Voltage constraints for xward in OPF

[friederikemeier]

Hi,

@lschmelting and I discovered a problem....
If I run an OPF with a net with an xward, I feel like the xward it "out of control".
The problem is, that the internal generator in the ppc can not be controlled from within pandapower...
I can not set constraints, especially the voltage setpoint of the xward should be configurable from pandapower...
@rbolgaryn you may also want to join the discussion on how we are going to handle this?

I suggest, that the xward element gets max_vm_internal_pu and min_vm_internal_pu??? And we then write it into the ppc as voltage constraints for the internal bus?

Our old fashioned workaround à la

net.bus.min_vm_pu[net.xward.bus.at[0]] = net.xward.vm_pu.at[0] -1e-3 net.bus.max_vm_pu[net.xward.bus.at[0]] = net.xward.vm_pu.at[0] +1e-3

Does not work, as this only configures the constraints of the external bus.

[ghost]

Please check /pull/547.