When decelerating or braking, a traction vehicle (train, tram or trolleybus) is feeding the regenerated braking energy back into the DC power network. Typically, if braking energy is not used by other vehicles in the network, it must be dissipated by the onboard braking resistors. Rather than having the braking energy be dissipated, the ENVILINE Energy Recuperation System (ERS) saves the surplus braking energy of the train by returning it back to the AC grid.

ERS is a modular, IGBT-based inverter system installed at the DC substation and connected in parallel with the existing diode rectifiers that can be scaled according to the customer’s needs. In addition, the ERS can improve the quality of the AC power network through harmonics and reactive power mitigation, and due to bidirectional operation it can offer support to the existing rectifiers through active rectification.

If connection to the AC grid is not available, then the ENVILINE ESS (Energy Storage System) stores the surplus braking energy and feeds it to the power line to assist the acceleration of the train. The system improves traction power quality and manages peak power demand; it can also be used as a standalone traction power system, permanently installed or mobile, to replace conventional grid-connected traction power systems. When used with batteries, ESS can also provide emergency power and generate revenues by participating in the local energy markets.

ABB installed a battery-based ENVILINE braking energy recuperation system in a substation of SEPTA in 2012 and has now incorporated Maxwell ultracapacitors in a new hybrid configuration to increase energy recovery efficiency and extend battery life.

In addition to reducing SEPTA rail vehicles’ consumption of grid-supplied electrical energy by 10 to 20%, the system enables SEPTA to provide frequency regulation services on the PJM Interconnection Network, a regional transmission organization (RTO) that coordinates the movement of wholesale electricity in all or parts of Delaware, Illinois, Indiana, Kentucky, Maryland, Michigan, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia and the District of Columbia.

By incorporating ultracapacitors, we will recover more braking energy, produce higher revenues from frequency regulation and extend battery life. The SEPTA model is the first of its kind in the world, going beyond the recovery of braking energy by also helping the electricity grid to be more stable and efficient with fast regulation support.

—Jacques Poulin, ABB’s product manager for energy storage and rail.