For dynamic simulations, the rotor speed of a DFIG needs be initialised externally because it is not directly coupled to the grid frequency. The rotor-side converter allows the machine to operate at variable speeds around the synchronous speed, meaning that the mechanical operating point is determined by external conditions such as wind speed and turbine dynamics. Since the DFIG electrical equations depend on the rotor speed through the slip, an initial speed value is required to determine the machine's initial electrical state.

Due to the above, the initialisation of an induction machine with the DFIG option differs slightly from the standard PowerFactory approach. The machine speed is initialised from the xspeed output signal. If the xspeed output signal is not connected, the speed is initialised to 1.2 pu. The same mechanical equations are used as for the standard induction machine.

If the mechanical equation is modelled separately and the built-in mechanical model is not used, the speed must be provided to the model via the speedIn input signal. In this case, the speedIn signal is also initialised using the value of the xspeed output signal.

Please also note that the xspeed output signal must be initialised in a model other than the DFIG control model to avoid creating an algebraic loop during DFIG initialisation.

Please refer to the PowerFactory wind turbine template "DIgSILENT DFIG WTG 2.5MW 50Hz" to see and analyse how the speed is initialised from the xspeed output.