May 3, 2023 1

POWER ELECTRONICS TECHNOLOGY FOR WIND TURBINE SYSTEMS

Presented by

K.S.S.Pranavi

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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Objectives

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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ABSTRACT:

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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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Soft starter for fixed – speed wind turbines:

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.

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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Variable speed wind turbine with1) partial-scale power converter 2) Full scale power converter

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Power electronics for variable-speed wind turbines:

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wind turbine with partial-scale power converter

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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DFIG with partial scale power converter

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Wind turbine system with full rated power converter

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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Wind turbine system with full rated power converter

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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Dynamic stability improvement

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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Fault ride-through of induction generators

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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Fault ride-through of induction generators:

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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Fault ride-through of DFIG with Crowbar:

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Crowbar connected between the rotor of the DFIG and rotor-side converter

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Advantages :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 operationFast 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.

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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Disadvantages:

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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Conclusion :

Thank You