Advanced Power Quality: Wind Turbines and DFIG

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ADVANCED POWER QUALITY
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Abstract
The use of wind energy in production of electrical power has become rampant in 21st C
due to it being cheap and very clean. This encourages exploitation of renewable energy to help
reduce the pressure which has been on the use of fossil fuels in the production of electrical
energy. This paper hence focuses on the use of wind turbines together with a special type of
generator know as DFIG (doubly fed Induction Generators). For a good quality of production of
electrical power computer software known as NEPLAN is adopted. This will hence make it
possible to model and check and the quality of the produced electrical energy.
Table of content
Contents
Table of content..........................................................................................................................................2

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Introduction.................................................................................................................................................2
Literature Review........................................................................................................................................3
MODELLING OVERVIEW...................................................................................................................7
DFIG proposed damping controller.........................................................................................................9
Types of wind turbines used for electricity production..........................................................................10
Adjustable speed turbines..................................................................................................................11
Constant speed turbines.....................................................................................................................11
Types of electric generators used for wind turbines...............................................................................12
Wind generation model of the MCC wind farm project.........................................................................13
Study of wind farm impact on power system.........................................................................................14
Project circuit diagram & explanation (DFIG Wind Turbine)...................................................................16
Components of circuit & explaining their parameters...............................................................................20
The result of running circuits.....................................................................................................................26
Conclusion.................................................................................................................................................34
Table of figure
Figure 1: Showing a crowbar system ..........................................................................................................6
Figure 2: Showing structure of General structure of DFIG wind turbine control.........................................8
Figure 3: Showing DFIG wind turbine framework ...................................................................................10
Figure 4: Showing RSC with the proposed PSS........................................................................................11
Figure 5: Showing Type C: variable speed with partial scale frequency converter turbine.......................15
Figure 6: Showing The Electric Power System of Albania and the wind farm connection........................17
Figure 7: Showing a circuit diagram for DFIG .........................................................................................18
Figure 8: Showing the circuit diagram of the DFIG obtained from NEPLAN...........................................20
Figure 9: Showing the Main components of the DFIG system..................................................................21
Figure 10: Showing Block diagram of the line side converter model........................................................22
Figure 11: Showing the Rotor crowbar connected.....................................................................................23
Figure 12: Showing DC link Chopper.......................................................................................................24
Figure 13: Showing a windmill gearbox....................................................................................................26
Figure 14: Showing a simplified block diagram for DFIG............................................................................26
Figure 15: Showing Main components of mechanical and electrical of type 1..........................................27
Figure 16: Showing System description WT1A........................................................................................28
Figure 17: Showing results by WT1A simulation......................................................................................28
Figure 18: Showing description of system type WT1B.............................................................................29
Figure 19: Showing results by WT1B simulation......................................................................................29
Figure 20: Showing mechanical and electrical components of type 2.......................................................30
Figure 21: Showing system description from NEPLAN software.............................................................30
Figure 22: Showing results by WT 2.........................................................................................................30

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Figure 23: Showing mechanical and electrical components of type 3 WT................................................31
Figure 24: Showing NEPLAN system description type 3A.......................................................................32
Figure 25: Showing NAPLAN results in graphical form for type 3A........................................................32
Figure 26: Showing NEPLAN system description for type 31A...............................................................33
Figure 27: Showing NAPLAN results in graphical form for type 31A......................................................33
Figure 28: Showing variation in active power generated in a given area...................................................34
Figure 29: Showing variation in reactive power generated in a given area................................................34
Figure 30: Showing the variation magnitude of the voltage produced.......................................................35
Introduction
The usage of wind has seriously increased for the last some years. From the Global Wind
Energy Council, the capacity of the wind power installed globally has for sure exceeded 318GW
this as by the year 2013 and it is anticipated to be about 712GW by the year 2020. As the
adoption of usage of the wind power increases into the systems some extra consideration of

