A doubly-fed induction generator, or DFIG, is an electric machine whose field windings and armature windings both connect separately to external equipment, letting it run at variable speed by feeding adjustable frequency AC power to its rotor windings while its stator connects directly to the electrical grid. Because the rotor frequency can differ freely from the grid frequency, a turbine fitted with a DFIG can speed up during a wind gust instead of being locked to a fixed grid speed, and only a fraction of the machine total power passes through the electronic converter, which keeps the converter smaller and cheaper than a fully rated one. The design traces back to the wound rotor induction motor Nikola Tesla patented in 1888, and later refinements, including Kramer and Scherbius drives and eventually modern IGBT based converters, steadily reduced the amount of heavy rotating equipment the technology needed. Doubly-fed induction generators are now widely used in wind turbines and in variable speed pumped storage hydropower plants.
Facts
Technology TypeA wound-rotor induction electric machine whose rotor and stator windings both connect separately to external equipment, letting the rotor run above or below synchronous speed for variable-speed generation 1 Invented YearThe doubly fed induction generator descends from the wound-rotor induction motor, with separate multiphase winding sets on rotor and stator, invented by Nikola Tesla in 1888; the slip-power-recovery drives (Kramer, then Scherbius) that define modern doubly fed operation followed in the early twentieth century, with no single later year documented for the generator concept itself. Classification
MaturityTRL 9: Actual System Proven in Operational Environment 1 Sources
1. Wikipedia: Doubly fed electric machine
WikipediaIntroduction, first paragraph
Doubly fed electrical generators are similar to AC electrical generators, but have additional features which allow them to run at speeds slightly above or below their natural synchronous speed.
History section, opening sentence
With its origins in wound rotor induction motors with multiphase winding sets on the rotor and stator, respectively, which were invented by Nikola Tesla in 1888, the rotor winding set of the doubly fed electric machine is connected to a selection of resistors via multiphase slip rings for starting.
Technology maturity, entity description (description property itself uncited on this atlas; cited against the entity's own live or freshly minted Wikipedia source instead)
Doubly-fed induction generators are now widely used in wind turbines and in variable speed pumped storage hydropower plants.
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