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چكيده انگليسي :

Contribution of DFIG Based Wind Turbines in Power System Frequency Improvement Mohammad Akbari Kelishadi Mohamad ak@gmail com 03 05 2010 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Seyed Mohammad Madani madani104@yahoo comAbstract Nowadays renewable energies play an important role in electrical power generation Between different kindsof renewable resources wind energy has had the fastest growth Wind farms affect power systems indifferent manner of conventional synchronous generators It is because of their different characteristics anddynamic behavior On the other hand by increasing the wind farms capacity new grid codes ask them tosupport power system by providing some ancillary services like voltage and frequency control In this thesis DFIG based wind turbines as one of the most commonly used wind turbine structures arestudied and their impact on power system frequency deviation is evaluated It is proved that their outputactive power varies a little after occurrence of active power imbalance in the grid In the other word theydon t contribute in frequency control of power system So if conventional synchronous plants are displacedby wind farms system frequency excursion will increase On the other hand DFIG based wind turbines havesome features make them potentially capable to participate in frequency control To use these capabilitieseffectively some modifications in the DFIG control system are necessary Methods make DFIGs capable toparticipate in grid frequency control are divided into two main groups The first one is those results in DFIGcontribution just in short term frequency control for few seconds and the other one is methods make DFIGscapable to provide primary frequency control service for power system In the short term methods asupplementary loop is added to active or voltage control loops The aim of supplementary loop in the activepower control loop is to increases DFIG output active power immediately after occurrence of active powerimbalance in the grid The source of this additional active power is kinetic energy stored in wind turbineinertia The method based on modifying of voltage control loop tries to manage demand side by controllingof bus voltages In this way DFIG reduces its bus voltage to reduce the DFIG capability in fast control ofreactive power is used and bus voltages are controlled and grid load consequently These methods usually usefrequency deviation f or rate of change of frequency df dt as a criterion of active power imbalanceintensity The impact of using each of these indexes in improving frequency deviations is analyzed Forcontribution of wind farms in primary frequency control they should be equipped with some amount ofspinning reserve power Providing reserve power by a wind farm is different with conventional generationplants because in a wind farm wind speed determines the available power So reserve power is changedaccording to wind condition The reserve power is provided by extracting just a part of available wind powerand not all of it as it is done in maximum power point tracking mode In this way wind farm can increase itsoutput power for a long period of time In this thesis methods for providing reserve power for wind farms indifferent wind speed ranges are introduced Finally a new algorithm is proposed that improves participation of DFIG based wind turbines in short termfrequency control The method uses average frequency concept to estimate the amount of active powerimbalance in power system immediately after its occurrence and then compensate it by wind farm Keywords Frequency control Wind farm Doubly fed induction generators Frequency deviation index Rate ofchang of frequency index

اكبري كليشادي، محمد

مشاركت توربين هاي بادي القايي دو تحريكه در بهبود كنترل فركانس شبكه

كنترل كوتاه مدت فركانس , نيروگاه بادي , شاخص افت فركانس , شاخص نرخ تغييرات