Diagram of Doubly fed induction generator (DFIG):
DFIG can feed power through the stator as well as rotor to the grid. The stator is directly connected to the fixed frequency grid while rotor is connected via bi-directional back-to-back converters. If the generator is running super-synchronously (i.e. NR speed is greater than NS speed), the electrical power is delivered by both the rotor and the stator to the grid. If the generator is running sub-synchronously (i.e. NR speed is less than NS speed) the electrical power is delivered to the rotor from the grid. Generated voltage is 690 V AC. So it must be step up to 33 KV to connect to power grid.