Implementation of Active Power Substation for Harvesting Regenerative Braking Energy in Italian 3 kV Railway Systems

In line with the overall goals of EU climate commitments and railway operators, the reduction of CO2 emissions and the development of more eco-friendly transport systems with increased energy efficiency have become paramount. This paper focuses on the utilization of regenerative braking energy (RBE) and explores the potential of adopting active power substations as a solution. Active power substations enable bidirectional power flow, facilitating the feedback of RBE into the upstream grid. The paper presents a case study of the Italian railway system, which operates on 3 kV DC voltage and currently utilizes diode rectifiers in its traction substations. This configuration hinders power reversibility and prevents RBE, resulting in the wasteful dissipation of electric energy through braking rheostats. To overcome this limitation, the paper proposes a bidirectional electric substation configuration based on NPC parallel-connected converters. A control strategy is proposed and simulation results are provided to demonstrate the feasibility and benefits of the proposed approach.