.Spot.UsersGuide.Introduction.Frequency

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System and Autonomous Frequency

The frequency concept must fulfil several conditions.

• First it should provide a common system frequency (50 | 60 Hz) that is either
  (i) parameter specified, or more generally supplied as an input signal
  (ii) a dynamical variable of the model, determined by the involved generators feeding the network.
• Second it should allow handling several subsystems, each with autonomous frequency, within one common model.
• Third it must allow both transient and steady-state simulation, and related to that the definition of rotating reference systems.

A system angular-frequency omega is provided by the component 'System'. We have three choices:

a) Parameter system frequency.

a) Signal system angular frequency through signal input.

b) Average system angular frequency, obtained as weighted average over involved generators.

The corresponding system-angle theta is obtained by integrating

  der(theta) = omega

and is used within the sources (voltage- or power-sources, and inverters).
Note: within a variable-frequency concept, theta can not be replaced by omega*time.

We distinguish two main cases:

A) Case network-frequency.
All sources within a network-backbone have system-frequency (fType='sys').

B) Case autonomous frequency, independent of network frequency.
The sources within a network-backbone have either parameter- or signal-frequency (fType='par' or 'sig').
Frequency-independent sub-systems within one model can therefore easily be defined.

Note:
    omega is used for electrical angular frequency,
    w is used for mechanical angular frequency.

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