Electrical Storage for the Enhancement of Energy and Cost Efficiency of Urban Railroad Systems

Today’s city traffic is often congested, because of the large amount of vehicles in comparison to the available space. Moreover road transportation contributes to the urban pollution and greenhouse gas emissions. One solution in the urban environment is the use of tramways. The most important bonus comes from the inherent reversibility of electric drives: energy can be sent back to the electricity source, while braking the vehicle. This can be done by installing some storage device on-board trains, or installing them in one or more points of the supply network. This paper therefore draws some results about when these systems can be useful and how they can be controlled. In general, storage systems with the following variants can be considered:  Stationary supercapacitors.  Stationary high-power lithium batteries. When the storage system is constituted by a supercapacitor, it is mandatory to interpose between it and the line a DC/DC converter. When, on the contrary, it is constituted by a lithium battery, the presence of the converter can be avoided. This paper provides an evaluation of the variant based on stationary high power lithium batteries, in a realistic case study. Some rather general conclusions will be drawn from the proposed analysis.