Doubly-fed induction generators (DFIG) in wind turbines

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Wind turbines based on DFIG have the stator windings connected directly to the grid, making the rotor winding susceptible to high currents induced during grid faults. The rotor windings are connected to the grid via a back-to-back converter, which is very sensitive to over-currents and over-voltages. The crowbar system is activated during over-current on the rotor windings or/and over-voltage on the DC-link, allowing the wind turbine to stay connected to the grid during faults. An additional DC-chopper enables the injection of reactive power.