Offshore DC grids as an interconnection of radial systems: Protection and control aspects

Abstract

Abstract-This article presents a topology for DC grids which enables very robust DC fault protection with moderate costs, good operating flexibility and simple controls. It is postulated that radial DC systems are best suited for limited-size local DC grids. Radial topology enables robust and fast protection selectivity using only local signals and exploiting the advantages of hybrid DC circuit breakers. To enable flexible expansion options to national/international systems, it is suggested to interconnect star points of radial systems using DC/DC converters. DC/DC converters enable inherent isolation of DC faults and provide firewall between radial DC grids. Each interconnecting cable is protected by a DC/DC at one end and a hybrid Circuit Breaker at the other end. The control options for DC/DC converter and the radial grids are analysed. A detailed simulation model of 6 terminal DC grid with 2-star points is presented. The PSCAD simulation results confirm DC fault isolation and good control performance of the proposed topology for a range of DC fault contingencies.

Converter topological and solid state protective device trade-offs for future shipboard MVDC systems

“…An MMC based PGM seems well suited for "Breaker-Less" architectures because there is complete control over fault current. This conclusion is supported by recent research into the allocation of fault mitigation to power converters in combination with hybrid SSPD in off-shore tied HVDC systems [18]. The downside to this approach for shipboard applications is that an equivalent MMC will be significantly larger in size/weight than the other topologies.…”

Evaluation of the Impact of High-Bandwidth Energy-Storage Systems on DC Protection

“…Increasingly popular solutions to overcome these limitations include the redesign of the converter to be more fault tolerant and the use of converter based current limiting to suppress fault [17,26,27]. The use of converter current limiting potentially reduces the speed requirements of the protection system enabling the continued use of standard AC side circuit breakers or electromechanical DC switchgear for fault clearance [17][18][19][20][21][22][23].…”

Directional current breaking capacity requirements for HVDC circuit breakers

“…Whilst when considering other converter topologies a different or more relaxed protection scheme may be appropriate [7], [16], [17], the results discussed in the following sections apply in part to each of the known published protection schemes for meshed HVDC cable networks implementing fault-feeding converters and DC CBs [2]- [5], [7].…”