id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
4041	Wrong structural singular equation system	Rüdiger Franke	somebody	"The current tunc release reports the following error for `PowerSystems.Examples.Spot.Introduction.SimulationSteadyInitial`:

{{{
Error: Initialization problem is structurally singular, error found sorting equations 
 78: $DER.lineB.i[3] = 0.0;
75: $DER.lineL.i[3] = 0.0;
14: $DER.lineR.i[3] + $DER.lineB.i[3] - $DER.lineL.i[3] = 0.0;
72: $DER.lineR.i[3] = 0.0;
 for variables 
 meter.i[1](63), voltageL.V(70), $DER.lineR.i[3](77), meter.i[3](61), transPh.y[2](72)
}}}

See
https://test.openmodelica.org/libraries/PowerSystems/files/PowerSystems.Examples.Spot.Introduction.SimulationSteadyInitial.err

The solution to the reported equations appears obvious, even though it is for some reason overdetermined: all involved variables are zero. Why does OpenModelica report a structural singular equation system?

Note 1: the model was working until August 29, see:
https://test.openmodelica.org/libraries/history/PowerSystems/PowerSystems-2016-08-29.html
The PowerSystems library changed around that time with the introduction of an enumeration for initialization options, replacing Booleans, see:
https://github.com/modelica/PowerSystems/commit/7a8310bc7d36daee96538c4b0da4634d4a43343d

Note 2: the AC3ph models use the dq0 representation. The third coordinate is zero unless there is an unsymmetry between the three phases. Many models are symmetric by definition: sources assign 0.0 to variables of the third coordinate; component models pass the 0.0 through and never mix the third 0-coordinate with the d- or the q-coordinate.


Can't OpenModelica generally eliminate resulting equation systems with the  rhs all zeros?
"	defect	assigned	high		Backend