The model **System** represents a global reference for the
following purposes:

It allows the choice of

- nominal frequency (default 50 or 60 Hertz, but arbitrary positive choice allowed)
- system frequency or initial system frequency, depending on frequency type
- frequency type: parameter, signal, or average (machine-dependent) system frequency
- lower and upper limit-frequencies
- common phase angle for AC-systems
- synchronous or inertial reference frame for AC-3phase-systems
- transient or steady-state initialisation and simulation
modes

For 'transient' initialisation no specific initial equations are defined.

This case allows also to use Dymola's steady-state initialisation, that is DIFFERENT from ours.

**Note:**the parameter 'sim' only affects AC three-phase components.

It provides

- the system angular-frequency omega

For fType Parameter this is simply a parameter value.

For fType Signal it is a positive input signal.

For fType Average it is a weighted average over the relevant generator frequencies. - the system angle theta by integration of
der(theta) = omega

- the reference angle
`thetaRef`for defining the coordinate-orientation:

`thetaRef = theta if refType == Synchron`(reference frame is synchronously rotating with theta).

`thetaRef = 0 if refType == Inertial`(inertial reference frame, not rotating). - the angle
`thetaRel = theta - thetaRef`

Root-nodes defining coordinate-orientation will have the connector variable

**Note**: Each model using **System** must use it with an
**inner** declaration and instance name **system** in order
that it can be accessed from all objects in the model.

When dragging the 'System' from the package browser into the
diagram layer, declaration and instance name are automatically
generated.

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