because the DFIG operates as a generator
maintaining or being fed with constant stator voltage [4].
Hence, stator voltage and stator current are either given (line
operation) or controlled (island operation) variables.
Two interpretations of the DFIG dynamic equations are
possible, depending on the state variables selected in the
model.Asynchronous machine model is obtained when selecting
the flux linked to the rotor currents [or back-electromotive
force (EMF) voltage] as a state variable.
Selecting the air-gap flux (or magnetizing current) as a
state variable invariably leads to an induction machine type
model. This can be demonstrated easily for steady state.
Both models give valuable insights on how the DFIG
works and can be controlled.
In steady-state and neglecting-stator resistance, the
stator voltage (7) reduces to