Current and power nodes

[FHell]

I wanted to document some thoughts of something we might want to implement going forward. Right now we make the modelling assumption that every node specifies a voltage, and the current then adapts to the voltages. We could also allow for nodes to specify currents and possibly powers.

A way to implement this would be to add a Holy-Trait to each node type that specifies whether the x[1:2] and dx[1:2] is a voltage or a current. Our lines then need to be made compatible with that. In practice this might mean that Static line has to have three implementations: V to V, V to I and I to I. When we assemble the grid we have to pick the right one based on the node type.

As an example, the V to V static line essentially looks like this right now:

I = Y * V

The I to I line would calculate the voltage as a function of the current:

V = Y^-1 * I

[luap-pik]

@FHell This seems to be a nice idea and relatively straight-forward to implement.
It might help a lot also with dynamic lines...

However, I'm not familiar with the concept of Holy-Traits for a type.
What is the difference to parametric types?
Also, we could extend the macro to provide functions vertextype(MyVertex) = :current and staticequivalent(MyVertex) = :PV (?)

Besides the V or I property, other traits should then be the corresponding static type (PQ, PV etc.)
for the conversion to power flow tools.