Techno-economic sizing of auxiliary-battery-based substations in DC railway systems

Auxiliary-battery-based substations (ABSs) can enhance conventional railway feeder systems. In particular, ABSs make dc feeders located in areas far from the ac grid able to power high-performance passenger and freight trains and store their braking energy. This paper proposes a techno-economic method to define size, position along the track, and control parameters of an ABS, with the goal to minimize the annual cost of energy. Our approach takes into account the replacements of battery modules within the ABS's expected lifetime in order to reduce costs. Numerical simulations are carried out assuming a new-generation high-performance train on a real Italian 3-kV dc railway system equipped with one ABS. Although, in some cases, ABSs are already cheaper solutions compared to new traditional substations, the proposed sizing method allows obtaining a further reduction in the ABS cost.