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 frequency-type 'parameter' this is simply a parameter value.

For frequency-type 'signal' it is a positive input signal.

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

This angle allows the definition of a rotating electrical**coordinate system**

for**AC three-phase models**.

Root-nodes defining coordinate-orientation will choose a reference angle theta_ref (connector-variable theta[2]) according to the parameter`ref`:

`theta_ref = theta if ref = "synchron"`(reference frame is synchronously rotating with theta).

`theta_ref = 0 if ref = "inertial"`(inertial reference frame, not rotating).

where

`theta = 1 :`reference frame is synchronously rotating.

`ref=0 :`reference frame is at rest.

Note: Steady-state simulation is only possible for`ref = "synchron"`.

`ref`is determined by the parameter`refFrame`in the following way:

**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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