An Optimal Centralized Control Strategy for Regenerative Braking Energy Flow Exchanges in DC Railway Traction Systems

The growing concerns about environmental pollution and climate change focus on the need of improving the efficiency in railway systems. Being the urban rail transportation service characterized by repetitive starts and stops, regenerative braking is an attractive measure for reducing energy consumption. Typically, when Energy Storage Systems (ESSs) are not installed along the track or on board the train, the not-reversible Traction Power Substations (TPSs) significantly compromise the opportunity of recovering energy from the regenerative braking. In this context, the present work proposes an optimal centralized control strategy for energy savings and voltage regulation. The strategy is formulated in terms of a constrained optimization problem. The effectiveness of the proposed control strategy is assessed in the real case of the metro railway system of Naples (Italy). Numerical results point out that the daily reduction of energy consumption would be approximately 100 MWh, which accounts for about 40% of the daily energy supplied by the TPSs.