Recuperation of Regenerative Braking Energy in Electric Rail Transit Systems

Electric rail transit systems are large consumers of energy. In trains with regenerative braking capability, a fraction of the energy used to power a train is regenerated during braking. This regenerated energy, if not properly captured, is typically dumped in the form of heat to avoid overvoltage. Finding a way to recuperate regenerative braking energy can result in substantial economic as well as technical benefits. Regenerative braking energy can be effectively recuperated using wayside energy storage, reversible substations, or hybrid storage/reversible substation systems. In this research study, we compare these recuperation techniques and investigate their application in New York City Transit (NYCT) systems, where most of the regenerative braking energy is currently being wasted. We have developed a detailed transient model to determine the applicability, feasibility, and pros and cons of deploying wayside energy storage, such as batteries, super capacitors or flywheels. This model has been validated using real measurement data on the 7-Line (Flushing), including:1) speed, current, voltage, power and energy train profiles; and 2) 24-hour interval metering data at substations. The validated model has been used to analyze and compare various ESS technologies, including Li-ion Battery, Supercapacitor and Flywheel. In addition, we have developed detailed transient models for reversible substations. A reversible substation, also known as bidirectional or inverting substation, provides a path through an inverter for regenerative braking energy to feedback to the upstream AC grid. This energy can be consumed by AC equipment within passenger stations (e.g., escalators) or fed back to the main grid based on legislations of the electric distribution utility. This study will provide crucial technical as well as financial guidelines for various stakeholders while making investment decisions pertaining to regenerative braking energy