Grid integration of offshore wind farms using multi-terminal DC transmission systems (MTDC)

Abstract

This paper discusses the control flexibility and fault ridethrough capability of the bi-polar multi-terminal DC transmission system based on voltage source converters used for integration of large-scale offshore wind farms. Issues such as voltage support and short-term frequency stabilization of the AC network utilizing the stored energy in the wind turbine inertia and DC link capacitors are discussed. Regarding control flexibility, two aspects are presented: power sharing between the grid-side converters by any ratio, and provision of an alternative path for the power flow in case of a permanent DC fault or loss of one grid-side converter. In this investigation, the wind farms are based on fixed-speed wind generators, while the converters are modelled as a neutral-point clamped converter using the universal bridge. The investigation was conducted in Matlab/Simulink.

Modeling of Electric Components in Multi-terminal DC Distribution Network

“…Up to now, DC technology applied in the transmission network has been exploited a lot by many researchers around the world [1]- [3]. Multi-terminal direct current (MTDC) transmission systems based on voltage source converters (VSC) have been commercially available.…”

Architectures and Control for Multi-terminal DC (MTDC) Distribution Network-A Review

“…Up to now, flexible DC technology applied in the transmission network has been exploited a lot throughout the world both theoretically and practically [1]- [3]. Control strategies for MTDC networks are introduced in [4]- [6].…”

A DC fault clearance method for series multiterminal HVDC system

“…By far, many literatures have discussed the advantages of using voltage source converter (VSC) for MTDC application and concluded that VSC MTDC can provide significant benefit for transmission network, such as the decoupled control of active power and reactive power, the support to weak AC system, the black start capability and small footprint [7][8] [9], etc. However, nowadays the maximum capacity of a VSC HVDC line is still limited within 2,000 MW level whereas the line commutated converter (LCC) based MTDC takes advantages of low cost and large capacity of more than 7,000 MW per bipole.…”

“…The basic control method "current margin control" for parallel MTDC, was discussed in 1963 [7]. The early development of parallel MTDC technology is summarized by [10], in which the papers published in 17 years (1963-1980) had been reviewed.…”

“…In China, the feasibility of using LCC MTDC for long distance HVDC transmission has also been discussed [6] [13]. Recent study results showed that most of ultra-high voltage HVDC (UHVDC) projects to be constructed during the 12th Five-Year-Plan period can employ LCC MTDC technology [7].…”