Developing regional, radial DC grids and their interconnection into large DC grids

The development of future DC grids has high importance for future EU energy policy, but the technologies and DC grid topology are still uncertain. This article studies the concept of building large DC grids as an interconnection of regional radial DC systems. The radial topology enables very simple and robust DC system protection. It is not feasible to directly connect radial systems using DC cables because of requirements for protection system communication and associated delays. DC/DC converters offer possibility to interconnect two regional DC systems avoiding protection issues. Simulation tests are performed on detailed model of 2, 3-terminal radial DC grids interconnected using DC/DC converter. A fault on any radial cable is isolated using a local DC CB. A fault on interconnecting cable is isolated using DC/DC and a DC CB, without affecting operation of the other regional DC grid. It is concluded that the proposed method could be adopted to build very large DC grids which will satisfy high power transfer security standards.