2. Abstract
Introduction
Power electronics for fixed speed wind turbines
Power electronics for variable speed wind turbines
1)Partial scale power converter
2)Full scale power converter
Dynamic stability improvement with power electronics
Advantages and Disadvantages
Conclusion
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3. The global electrical energy consumption is rising and there is a steady increase of the
demand on the power capacity, efficient production, distribution and utilization of
energy. The traditional power systems are changing globally. Wind power is still the
most promising renewable Energy. The wind turbine system started with a few tens of
kilowatt power in the 1980s. Now, multi mega watt wind turbines are widely installed
even up to 6–8 MW. As the grid penetration and power level of the wind turbines
increase steadily, the wind power starts to have significant impacts to the power grid
system. Power electronic, the technology of efficiently processing electric power ,
plays an essential part in the integration of the dispersed generation units for good
efficiency and high performance of the power systems . Therefore, more advanced
generators, power electronic systems, and control solutions have to be introduced to
improve the characteristics of the wind power plant and make it more suitable to be
integrated into the power grid. Meanwhile, there are also some emerging technology
challenges, which need to be further clarified and investigated. This presentation
discusses the development trends in the technologies used for wind turbine systems.
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Introduction:
Need of power electronics:
Power Electronics is the study of electronic circuits used to convert and
control the flow of electrical power.
In the 1980s, the power electronics for wind turbines was just a soft
starter used to initially interconnect the squirrel-cage induction generator
with the power grid, and only simple thysistors were applied and they did
not carry the power continuously .
Since 2000, even more advanced back-to-back power converters were
introduced in large scale which started to regulate the generated power
from the wind turbines.
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Evolution of wind turbine size and the power electronics seen from
1980 to 2018 (estimated). Blue circle: the power coverage by power
electronics.
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Fixed speed wind turbines
Soft starter for fixed – speed wind turbines:
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The scheme consists of an SCIG, connected via a
transformer to the grid and operating at an almost fixed
speed.
The advantages of wind turbines with induction generators
are the simple and cheap construction, in addition that no
synchronization device is required.
These solutions are attractive due to cost and reliability.
8. Drawbacks:
The wind turbine has to operate at constant speed.
It requires a stiff power grid to enable stable operation and
It may require a more expensive mechanical construction
in order to absorb high mechanical stress, since wind
gusts may cause torque pulsations on the drive train.
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9. Variable speed wind turbine with
1) partial-scale power converter
2) Full scale power converter
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11. Doubly fed induction generator(DFIG) is adopted with
partial scale power converter for variable speed
controlled wind turbine.
This converter performs reactive power compensation
and smooth grid interconnection.
Slip rings and protection schemes are used in case of grid
faults
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Wind turbine system with full rated power
converter
13. The generator used for full rated power converter can be
synchronous/asynchronous generators.
Elimination of slip rings , full power , speed controllability are
the main advantages compared with DFIG concept.
There will be high power loss and switching loss in this
converter.
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14. The problem of the stability is often associated with different
types of faults in network such as
Tripping of transmission lines(over loads)
Loss of production capacity
short circuits
Short circuits of variety of forms
Fault ride through of induction generators
Fault ride through of DFIG with Crowbar
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15. Due to short circuits in the power systems the short circuit
current may result voltage drop in the wind generator terminal.
Due to voltage dip output electrical power and electromagnetic
torque of the wind turbine are reduced. Mechanical torque is
still applied on the wind turbine.
Turbine and generator are accelerated due to torque unbalance
. If the voltage is not able to recover back the generator speed
increases which increases the reactive power consumption.
The voltage may decrease further so the generator has to be
tripped out by the protection devices . Finally wind turbine is
disconnected and failed to ride-through the fault.
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16. To prevent the collapse of the power system the voltage has to
be recovered and speed has to be controlled.
Turbines equipped with pitching systems have the advantage
of pitching down the input mechanical torque which can limit
the acceleration of the generator.
When STATCOM is in operation the stability of the system
restores and system is at normal operation.
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17. High currents may damage the power electronic
converter connected with rotor winding of DFIG.
To avoid damages in power electronics the option
is to short circuit rotor winding by “Crowbar”.
Crowbar is connected between rotor of DFIG and
rotor-side converter.
It consists of diode bridge that rectifies the rotor
phase currents and a single thyristor in series with
a resistor Rcrow.
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High efficiency due to low loss in power semiconductor
devices.
High reliability of power electronic converter system.
Long life and less maintenance due to absence of any moving
parts.
Flexibility in operation
Fast dynamic response compared to electromechanical converter
system.
Small size and less weight, thus low installation cost.
High quality power to the grid.
Reduce the fluctuations in the power fed to grid.
Reduce acoustical noise from the wind turbines.
20. Circuits in power electronics system have a tendency to
generate harmonics in the supply system as well as the load
circuit.
AC to DC and AC to AC converter operate at low input power
factor under certain operating condition.
Regeneration of power is difficult in power electronic
converter system.
Power Electronic controllers have low overhead capacity
Expensive power electronic components required for full scale
power converter.
High power loss in the power converter.
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21. This presentation has reviewed the power electronic
application in wind turbine systems with different
generators and power electronic converters are
described. There is a continuing research for
improving the efficiency of these applications . For
higher reliability and lower energy cost power
electronics technology in WTS is developing.
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