Opportunity Charging of Electric Buses Directly from a DC Metro Catenary and Without Storage

Abstract

A typical approach to harvesting the excess braking energy of a railway car has been to use a storage system. However, research momentum has been growing in the direction of integrating smart loads like EV chargers into traction networks, and this can offer a more efficient and economical solution to the harvesting of braking energy. This paper examines the case study of a segment of the Amsterdam metro grid with two 350kW integrated DC opportunity chargers for charging electric buses from the traction grid. Of the charging episodes investigated, none of them broke the minimum line voltage requirements of the grid. They managed to greatly offset any additional line losses that they had caused by a successful recuperation of up to 1212kWh per day, depending on the charging duration. In all four schemes, about 22.8% of the picked-up charging energy of the buses per day came from harvesting otherwisewasted metro braking energy.