Interesting to know, thank you. They seem to mostly use this to adjust the frequency of the induced current in the stator, as they control the rotation speed of

Interesting to know, thank you. They seem to mostly use this to adjust the frequency of the induced current in the stator, as they control the rotation speed of a "virtual rotor" (rotation of the rotor + rotation of the magnetic field around the rotor). That's indeed similar, but in the wind turbine use-case, the stator is passive. A direct application could be to tune the torque/speed response, or improve motor weight by reducing the number of coils on one of the elements.