Ultracapacitor assisted regenerative braking in metropolitan railway systems

This paper investigates the use of ultracapacitors as an energy storage system for metropolitan railway systems. The basic concept is to take advantage of the energy generated during the braking process of trains, which is otherwise wasted and transformed into heat. A power system simulation was created as a tool to analyze the behavior of a stationary ultracapacitor bank connected to the Metro system. Ultracapacitor modules were dimensioned adequately, power electronic elements were adjusted and further a control system was established. Amongst others the simulation demonstrates the impact of varying the distance between ultracapacitors and traction power substation. Furthermore the dependency of the ultracapacitor's technical specifications on charging and discharging behavior is shown. The simulation allows a large number of parameters to be modified through the easy-to-handle user interface. A scientific method is provided to analyze ultracapacitor assisted regenerative braking of metropolitan railway systems. As an example the Metro of Medellín in Colombia is applied and rounded out by an estimation of economic viability.