Overview of electrical protection requirements for integration of a smart DC node with bidirectional electric vehicle charging stations into existing AC and DC railway grids

摘要

Distribution network operators (DNOs) and railway traction system operators (RTSOs) who will connect bidirectional electric vehicle charging stations (EVCSs) (treated as both load and source) to their power networks need a unified set of requirements for safe operation. However, such requirements are currently unavailable. Accordingly, the authors in cooperation with the Spanish national RTSO and the most important Spanish DNO have elaborated a unified regulatory framework of requirements for the interconnection protection systems and the earthing arrangement of a DC node used as a reference to feed bidirectional EVCSs, now under construction. This node connects a 0.4-kV AC secondary distribution network (SDN), a 25-kV AC railway traction system (RTS), a 3-kV DC RTS, a local distributed resource (DR) system, and two bidirectional EVCSs. The DR system includes both a photovoltaic PV system as well as backup storage systems (battery and supercapacitor). Thus, the DC node has all the potential interconnections to serve as a reference for requirements regarding the interconnection of bidirectional EVCSs.