The class implements a model of a simple proportional governor with saturation.
If fixInitialControlledVariable = true, an initial
equation is added to ensure that the mechanical power output
PMechPu is equal to its start value
PMechPuStart. In order to fulfill this condition, the
initial value of the reference signal should be free, so that the
Modelica tool can back-compute it automatically. For this purpose,
the PowerGrids.Controls.FreeOffset
block should be used to generate the reference signal to be
connected to the VrefPu input.
In case the condition PMechPu = PMechPuStart cannot
be fulfilled without violating the controller saturations, then an
alternative initial condition is enforced, which prescribes the
saturation block input so as to obtain a certain degree of
oversaturation oversaturationPu. This allows to
back-compute a unique initial value of the reference signal, which
is of course dependent on oversaturationPu and hence
somewhat arbitrary.