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HVDC Network Topologies

HVDC network can be classified into two categories:

1. Point-to-point HVDC network

2. Multi-terminal HVDC network

Radial HVDC network
Meshed HVDC network

1. Point-to-Point HVDC Network

At the starting stage, the HVDC network is used as point-to-point HVDC configuration. In this network, the HVDC link is connected between the two buses. The point-to-point HVDC network can also be called a two-terminal HVDC network. However, all the point-to-point HVDC network is not a two-terminal HVDC network. For example, if both terminals are connected or located at the same bus (back-to-back HVDC scheme), then the two-terminal HVDC network is not a point-to-point HVDC network. Fig. 1 shows the point-to-point HVDC network.

The advantage of this configuration is a simplified protection scheme. However, the power flow can be interrupted if any fault/outage occurs in a DC line/converter. Therefore, this point-to-point network provides less flexibility and reliability.

Fig. 1. Point-to-point HVDC network.

2. Multi-terminal HVDC Network

The multi-terminal HVDC network uses different topologies such as radial and meshed networks. It is more suitable for power transfer in the latest technology like VSC-based HVDC systems because building the multi-terminal network is very easy since the VSC maintains the constant DC voltage even if the power direction changes. The multi-terminal configuration gives less cost and more reliability than the point-to-point network since it requires a lesser number of terminals. It can be used to transfer the power even under the faulty situation in any one of the poles/converters.

2.1. Radial HVDC Network

The radial HVDC network configuration is shown in Fig. 2. The radial network is a connection with no loops and at least 3 terminals. The radial network looks like a star connection.

Fig. 2. Radial HVDC network.

2.2. Meshed HVDC Network

Fig. 3 shows the meshed HVDC network configurations. The meshed network has at least one mesh connection with more than two terminals. The meshed connection of the multi-terminal network gives more reliability and flexibility than the radial network. Therefore, the meshed connection is the best option for the VSC-HVDC transmission of electric power from offshore wind farms to the onshore AC grid.

Fig. 3. Meshed HVDC network.

References

Van Hertem, Dirk, Oriol Gomis-Bellmunt, and Jun Liang. HVDC grids: for offshore and supergrid of the future. John Wiley & Sons, 2016.
Chaudhuri, Nilanjan, et al. Multi-terminal direct-current grids: Modeling, analysis, and control. John Wiley & Sons, 2014.
Bucher, Matthias K., et al. "Multiterminal HVDC networks—What is the preferred topology?." IEEE Transactions on Power Delivery, 2013.
Vrana, Til Kristian, et al. "Definition and classification of terms for HVDC networks." CIGRE Science and Engineering, 2015.
Gomis-Bellmunt, Oriol, et al. "Topologies of multiterminal HVDC-VSC transmission for large offshore wind farms." Electric Power Systems Research, 2011.