Research on the Switching Process and Unanticipated Transient Event for Repurposing an AC Cable with DC-link in Distribution Network

This paper presents new approaches to determine the technical advantages of the switching operating, mainly in DC mode, due to any unanticipated transients, such as voltage dips, in a FDCL system. Thus, while using the DC operation voltage dip caused by either a fault in the upstream or downstream networks can be mitigated. In the case of voltage dips, the Voltage Source Converters (VSCs) must be able to ride-through the events to avoid a system short-interruption from a transient event. The aim of this paper is to broaden current knowledge for the case of a dip at the MV/LV substation at the point common coupling (PCC), where the VCSs should work to maintain the DC-side voltage and potentially also feed in reactive power to the upstream fault in order to minimize the dip penetration. Having this in mind, the DC-link is used to maintain the network throughout these events, thus an upstream dip should not have whichever effect on the medium voltage distribution network or even trip the system through its philosophy protection. Moreover, this paper sheds new light on the switching operation and its advantages through performance tests conducted in a smart grid laboratory using the flexible AC/DC-link in MV level.