Doubly-fed induction generator (DFIG) as a hybrid of asynchronous and synchronous machines

With increasing concern over greenhouse gas (GHG) emission, more and more wind turbines are connected to electric power systems. Since many of these new wind farms employ doubly-fed induction generators (DFIG), power engineers find it is necessary to understand the characteristics of the DFIG better. This paper presents the DFIG as a synchronous/asynchronous hybrid. Like the synchronous generator, the real power characteristics are shown to depend on the rotor voltage magnitude |VR| and angle δ. Like the induction machine, the real power characteristics also depend on the slip s.