages, such as a potential reduction in the power requirement of substations or additional safety and reliability. This paper provides an overview of actual demonstrations of various systems in public transport grids. The focus is on the most important technologies (namely: supercaps, flywheels, batteries and inverters), as well as the respective manufacturers and products. The achievable improvements, based on both real demonstrations and scientific studies, are identified and critically evaluated. Important points for a better assessment of the systems are worked out. A future forecast is given for each of the four technologies. (C) 2019 The Author(s). Published by Elsevier B.V.