Using HVDC to interconnect async grids is very common.
This presentation is a nice deep dive on the situation in Europe: we are even building HVDC “corridors” embedded inside some of the sync grids. Pricey gear but valuable too!
HVDC corridors make sense because it's functionally impossible to build new overhead transmission lines anywhere, so operators are forced to bury the transmission lines. But buried AC transmission lines have terrible loss and are super expensive, buried HVDC lines are slightly less expensive (but require expensive terminal stations), and have much lower losses.
> it's functionally impossible to build new overhead transmission lines anywhere
This isn't really true, new overhead lines are being built all over the place. It definitely depends where they're being built and there is definitely strong opposition from councils in e.g. some parts of Germany, but see for example in the Netherlands there are definitely new overhead lines being built: https://www.tennet.eu/nl/projecten/provincies/groningen/eems...
That being said it's true that it's much more challenging than it used to be to get planning permission.
> we are even building HVDC “corridors” embedded inside some of the sync grids
We also have that here in Brazil; the Xingu-Estreito and Xingu-Terminal Rio HVDC links run in parallel with the high-voltage AC links. On the other hand, the Madeira HVDC link (https://en.wikipedia.org/wiki/Rio_Madeira_HVDC_system) is AFAIK normally disconnected from the AC grid on the generation end (it has a direct connection, probably used to start up the power plants, but normally uses a back-to-back HVDC converter instead of it).
Using HVDC to interconnect async grids is very common.
This presentation is a nice deep dive on the situation in Europe: we are even building HVDC “corridors” embedded inside some of the sync grids. Pricey gear but valuable too!
http://catedraendesa.us.es/documentos/jornadas_uimp_2015/201...