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integrations are required and basically, the most important ones are for the power oscillation
damping, capability of voltage support during the disturbances of the network. All of these are in
direct connection of concern with the stability of the system. This is because poor damping of
electrical power oscillation and there is deficiencies of reactive power support can result in the
deterioration of stability of the system which in most cases results to power blackouts.
Nowadays the highly spread application of the wind turbine technology in the production
of electrical energy globally is what is known as DFIG (Doubly fed introduction generator). This
type of wind turbine power generation is asynchronously connected to the grid, therefore they
don ́t engage directly into power system electromechanically oscillation they don ́t produce new
oscillatory modes. The doubly-fed induction generator (DFIG) framework may be a prevalent
framework where the power electronic controls the rotor currents is interfaced to realize the
fluctuating speed essential for the greatest harvest of electrical energy in variable winds.
Since the power gadgets only handle the rotor power, ordinarily about 25 per cent of the
generally yielded power, the DFIG is advantageous due to their speed control with decreased
price and losses in electrical power. Framework model incorporates a physical illustration of the
edges, shaft and hub a continuous conversion which constitutes loss in thermal calculations, an
attractive demonstrate of the 3∅ transformers, grid and the transmission line. This DFIG is
basically employed in wind turbine during the generation of electrical energy because wind
speed can change abruptly. Therefore in this paper, we will analyze the use of DFIG in the wind
turbine in production of electrical energy, DFIG ensure a relatively smooth speed (which does
not change abruptly) for the wind turbine. And this needs a serious analysis in computer software
which will be done in one known as NEPLAN software for a better simulation as well as
analysis.

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Literature Review
DFIG is an electrical production principle broadly employed in the turbines of the wind.
Actually, it is grounded on generator (induction type) just as its name suggests. And it has a
wound rotor which is multiphase and also a slip ring which is also multiphase assembly with
brushes. Multiphase slip ring assembly can be avoided but this may result in some issues with
efficiency and cost during the operation. The basic principle of the DFIG is the windings of the
rotor which are joined to the grid through slip rings as well as an end to end converter source
which help in control of both rotor and the grid current. Therefore the effectiveness of the rotor
can differ freely from the frequency of the grid which is always 60 or50 Hz. It is very probable to
change the reactive and active power fed into the system from the stator separately of the
changing of the speed of the generator (Edrah, M, 2015).
This is possible by the usage of a converter to manage the rotor current. The means of
control employed here can be either vector control or direct torque control (DTC). Of the two
TDC is better than the Vector control in scenarios where more reactive current are needed from
the generation point. The DFIG rotors are basically wounded with 3 or 2 times the number of
stator’s turns. This hence means that the voltage of the rotor will be relatively higher while the
current will be lower. Thus in normal working ±30% range of speed operation in the speed
which is synchronous, the current rated of the converter is actually lower than results in lower
converter ́s cost. The limitation is that the confined working beyond the speed of operation is not
possible due to the higher rated voltage of the rotor.

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Moreover, the transient voltage due to the disturbances of the grid will as well be
magnified. To prevent high voltage rotor and higher current from such voltages from interfering
with the insulated gate bipolar transistors as well as diodes of converter ́s diodes the protection
which is known as crowbar is employed (Sorrentino, E., 2017). The diagram below illustrates the
crowbar system which can be employed here;
Figure 1: Showing a crowbar system (Sorrentino, E., 2017.
Basically, these crowbars can short circuit the windings of the rotor for less resistance if
there is the detection of excess currents and voltages. For it to be capable to continue with a
smooth run as speedily as it should an active crowbar must be employed. This active crowbar is
capable of removing the rotor ́s short in a fully managed manner. Therefore it is highly probable
to produce a reactive electrical current to the network through the dip of the voltage and for this;
it will aid the grid to recuperate from the fault. For very fewer voltages say 0 passes over, it is

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normal to delay till that time when the dip ends since it is otherwise is impossible for the phase
angle at the point where the reactive current need to be supplied.
A doubly-fed induction generator may be a wound-rotor doubly-fed electric generator
and has some preferences over ordinary induction generators in applications wind electrical
power. To begin with, when the circuit in the rotor is managed by a power gadgets converter, the
generator is capable of generating and transferring reactive power (Guo, J., 2017). This has
critical results for power framework steadiness and permits the generators to sustenance the
system during extreme disturbances due to voltage. Next, the control of the currents and voltages
of the rotor makes the generator to be in coordinated to the grid whereas the speed of the wind
turbine changes.
An adjustable wind turbine speed uses the present wind source more proficiently than a
stable wind turbine speed, particularly during conditions of small wind (Idrees, N.A.N., 2017).
Again, the converter cost is relatively less if it is equated to other adjustable speed arrangements
since only a part of the power (mechanical), ordinarily, 25–30%, is supplied to the network via
the converter. The General structure of a DFIG wind turbine can be illustrated using the diagram
below: