These interconnections can link separate power systems within a country, or connect the national grids of separate countries. Coupled electricity markets require stable, controlled power flows for electricity trading to work effectively, or at all and this is obtained using HVDC technology.
Electrical networks in separate countries can evolve quite differently, and may have very different standards and technologies. DC is the only possible technical solution when interconnecting energy markets that operate at different frequencies (asynchronous), or are otherwise incompatible, allowing them to exchange power without requiring the tight coordination of a synchronous network.
Furthermore, HVDC interconnections help to reduce system losses, increase transmission capacity, improve power quality and helps to integrate more renewable power into the energy mix.