Review on DC collection grids for offshore wind farms with high‐voltage DC transmission system

Abstract

Traditionally, the network composition of offshore wind farms consists of alternating current (AC) grid; all outputs of wind-energy conversion units (WECUs) on a wind farm are aggregated to an AC bus. Each WECU includes: a wind-turbine (WT), a generator and a power transformer. For a DC collection grid, all outputs of WECUs are aggregated to a DC bus. The transformer in each WECU is replaced by a converter which is more compact and smaller in size compared with the transformer, thus simplifying the wind farm structure. The use of AC offshore grids instead of DC offshore grids is mainly motivated by the availability of protection devices. Efficient solutions to protect DC grids have already been addressed. Presently, there are no operational DC wind-farms, only small-scale prototypes are being investigated worldwide. Therefore, a suitable configuration of the DC collection grid, which has been practically verified, is not available yet. This study discussed some of the main components required for a DC grid including: the WT-generator models, the control and protection methods, the platform structure, and the feeder configurations. The key component of a DC grid is the converter; therefore, this study also reviews some topologies of converter suitable for DC-grid applications.

A Review on MVdc Collection Systems for High-Power Offshore Wind Farms

“…summarizes the OWPP collection system options with their advantages and disadvantages. Due to additional benefits such as lower losses, zero reactive power compensation, elimination of 50/60 Hz bulky transformers, lightweight and reduction in the size of power electronic converters MVdc technology will be a promising option for future OWPP collection systems [12]- [14]. Thus, this paper attempts to review suitable MVdc collection systems and dcWT topologies for future large scale OWPPs.…”

“…However, reliability of these two configurations at the cluster level can be increased by introducing additional dc/dc converters at the expense of capital investment. The interarray cable network can be configured as single-sided radial feeder, bifurcated-radial feeder, single-sided or double-sided ring feeder as discussed in [12].…”

Impact of Electrical Topology, Capacity Factor and Line Length on Economic Performance of Offshore Wind Investments

“…As for a high voltage transmission system, DC topology for collection system is being discussed to be an alternative to AC collection system as it may reduce cable losses and costs. The improvement in DC control and protection device technology also will make the DC collection system more attractive over AC collection in which the control and protection devices are well established and used [15]. Currently, there are no OWF with DC collection systems but a few prototypes are being investigated [15,16].…”

“…The improvement in DC control and protection device technology also will make the DC collection system more attractive over AC collection in which the control and protection devices are well established and used [15]. Currently, there are no OWF with DC collection systems but a few prototypes are being investigated [15,16]. A detailed cost analysis is therefore needed for both complete AC and DC collection and transmission systems since the cost depends on various parameters such as rated power, wind capacity factor, losses, distance from the shore and so forth [5,12].…”

“…While the above-mentioned studies focus on the transmission system, few studies have presented the DC collection system for OWF [15,24]. Possible designs, topologies, converter types and platform configurations are given to provide an inside for the possible usage of DC collection systems together with the HVDC transmission [15]. In Reference [24], a new converter topology was proposed to decrease losses within the DC collection system as an alternative to AC topology.…”