電氣工程外文翻譯--風力發(fā)電對電力系統(tǒng)的影響

1、<p>　　外 文 翻 譯</p><p>　　題 目： 風力發(fā)電對電力系統(tǒng)的影響 </p><p>　　風力發(fā)電對電力系統(tǒng)的影響</p><p><b>　　簡奧斯丁，費力克斯</b></p><p>　?。娏ο到y(tǒng)及發(fā)電設(shè)備控制和仿真國家重點實驗室，紐約市曼哈頓區(qū)

2、）</p><p>　　摘要：風力發(fā)電依拖于氣象條件，并逐漸以大型風力發(fā)電場的形式并入電網(wǎng)，給電網(wǎng)帶來各種各樣的影響。電網(wǎng)并未專門設(shè)計用來接入風電，因此如果要保持現(xiàn)有的電力供應(yīng)標準，不能避免地需要進行一些相應(yīng)的調(diào)整。討論了在風力發(fā)電場并網(wǎng)時遇到的各種問題。由于風力發(fā)電具有大容量、動態(tài)和隨機的特性，它給電力系統(tǒng)的有功和無功潮流、電壓、系統(tǒng)穩(wěn)定性、電能質(zhì)量、短路容量、頻率和保護等方面帶來多種影響。針對這些問題提出了相

3、應(yīng)的解決建議和措施，以及更好地利用風力發(fā)電。</p><p>　　關(guān)鍵詞：風力發(fā)電；電力系統(tǒng)；影響；風電場</p><p><b>　　1.引言</b></p><p>　　人們普遍都能夠接受，可再生能源發(fā)電是未來電力供應(yīng)的必然趨勢。由于電力需求增長快速，對以化石燃料為基礎(chǔ)的發(fā)電是不可持續(xù)的。與之相反，風力發(fā)電作為一種有前途的可再生能源受到了很

4、多關(guān)注。當由于工業(yè)的發(fā)展和在世界大部分地區(qū)的經(jīng)濟增長而發(fā)電的消費需求一直穩(wěn)步增長時，它有減少污染排放和降低不可替代的燃料儲備消耗的潛力。</p><p>　　當大型風電場（幾百兆瓦）成為主流時，風力發(fā)電越來越受歡迎。2006年間，世界風能裝機容量從2005年的59091兆瓦達到74223兆瓦。在2006年極大的生長表明，決策者開始重視的風能發(fā)展能夠帶來的好處。由于到2020年12%的供電來于1250GW的安裝風力

5、發(fā)電機，將減少排放累積10771000000噸二氧化碳[1]。</p><p>　　大型風電場的電力系統(tǒng)具有很大的容量，動態(tài)隨機性，這將會挑戰(zhàn)電力系統(tǒng)的安全性和可靠性。而提供電力系統(tǒng)清潔能源的同時，風電場也會帶來一些對電力系統(tǒng)不利的因素。風力發(fā)電的擴展和風電在電力系統(tǒng)的比重增加，影響將很可能成為風力集成的技術(shù)性壁壘。因此，應(yīng)該探討其影響和提出克服這些問題的對策。</p><p>　　2.風

6、力發(fā)電發(fā)展現(xiàn)狀</p><p>　　從全球風能委員會（GWEC）的報告中，擁有最高裝機容量總數(shù)的國家是德國（20621兆瓦），西班牙（11615兆瓦），美國（11603兆瓦），印度（6270兆瓦）和丹麥（3136兆瓦）。世界范圍內(nèi)十三個國家現(xiàn)在可以算是達到1000兆瓦的風力發(fā)電能力，法國和加拿大在2006達到這一閾值。如圖1所示，直到2006年12月世界累計裝機容量前10名[2]。</p><

7、p>　　中國開始發(fā)展風電的時間很晚。只有在90年代它才走向市場化的發(fā)展道路和規(guī)模建設(shè)。這些年新增累積裝機容量如圖2顯示。單一機組容量從100千瓦到200千瓦，300千瓦600千瓦，750千瓦，1500千瓦逐步增加。</p><p>　　在2006年中國通過安裝風能的總?cè)萘窟_到1347兆瓦，增加了一倍以上的總?cè)萘?，比去年的?shù)值增長了70%。這給中國帶來多達2604兆瓦的電能，使中國成為世界第六大的市場。中國市

8、場在2006年大幅增長，這預(yù)計將繼續(xù)增長并加快增長。根據(jù)經(jīng)批準的和在建設(shè)中的項目，在2007年將安裝超過1500兆瓦。到2010年底在中國的風電目標為5000兆瓦[3]。</p><p>　　圖1 到2006年12月世界累計裝機容量</p><p>　　圖2 在中國累計和新增加安裝的風力發(fā)電能力</p><p>　　3.風力發(fā)電項目的特點</p>&l

