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.

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.

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.

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.