Optimal design of DC electrified railway stationary storage system

The improvement of the energy efficiency is a key issue for electrified railway systems in order to reach an increased competitiveness compared to other transportation technologies in terms of both costs and environmental pollution. An important step towards this direction has been made with the increasing development of storage technologies. The installation of stationary or on-board storage technologies, as well known, allows the recovery of the braking energy of the rolling stocks for increasing the energy efficiency of the whole system as well as improving the voltage profile. In the paper an optimization procedure is proposed for choosing in the planning stage the fundamental characteristics of a stationary storage device. The optimal parameters of the storage system can be determined by taking contemporaneously into account the energy saving aspects, substation current minimization and reduction of voltage drops along the feeder. The considered storage system is based upon a bidirectional DC-DC converter with ultracapacitors. A sliding mode control is implemented for tracking the optimal trajectory determined by the previously mentioned optimal technique. Numerical applications put in evidence the effectiveness of the proposed procedure.