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This study focuses on the topic of energy efficiency for railway application. A case study extrapolated from a real system was approached. An entire railway infrastructure, constituted by an alternating current (AC) primary grid, a direct current (DC) railway system and some AC/DC railway electrical substations (ESSs), was observed. The considered system was represented to study the operation of the railway infrastructure in terms of energy. A method, based on an AC/DC power flow approach, was formulated to calculate the efficiency in the use of electrical energy, during the motion of a fleet of trains. The method reports the solution vector (i.e. the AC and DC voltages and currents) as a function of the scheduling of the railway service. The results of the numerical simulations focused on the energy amounts at the ESS. The discussion gives evidence to the impact of alternative operating solutions in terms of energy efficiency strategies.

Today, in the railway sector there is considerable interest in studying the best ways of exploiting train braking energy, in order to achieve a reduction in energy costs and better stabilisation of grid voltage. Among the various on-board or wayside measures proposed, one of the most promising solutions is based on using wayside energy storage systems (WESSs). A WESS is a storage installation which can be integrated into mass transit systems in urban areas as well as into long-distance railway lines. It can operate as a smart storage system able to provide relevant benefits in terms of recovering surplus regeneration braking energy, voltage stabilisation, reduction of peak power demand. For these purposes, an effective and flexible simulator is essential to provide all the elements needed to focus and compare feasible configurations and operations. This study examines the problem of introducing the WESS technology in real railway infrastructure. It proposes a method based on a simulator of the WESS system integrated into the infrastructure and carries out the results of dynamic simulations referring to real operating data of the system and vehicles. The results highlight the performance of the WESS in terms of energy and power exchange, also discussing economic aspects.

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

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