9、t;p>　　從風能的角度來看，風能資源的最顯特點是其隨機不定性。風電場輸出的隨機變化主要源于風速的波動和方向。無論是地理性的和時間性的，風是很易變的。另外，無論是在空間和時間上，這種變化性持續(xù)的范圍非常廣泛。</p><p>　　由于時間和高度的影響，風速不斷變化。風變化的時間尺度顯示在圖3的風力頻譜圖上[4]。從一秒到一分鐘的范圍內(nèi)，陣風引起動蕩的高峰。每日的峰值取決于每天的風速變化而天氣高峰取決于天氣變

10、化，通常因每天或每周而異，但同時也包括季節(jié)性周期。</p><p>　　圖3風譜，布魯克海文國家實驗室工作</p><p>　　從電力系統(tǒng)的角度來看，湍流高峰可能會影響風力發(fā)電的電能質(zhì)量。然而，晝夜和天氣的高峰可能會影響電力系統(tǒng)的長期的平衡，在這樣的系統(tǒng)中風速預(yù)測起著非常顯著作用。</p><p>　　另一個重要問題是風能資源的長期變化。應(yīng)以加速到中心高度的風來計算

11、風電場的輸出。大量風速測量表明，風速在一年中大多數(shù)是柔和的，介于0和25米/秒的概率是相當大的；年均風速受制于威布爾分布[5]，如公式（1）。</p><p><b>　　(1)</b></p><p>　　其中：V是平均風速；k為形狀參數(shù)；c是尺度參數(shù)。</p><p>　　風力發(fā)電機的輸出之間的關(guān)系 和風速集線器V的高度可以近似表示為風力發(fā)

12、電機的輸出與風速或分段函數(shù)的曲線，如公式（2）。</p><p><b>　　(2)</b></p><p>　　其中： 是額定功率的風力發(fā)電機組的輸出；V是風速達樞</p><p>　　紐的高度VCI是停機風速；VCO被切出風速；VR被評為風速。</p><p>　　4．風力發(fā)電對電力系統(tǒng)的影響</p>

13、<p>　　在電力系統(tǒng)中風力發(fā)電面臨大型風電場對電網(wǎng)一體化的基本技術(shù)限制。風力發(fā)電對電力系統(tǒng)的影響包括有功和無功電流，電壓，系統(tǒng)穩(wěn)定性，電能質(zhì)量，短路容量和基礎(chǔ)設(shè)施的特點由于高容量的風力發(fā)電的動態(tài)和隨機性能。在技術(shù)上，它通過以下方式影響和必須詳細研究：</p><p>　?。?）有功和無功電流。</p><p>　　風力發(fā)電是一個間歇性和隨機的電源，將功率流復(fù)雜化。由于為了捕獲更

14、多的風能能源，許多風電場建成遠離負荷中心，總有傳輸風力發(fā)電一些的障礙。當引進額外的風力發(fā)電時一些傳輸或配電線路和其他電氣設(shè)備可能過載。因此，應(yīng)確?；ハ噙B接傳輸或配電線路不過載。有功和無功要求，都應(yīng)予以調(diào)查。無功功率應(yīng)不僅在PCC中產(chǎn)生，但也通過整個網(wǎng)絡(luò)產(chǎn)生，并應(yīng)本地補償[6]。</p><p>　　用于常規(guī)發(fā)電機的分析的方法是確定的，而忽略了不確定性的風速和負荷預(yù)測。因此，概率性的方法是比較適合風力發(fā)電的。約束以

15、概率形式描述，并且預(yù)期參數(shù)值，如電壓和功率，可以被計算。</p><p><b>　?。?）電壓調(diào)節(jié)</b></p><p>　　一旦風電場已經(jīng)確定了地點，連接到電網(wǎng)的點也必須確定。小型風力發(fā)電場，可以在低電壓下連接，從而節(jié)省了開關(guān)設(shè)備、電纜和變壓器的成本。如果擬議的發(fā)展規(guī)模太大導(dǎo)致不可以與當?shù)胤植茧娫催B接，進而不能滿足較高的電壓傳輸網(wǎng)絡(luò)的需要[7]。</p&g

16、t;<p>　　在電力系統(tǒng)中隨著風力發(fā)電安裝總?cè)萘康脑黾?，風力發(fā)電的變化會引起電壓變化，特別是如果并入電網(wǎng)，這可能不是專門設(shè)計用于迎合重要和可能快速變化的負載，這是由風力發(fā)電變化引起的。因此，需要采取監(jiān)管措施，使電壓保持在指定的范圍內(nèi)。然而為了控制電壓，可能導(dǎo)致增加對無功功率的輔助服務(wù)[8]。</p><p>　?。?）系統(tǒng)的穩(wěn)定性。</p><p>　　在風力發(fā)電的電力系統(tǒng)

