Signal Bus Implementation

[lukelowry]

Description

This PR proposes an initial implementation of BusSignal. This is used to read/write data between phasor dynamics models, which is a necessary feature to implement governor and exciter models.

Proposed changes

The following changes are proposed. Temporarily, the real value of the bus votlage $V_r$ is used for the input/output of $\omega$ and $P_m$ for Genrou and TGOV1.

• Sub-folder structure of bus types
• SIGNAL type added and supported by BusFactory pattern.
• BusSignal class source, header, README
• Declare signals in Governor header and Genrou header
• Setter functions for signals and handle case where no signal is provided in Governor source and Genrou source
• Use $P_m$ signal to improve initialization in Governor source by writing to $P_m$ signal in Genrou source
• Change governor unit test to use BusSignal instead of passing pointer in constructor
• Misc path includes modified to align with the folder structure of Bus Types

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.

Further comments

Unit tests are waiting until the general approach is approved by @pelesh and @abirchfield .

Unclear if specific read/write permissions need to be set for the signal. The BusSignal class has been implemented to treat signals similarly to network KCL, such that any model that has access to the signal can also read/write.

While this specific implementation is subject to revision, this will allow a governor example to be implemented.

[abirchfield]

Planning to return to this after implementing example with governor (without signals, requiring direct Genrou-Tgov1 connections that will later be deleted).

[lukelowry]

Needs rework, deleting branch.