[feature] Support of angle difference constraints

[SimonUlm]

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Feature Type

• Adding new functionality to pandapower

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Problem Description

Pandapower does not support angle difference constraints (in the context of PF and OPF). However, Matpower and Pypower do. This leads to an unexpected behaviour:

1. Read in m. file (e.g. a case file of the PgLib_OPF library with net = pp.converter.from_mpc(file)
2. Execute OPF with pp.runopp(net)
   One would expect the result of an OPF with constrained angle differences, however, due to the conversion to and from the pandapower format, these constraints are lost and are not considered in the simulation.

Feature Description

I think it should be sufficient to include an entry angle difference (or similar) to the branch data frame. Matpower and Pypower include both ANGMIN and ANGMAX. However, they are usually the same (with opposite sign), such that one entry could be enough.
Then, the conversions from and to the pandapower format need to be updated.

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