17、中，電壓穩(wěn)定和頻率的穩(wěn)定性都受到風能功率集成影響，這不僅是因為風力發(fā)電的加入將改變流量分布，也因為風力發(fā)電機與傳統(tǒng)的同步機無論是在穩(wěn)態(tài)或暫態(tài)狀態(tài)時相比表現(xiàn)不大有同[9]。</p><p>　　對于目前的風力發(fā)電場，當發(fā)生干擾時，保護操作通常是切斷風電場與電網(wǎng)之間的連接。因此，在這種時侯的暫態(tài)穩(wěn)定性是非常重要的，尤其是與大型風電場的有機結(jié)合時最為重要。然而，由于電網(wǎng)結(jié)構(gòu)，風能也可能使電源集成系統(tǒng)的瞬態(tài)穩(wěn)定性變差。因

18、此，不同的電力系統(tǒng)，暫態(tài)穩(wěn)定性應(yīng)分別進行分析。</p><p>　　固定速度的風力渦輪機輸出有功功率時，它吸收無功功率。“風電場無功功率的整體需求是相當大，從而導(dǎo)致減少在PCC附近地區(qū)的電壓穩(wěn)定。與此相反，雙饋變速風力發(fā)電機組對無功功率有一定的控制能力。根據(jù)不同的操作和控制計劃，這種風力發(fā)電機組可以通過吸收或輸出無功功率控制電壓，有利于電壓的穩(wěn)定。電壓穩(wěn)定也與短路容量相關(guān)，傳輸?shù)腜CC行比R / X和在風力發(fā)電場

19、使用的無功補償方法有關(guān)。</p><p><b>　?。?）電能質(zhì)量。</b></p><p>　　風力發(fā)電的波動對相關(guān)電源（AC或DC）的傳輸、供電質(zhì)量有直接的影響。結(jié)果，大量的電壓波動，可能會導(dǎo)致電壓在調(diào)控范圍外變化，以及違反閃爍和其他電源的質(zhì)量標準。在連續(xù)的運行和開關(guān)操作，風力發(fā)電機組，引起電壓波動和閃爍，這些因素是風力發(fā)電影響電網(wǎng)電能質(zhì)量的主要因素。對于變速風

20、力渦輪機和恒定頻率轉(zhuǎn)換器造成的諧波問題，也應(yīng)考慮。</p><p>　　風力渦輪機對電網(wǎng)干擾有不同的原因，其中大多原因是風力機本體。有關(guān)參數(shù)列于表1[10]。平均發(fā)電量，湍流強度及風切變與氣象和地理條件因素相關(guān)。所有其他的原因不僅歸咎于電器元件的特點，如發(fā)電機，變壓器等。也是轉(zhuǎn)子和傳動系統(tǒng)的空氣動力學(xué)和機械性能的原因。渦輪形式（即變量與主要固定的速度檔位與節(jié)距調(diào)節(jié)）對風力渦輪機和風力發(fā)電場的電能質(zhì)量特性有重要性。

21、</p><p>　　表1.風力發(fā)電機和風力發(fā)電廠對電網(wǎng)造成的影響</p><p>　　電壓升高 電能生產(chǎn)</p><p><b>　　開關(guān)操作</b></p><p><b>　　塔影效應(yīng)</b></p>

22、;<p>　　電壓波動和閃爍 葉片調(diào)節(jié)誤差</p><p><b>　　偏航誤差</b></p><p><b>　　風切變</b></p><p><b>　　風速波動</b></p><p>　

23、　電壓峰值和谷值 開關(guān)操作</p><p>　　閃爍是由風力發(fā)電機組的有功功率或無功功率的的波動造成的。固定速度的風力發(fā)電機閃爍的主要原因是塔的尾流。而變速風力發(fā)電機，平滑了快速功率波動，塔的尾流不影響輸出功率。因此，變速風力發(fā)電機組的閃爍一般比定速閃爍風力發(fā)電機低。</p><p><b>　　（5）短路容

24、量。</b></p><p>　　往往大多數(shù)的風力發(fā)電場都遠離負荷中心建造，這意味著他們之間和其他間的電力系統(tǒng)的電氣之間的距離，是相當遠的。按照常理說，長電距離越長，使電壓變化越大，但短路問題越少[11]。</p><p>　　然而，風力發(fā)電場將能夠給未來的電力系統(tǒng)運行的短路電流計算帶來越來越重要的影響。原因是雙重的。一個是上述的事實，風力發(fā)電網(wǎng)站通常是遠離的傳統(tǒng)的電力中心。這

