fix_DC_cluster_issue

[p-glaum]

Closes #996

Changes proposed in this Pull Request

This PR fixes the bug described in #996. It guarantees that new links defined in links_tyndp.csv are only connected to AC buses. Before, this caused an error because we obtained a "meshed" DC grid in the model, which was not cleaned in the simplify_network script and led to wrong clustering.

Checklist

• I tested my contribution locally and it seems to work fine.
• Code and workflow changes are sufficiently documented.
• Changed dependencies are added to envs/environment.yaml.
• Changes in configuration options are added in all of config.default.yaml.
• Changes in configuration options are also documented in doc/configtables/*.csv.
• A release note doc/release_notes.rst is added.

[tgi-climact]

Thanks for the PR @p-glaum . When I looked up into the issue, I saw that filtering only AC buses resulted in different coordinates for the tyndp links. Have you checked this ? Is this a problem ? Thanks

[p-glaum]

In my opinion this should not make a difference, because so far as I know, in links_tyndp the geo coordinates are just taken roughly from Open Street Maps. Additionally, the exact location of the TYNDP links isn't clear anyway. We want to switch to OSM for the base network anyway, and then we will also have some new functionalities which can better handle those cases from #996. For example, if there is a new DC link for an offshore node which currently does not exist in the base network, base_network.py will add a new bus at the given location.

Have you found any big differences? Because usually, we aggregate the network anyway and do not solve it in high resolution.

[tgi-climact]

No big differences founded. I was just sharing my observations and related questions. Glad to read that it should not be a problem. Then the fix is quite simple.