The document discusses a Doubly Fed Induction Generator (DFIG) which is used in wind turbines to generate electricity. A DFIG has both rotor and stator windings that are fed with three-phase AC signals. As the wind turbine spins the rotor of the DFIG, it induces a current in the rotor windings. The rotor's rotation also causes the stator's magnetic field to rotate, inducing a current in the stator windings. A variable frequency output from the DFIG is regulated using a machine side and grid side converter to provide a constant frequency output to the electric grid, regardless of changing wind speeds.

1. DULY FED INDUCTION
GENERATOR
PREPARED BY:-
SONU KUMAR BAIRWA

2. • A Doubly Fed Induction generator as its name
suggests is a 3 phase induction generator where
both the rotor and stator windings are fed with 3
phase AC signal.
• It consists of multi phase windings placed on
both the rotor and stator bodies. It also consists
of a multiphase slip ring assembly to transfer
power to the rotor.
• It is typically used to generate electricity in wind
turbine generators.

3. Double Fed Induction Generator
• The DFIG consists of a 3 phase wound rotor and a 3
phase wound stator. The rotor is fed with a 3 phase
AC signal which induces an ac current in the rotor
windings.
• As the wind turbines rotate, they exert mechanical
force on the rotor, causing it to rotate.
• As the rotor rotates the magnetic field produced due
to the ac current also rotates at a speed proportional
to the frequency of the ac signal applied to the rotor
windings.

4. • As a result a constantly rotating magnetic flux
passes through the stator windings which cause
induction of ac current in the stator winding.
Thus the speed of rotation of the stator magnetic
field depends on the rotor speed as well as the
frequency of the ac current fed to the rotor
windings.
• The basic requirement for the electricity
generation using wind energy is to produce ac
signal of constant frequency irrespective of the
wind speed. In other words the frequency of the
ac signal generated across the stator should be
constant irrespective of the rotor speed
variations.

5. • To achieve this, the frequency of ac signal
applied to the rotor windings need to be
adjusted.
A wind power generation system using double fed induction generator

6. • The frequency of the rotor ac signal increases as
the rotor speed decreases and is of positive
polarity and vice versa.
• Thus the frequency of rotor signal should be
adjusted such the stator signal frequency is
equal to the network line frequency.
• This is done by adjusting the phase sequence of
the rotor windings such that the rotor magnetic
field is in the same direction as the generator
rotor (in case of decreasing rotor speed) or in
opposite direction as the generator rotor (in case
of increasing rotor speed).

7. • The whole system consists of two back to back
converters – a machine side converter and a grid
side converter, connected in the feedback loop of the
system.
• The machine side converter is used to control the
active and reactive powers by controlling the d-q
components of the rotor and also torque and speed
of the machine.
• The grid side converter is used to maintain a
constant dc link voltage and ensures the unity power
factor operation by making the reactive power
drawn from the utility grid to zero.
• A capacitor is connected between the two converters
such that it acts as an energy storage unit.

8. • . This back to back arrangement provides a fixed
voltage fixed frequency output irrespective of the
variable frequency, variable voltage output of the
generator.
• Other applications of the induction generators
are fly-wheel energy storage systems, pumped
storage power plants, power converters feeding a
railway power grid from public grid where the
frequency is fixed.

9. SCHEME FOR WIND ENERGY
GENERATION BY USING DFIG
• A Wind Turbine: The wind turbine is typically a fan
consisting of 3 blades which rotate when wind strikes it.
The rotation axis should be aligned with the wind
direction.
• Gear Box: It is a high precision mechanical system
which uses a mechanical method to convert energy from
one device to another.

10. • Double Fed Induction Generator: It is an
electrical generator used to convert mechanical
energy to electrical energy which is in form of
variable frequency.
• Grid Side Converter: It is an AC-DC
converter circuit which is used to provide a
regulated DC voltage to the inverter. It is used
maintain a constant DC link voltage.
• Rotor Side Converter: It is a DC-AC inverter
which is used to provide controlled AC voltage to
the rotor.

11. REASON FOR USE OF DFIG IN WIND
GENERATION
• Constant frequency output signal to the grid
irrespective of the variable rotor speed.
• Low power rating required for the power electronic
devices and hence low cost of control system.
• Power factor is controlled, i.e. maintained at unity.
• Electric power generation at low wind speed.
• Power electronic converter has to handle the
fraction of the total load i.e.,20-30% and also cost of
this converter is low than in case of the other types
of generators.