It is also named as Double Fed Induction Generator (DFIG)
In the past few
decades wind power has become one of the most attractive solutions for clean
and renewable energy. Recent years have seen a huge application and improvement
of wind energy systems particularly with the improvement in power semiconductor
technology, high speed DSP controllers and software tools which facilitate rapid
implementation of digital control algorithms and real-time control. Now-a-days
most of the renewable energy generation is done through variable speed
induction generators. Squirrel cage
and Wound rotor induction machines as well as synchronous machines have found
increasing application in the wind energy. Though the requirements of utility
(grid/load) are not fulfilled directly just by the machine, the control
strategy is used in both the stator as well as rotor side along with power
electronic converters to fulfil the requirements of utility.
The statistical
data conveys that Double Output Induction Generator (DOIG) based wind turbine
with variable speed and variable pitch control is the most common wind turbine
in the growing wind market. The basic control of the total system (DOIG with
Two back-to-back connected
PWM voltage-fed converters) is that the
machine-side converter controls the active and reactive power by controlling
the dq components of rotor current
(i.e.,
and
), while the
grid-side converter controls the dc-link voltage.
The double
output induction generator (DOIG) can supply power at constant voltage and
constant frequency while the rotor speed varies and so supplying grid connected
or isolated load. This makes it suitable for variable speed wind energy
applications. The
load voltage is maintained at constant frequency and its magnitude is regulated
through control of the stator flux of the generator. By means of a bidirectional converter the speed
range can be extended above and below synchronous speed and power can be
generated both from the stator and the rotor. The main advantage of this type
of DOIG drive is that the rotor converter need only be rated for a fraction of
the total output power, the fraction depending on the allowable sub- and
super-synchronous speed range.
