ABSTRACT
There are two main types of induction machines: squirrel cage machines, with rotor windings short circuited, and wound rotor induction machines, with accessible slip rings that can be either short circuited or connected to an external circuit. Wound rotor machines are used in applications where it is desirable to influence the rotor circuit keeping the stator supply constant. Before the advent of semiconductors, external resistors were used to control the slip and, consequently, power was lost in those resistors. By using power electronic converters it is possible to recover such slip power. Thus, a wound rotor induction generator (WRIG) with power electronic converters, i.e., fed on both stator and rotor, is called a doubly-fed induction generator (DFIG).
