REGCA Documentation + More Function Primitives

[lukelowry]

Description

Draft of REGCA machine-like and REECA exciter-like IBR model specification, which relies on new function primitives in CommonMath . Helps standardize the smooth-ization of the common model components and increases readability. These primitives will be used extensively in the upcoming IBR models.

@abirchfield @BSzymanowski I needed this for the theory section of the HICSS paper ASAP and realized I could construct most of the noncontinuous features with a ramp function primitive. I changed the variable names because the diagram doesn't match my expectations. Let me know what you think, and compare it against any progress you have made on this model, please

@nkoukpaizan Enzyme is starting to make sense to me, so I think I made changes correctly. Please check my CommonMath work!

Proposed changes

• REGCA Model Documentation
• REECA Model Documentation
• CommonMath Primitive functions
  • ramp
  • qramp
• CommonMath Derived functions
  • min
  • max
  • linseg
  • clamp
  • slew
  • antiwindup
• IEEEST refinement using new CommonMath, but also removing the output limiter, which seems to be incorrectly documented in the Power World reference. The functionality appears unclear and inconsistent across different sources. Many do not include it on the IEEEST, so I removed it since it was proving difficult to comply with Enzyme.

Checklist

• All tests pass.
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows GridKit™ style guidelines.
• There are unit tests for the new code.
• The new code is documented.
• The feature branch is rebased with respect to the target branch.
• I have updated CHANGELOG.md to reflect the changes in this PR. If this is a minor PR that is part of a larger fix already included in the file, state so.

Further comments

All in preparation for the two IBR models REGCA and REECA, which I have working implementations for.

[BSzymanowski]

Looks good to me.

[nkoukpaizan]

I still have to go through some of the math and related tests. A few preliminary comments.

[lukelowry]

@abirchfield Clear for your review!

Adding these primitives has been very helpful for readability and will help when we fine-tune the solver for all models with state-space discretization unilaterally.

[pelesh]

@lukelowry, for faster reviews in the future, I suggest you break PRs like this in single-topic PRs.

[lukelowry]

@pelesh That is my fault. For various reasons, it turned into a general cleanup + a reference for another branch of mine, so I let it grow. I'll do better with the rest!

[nkoukpaizan]

Mostly looks good to me. A few comments on the common math tests. Please try to minimize the number of hard-coded values.

I would like @abirchfield to approve the new model documentations.

[lukelowry]

@nkoukpaizan Complete, I am glad you pushed back on the tests because they are more readable now. Just awaiting @abirchfield