Fix links ramp up start limit

[lisazeyen]

Closes #592.

Changes proposed in this Pull Request

This PR should set the expected behaviour of ramp_limit_start_up and ramp_limit_shut_down
ToDos:

• activate ramping constraints also if only ramp_limit_start_up is defined and not ramp_limit_up
• modify constraint so that ramp_limit_start_up is working as intended

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Unit tests for new features were added (if applicable).
• Newly introduced dependencies are added to environment.yaml, environment_docs.yaml and setup.py (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.19% ⚠️

Comparison is base (bea1ce7) 78.35% compared to head (367a949) 78.16%.

❗ Current head 367a949 differs from pull request most recent head 075e07e. Consider uploading reports for the commit 075e07e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #691      +/-   ##
==========================================
- Coverage   78.35%   78.16%   -0.19%     
==========================================
  Files          26       26              
  Lines        6758     6760       +2     
  Branches     1466     1466              
==========================================
- Hits         5295     5284      -11     
- Misses       1151     1163      +12     
- Partials      312      313       +1     

Files Changed	Coverage Δ
pypsa/optimization/constraints.py	88.38% <100.00%> (-3.04%)	⬇️

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[FabianHofmann]

I am wondering whether the fill with 1 makes sense here, since this is in units of MW.

[lisazeyen]

no it has to be filled with then "p_nom". Thanks for pointing it out. I already corrected it but haven't pushed it yet. I am currently having troubles since the problem seems to be unbounded with the new formulation of the constraint

[matlawsky]

Hello, does present changes on this branch solve the ramp up limits problem ?