An approach to recover braking energy of a tram

This paper describes an approach to recover braking energy of a tram, supplying it back to the overhead lines via the substation DC link. Usually, the trams braking energy is only recovered when another tram is available and demanding energy in the same substation line. Otherwise, the energy is dissipated in a braking resistor contributing to the energetic inefficiency of the system. With the proposed system it is intended to recover the braking energy, which will be stored in capacitive banks. The core bank uses supercapacitors and is basically a Marx generator operating within rated conditions. The system has a second set of capacitors, corresponding to a second stage, and is used when the energy stored is very low and the system cannot provide the rated voltage (720V DC, in this case), at the DC link. With the proposed approach the discharge of these two stages, in order to inject the stored energy in the DC link, is primary made via a DC/DC. Anyway, the system can also provide 230V AC 50 Hz to auxiliary functions, as for instance, powering control and supervision systems, substation lighting, intersections command, dehumidification system, etc., through a DC/AC converter.