Multi-Terminal Multi-Vendor HVDC systems

The future electricity network will be characterized by a growing role of Multi-Terminal Multi-Vendor HVDC systems (or grids) within the current AC transmission networks, both onshore and offshore. Such innovative HVDC grids exploit the feature of VSC HVDC transmission, which reverses power through reversal of the current direction, without the need for voltage polarity reversal. This enables [1]:

  1. an efficient and safe use of innovative extruded cables – cheaper and more eco-compatible than traditional oil-paper insulated cables – on long-distance VSC HVDC sea/land cable lines;
  2. power reversal at intermediate taps, independently of the main power flow direction.

This latter is the reason why, aiming at reducing the costs and improving the reliability of VSC-HVDC links, VSC Multi-Terminal HVDC (MTDC) grids have been introduced (Figure 1). Compared to the traditional “two-terminal” – or point-to-point – HVDC transmission, MTDC grids consist of more than two VSC stations connected through a DC link, allowing the connection of all renewables (e.g. wind farms) and grids within reach of a transmission network and in turn increasing the flexibility and reliability of transmission.

Multi-Terminal VSC HVDC extruded cable transmission system configuration
Figure 1. Multi-Terminal VSC HVDC extruded cable transmission system configuration. From [2].

Differing from a point-to-point HVDC system, it is more challenging to design an MTDC grid and ensure the stable interoperability among converter systems, especially when the converters are manufactured from different vendors, thereby leading to a Multi-Terminal Multi-Vendor (MTMV) HVDC grid [3].

The READY4DC Project (https://www.ready4dc.eu/), supported by Horizon Europe, has created and engaged a community of experts that is assessing and giving recommendations on the major technical and legal aspects of designing and building an interoperable MTMV DC grid, to prepare the ground for the development of the first MTMV HVDC project in Europe. The NEWGEN consortium is cooperating with the READY4DC community, in particular as for reviewing White Paper 1 on modelling, simulation framework and data sharing for MTMV HVDC interaction studies and large scale EMT simulation.

References

[1] Bahrman, M.P.; Johnson, B.K. The ABCs of HVDC transmission technologies. IEEE Pow. Ener.Mag. 2007, 5, 32–44.

[2] Mazzanti, G. Issues and Challenges for HVDC Extruded Cable Systems. Energies 2021, 14, 4504. https://doi.org/10.3390/en14154504

[3] Y. Liao, H. Wu, X. Wang, M. Ndreko, R. Dimitrovski and W. Winter, “Stability and Sensitivity Analysis of Multi-Vendor, Multi-Terminal HVDC Systems,” in IEEE Open Journal of Power Electronics, vol. 4, pp. 52-66, 2023https://doi.org/10.1109/OJPEL.2023.3234803

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