What is doubly-fed induction machines?
A doubly-fed induction machine (DFIM) is formed when the converter is present in the rotor circuit of WRIM and can be controlled by directing the power flow in to and out of the machine. Therefore, the DFIM can be operated either as a motor or as a generator both at sub and super synchronous speeds.
Why is it called doubly-fed induction generator?
Instead of the usual field winding fed with DC, and an armature winding where the generated electricity comes out, there are two three-phase windings, one stationary and one rotating, both separately connected to equipment outside the generator. Thus, the term doubly fed is used for this kind of machines.
Why is a doubly-fed induction generator Dfig used for wind power applications?
Traditional wind turbines have fixed turning speeds, while DFIG enables wind turbines to operate with various range of speeds. The back-to-back converter is connected to the rotor of the DFIG, and its purpose is to feed the rotor with currents of varying frequency, in order to reach the desired rotor speeds.
What rotor is used in Dfig?
1 Induction Generator Model. A seventh-order dynamic model [4] is used for the DFIG with rotor side converter. The model is derived from the voltage equations of an induction machine in a synchronous reference frame.
What is an advantage of using a double wound induction machine in a wind turbine?
Using a DFIG in wind turbines offers the same advantages as when a synchronous generator is used as a variable speed generator. Both types of schemes require two AC/DC converters. But, the two converters in DFIGs are much smaller than those in synchronous generators of similar output power.
What is the difference between induction generator and doubly-fed induction generator?
The difference between a regular asynchronous generator and a DFIG is that the prior is rotor excited whereas the latter is externally excited with an ac-dc-ac convertor. The 3 phase ac input current causes the flux field of the rotor to have an apparent rotation with respect to the rotor.
What is squirrel cage induction generator?
The squirrel cage induction generator (SCIG) is attached to the wind turbine by means of a gearbox. The SCIG stator windings are connected to a back to back full power converter. The gearbox provides speed and torque conversions from a rotating power source to another device, using gear ratios.
What is a doubly-fed motor?
Abstract—Doubly-fed electric machines are electric motors or electric generators where both the field magnet windings and armature windings are separately connected to equipment outside the machine. This is useful, for instance, for generators used in wind turbines.
Which wind turbine produces 100kw or greater?
Large wind turbines
Which type of wind turbines produce 100 kW or greater? Explanation: Large wind turbines are those of 100 kW rated capacity or greater. They are used to generate power for distribution in central power grids.
What is a doubly-fed induction machine?
As a summary, a doubly-fed induction machine is a wound-rotor doubly-fed electric machine and has several advantages over a conventional induction machine in wind power applications. First, as the rotor circuit is controlled by a power electronics converter, the induction generator is able to both import and export reactive power.
What is a double fed induction generator?
Double-fed induction generator. Double-fed induction generator (DFIG), a generating principle widely used in wind turbines. It is based on an induction generator with a multiphase wound rotor and a multiphase slip ring assembly with brushes for access to the rotor windings.
What is a doubly fed generator for wind turbines?
Doubly-fed generator for wind turbine. 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.
What is a brushless wound-rotor doubly-fed electric machine?
A better alternative is a brushless wound-rotor doubly-fed electric machine. The principle of the DFIG is that stator windings are connected to the grid and rotor winding are connected to the converter via slip rings and back-to-back voltage source converter that controls both the rotor and the grid currents.