Benefits of Operating a Four Terminal HVDC Network with a Normally Open Point

It is likely that any HVDC grids will evolve over time and will likely be multi-vendor and use several different technologies. This paper studies a four terminal network where the interconnecting link is operated as a normally open point. This allows the network to be reconfigured in the event of DC side fault, without the need for DC circuit breakers. The network uses the popular Modular Multi-level converter at one terminal and a fault tolerant converter at the other terminal. A simple cost benefit shows the economic advantage of the interconnecting link. The operation of this network is then verified through simulation for a normal operating scenario and a DC fault scenario. Keywords—HVDC, energy conversion, fault blocking converters, modular multilevel converter, multi-terminal DC