Patent ID: 8198742

Claim:
A variable speed wind turbine adapted to operate in a wind farm, said turbine being adapted to supply electrical power to an associated grid at a substantially fixed grid frequency during a low voltage condition, the turbine comprising a stator and a doubly-fed generator having a rotor adapted to turn at a rotor speed, the rotor and stator each comprising polyphase windings; the variable speed turbine comprising: a rotor inverter; a grid inverter; a rotor inverter controller for using scalar controls to control the rotor inverter to provide stator output power at a frequency substantially equal to a grid frequency and at unity power factor; a link for maintaining a substantially constant DC interface between the rotor inverter and the grid inverter; a grid inverter controller for using scalar controls to independently control individual grid inverter currents and provide output power at a frequency substantially equal to the grid frequency and at unity power factor; blade control means for maintaining a generator rotor speed at substantially the same speed before and during a low voltage condition; and protection means for the link and rotor for limiting damage to turbine components during a fault.