Bidirectional Energy Control in DC Railways with Renewable Energy Sources Integration and Reversible Substations

Electric railway systems (ERSs) are increasingly targeted for energy efficiency enhancements and renewable energy integration due to their high and continuous power demand. The integration of renewable energy sources (RESs) into DC railway networks, however, presents significant challenges in terms of stability, power quality, and control. A fundamental requirement for successful integration is the ability of traction substations to support bidirectional power flow, both for feeding the DC line from the AC grid and for injecting surplus energy such as regenerative braking energy (RBE) and RES output back into the grid. Conventional diode-based substations are inherently unidirectional and incapable of fulfilling this role. This paper investigates the application of bidirectional active traction substations (ATSS), utilizing interleaved IGBT-based PWM rectifiers, which enable controlled bidirectional power exchange. The proposed system is analyzed through a detailed study based on the Italian 3 kV DC railway network. Key power quality performance metrics are evaluated under different operating conditions, including varying train loads and intermittent RES generation. Simulation results using MATLAB Simulink together with experiments confirm that the ATSS architecture significantly improves power quality, enables stable and efficient integration of RESs, and enhances overall energy utilization in modern DC railway systems.