Benefits of asymmetric HVDC links for large scale offshore wind integration

The large remote offshore wind clusters that are planned in the North Sea will most likely be connected with a meshed HVDC grid. Power will mostly flow from the offshore wind clusters to shore, creating asymmetrical requirements for the HVDC links that will consist of several parallel HVDC systems. To realise an asymmetrical link, some of those systems could be designed unidirectional, resulting in possible changes and simplifications (especially to the protection system). Assessment of a future scenario has shown that 42% of the HVDC systems can only be operated unidirectional. The remaining systems could in theory be used both directions, but power flow optimisation has shown, that this will in many cases not happen. A first cost calculation has shown that almost 6% of the investment cost can be saved when asymmetric design is implemented. This indicates the need to consider asymmetric design and to develop unidirectional HVDC systems.