Technology developments and plans to solve operational challenges facilitating the HVDC offshore grid

Abstract

This paper describes voltage source converter (VSC) offshore technologies for expansion of point-to-point transmission systems to HVDC offshore grids. Today several gigawatt wind farm projects are underway or have been proposed in the North Sea, Baltic Sea and Atlantic Ocean.These first offshore VSC stations has been installed on oil and gas platforms for power from shore in 2005 or using structures that are lifted on site for connection of wind farms in 2010. New and innovative modular solutions for converter offshore platforms in the gigawatt-range have been developed.As the offshore wind generation increases it makes sense to connect the offshore converters into a multi-terminal grid for better utilization of the transmission systems and connection to balancing power. The key technological cornerstones to plan and start building the first parts of HVDC offshore grids are available today and the gaps for deployment of a full-fledged offshore grid are outlined.

Offshore Wind Power Integration into Future Power Systems: Overview and Trends

“…Since 2005, VSC-HVDC technology has been used in offshore applications. It is based on IGBTs [122]. The main characteristics of the VSC-HVDC link are summarized as [123][124][125]:…”

Review of HVDC Circuit Breakers Topologies.

“…The CSC-HVDC system do not have the ability to independently control its active and reactive power and need high pass filters to eliminate the harmonics on the AC side of the network. Also, they lack the ability for power reversal capability because the voltage polarity has to be changed which is difficult to achieve [10]- [11]. This necessitated the development of an efficient and reliable system based on VSC-HVDC system with multiterminal grid.…”

“…This delay causes damage to transmission network and other power associated components thus necessitating a fast breaker based on DC technology. The DC current in DC breakers have no current zero crossing point thus making it difficult to interrupt the fault [11]. One of the traditional approaches for achieving current zero crossing point during the fault is the use of resonant current as shown in fig.…”

“…However, failure by the breaker to timely isolate the fault can be detrimental to both human being and the components being protected thus, hybrid CB continues to attract a lot of attention as recently witnessed in [19]. Further, ABB and ALSTOM have developed Hybrid HVDC CB prototypes with some considerable improvements in recent research [11], [20]- [21]. There are many available topologies of hybrid CB at various stages of development, but only two attract more attention.…”

Transient stability analysis of VSC HVDC transmission with power injection on the DC-link

“…Here are several examples: 300 MW, 350 kV Caprivi link of Namibia; 400 MW, 200 kV US-East Bay Oakland; 400 MW, 150 kV NordE.ON1 Germany; 350 MW, 150 kV Estlink Estonia Finland-Espoo; 200 MW, 150 kV Murray link Australia; etc. These two-terminal DC-links were generally not designed for the connection of distributed generators [8].…”