25、意味著短路電流的分布可能產(chǎn)生了很大的變化，導(dǎo)致一個完全不同的短路容量地圖。其他事實的原因是，今天，越來越多的風力發(fā)電，特別是以所謂的大型風力發(fā)電場（數(shù)百兆瓦）的形式。將風電場大量的個別單位連接在一起，總代能力將大大上升。</p><p>　　風電場對相鄰節(jié)點短路能力有很大影響，然而對遠離PCC節(jié)點的影響不大[9]。因此，當具有大容量的風電場并入電網(wǎng)時，相鄰變壓器和交換機的容量可能需要增加。應(yīng)該進一步研究的是如何判

26、斷風力發(fā)電對現(xiàn)有網(wǎng)絡(luò)上的電氣設(shè)備短路電流額定值的影響[12]。</p><p><b>　?。?）頻率調(diào)整。</b></p><p>　　為了在規(guī)定的標準范圍內(nèi)控制電力系統(tǒng)頻率，要求一些發(fā)電廠向電網(wǎng)公司提供頻率控制配套服務(wù)。然而，風力發(fā)電量總額的增加，其變化的頻率輸出是一個很重要的影響[8]。</p><p><b>　?。?）保護。

27、</b></p><p>　　電流在風電場和電網(wǎng)之間的流動是雙向的，這是在保護的設(shè)計和配置應(yīng)予以考慮的。無論風力發(fā)電機采用何種發(fā)電機，風電場的整合將增加電網(wǎng)故障水平，進而影響原有的電網(wǎng)保護裝置繼電器的設(shè)置。這可能需要增加新的保護裝置或修改原有保護設(shè)備的繼電器的設(shè)置。尤其是如果風電場連接到配電網(wǎng)絡(luò)，斷路器可能在風電場裝機容量增加時產(chǎn)生超負荷[8]。</p><p>　　5．減輕風

28、力發(fā)電的影響的對策</p><p>　　無功補償設(shè)備的應(yīng)用，如靜止無功補償（SVC）和靜止同步補償器（STATCOM）在風力發(fā)電中減輕其對電力系統(tǒng)的影響起著重要作用。為了保持電壓等級，電網(wǎng)公司可以提供額外的或升級的電壓控制設(shè)施。無功補償設(shè)備應(yīng)該安裝在風電場升壓變電站，這具有快速響應(yīng)特性，并且可不斷調(diào)節(jié)，如在SVC和STATCOM等。為了減少風力發(fā)電造成的電壓波動和閃爍，既需要速度控制應(yīng)加以改善，以便和俯仰角控制最

29、大限度地減少了風力發(fā)電機的輸出波動，而風力發(fā)電機的輸出最大化。同時，如在風場安裝輔助設(shè)備SVC和儲能裝置也可以減輕電壓波動和閃爍。在大多數(shù)情況下，快速作用無功補償設(shè)備，包括SVC和STATCOM，應(yīng)被納入為提高網(wǎng)絡(luò)的暫態(tài)穩(wěn)定的設(shè)備之中。</p><p>　　從風力發(fā)電方面，它可以通過不斷的功率因數(shù)控制或恒壓控制提高電力系統(tǒng)的電壓穩(wěn)定增加風力發(fā)電的滲透。從電網(wǎng)方面，這對加強和改變目前的網(wǎng)絡(luò)參數(shù)具有重要意義。以電壓源

30、換流器系統(tǒng)（VSC）為基礎(chǔ)的高壓直流輸電（VSC-HVDC系統(tǒng)）是一個不需要任何額外賠償?shù)膫鬏斚到y(tǒng)，因為這是轉(zhuǎn)換器的控制固有的[13]。因此，它將是一個很好的工具，它使風力發(fā)電成一個網(wǎng)絡(luò)，即使在一個弱網(wǎng)絡(luò)中，無需提高點短路比，也能實現(xiàn)。VSC-HVDC的有功功率控制能力，然后是一個完美的處理有源功率/頻率控制的工具。它有能力以一個很好的方式處理風電并足以快速反應(yīng)抵消電壓變化，它可以提高系統(tǒng)的穩(wěn)定性和電能質(zhì)量。</p>&l

31、t;p><b>　　6.結(jié)論</b></p><p>　　距今25年，風能已經(jīng)經(jīng)過很長的時間，它很可能會在未來20年繼續(xù)推進。有許多關(guān)于整合風力發(fā)電系統(tǒng)的運作和發(fā)展的問題。雖然風力發(fā)電取代了產(chǎn)生相當數(shù)量能量的傳統(tǒng)植物，關(guān)注點都集中在了風力發(fā)電和電網(wǎng)之間的相互作用上。本文提供了一個概覽風力發(fā)電對電力系統(tǒng)的影響和相應(yīng)的對策建議來處理這些問題，為了適應(yīng)風在電力系統(tǒng)的發(fā)電。</p>

32、<p><b>　　參考文獻</b></p><p>　　[1] EWEA．Wind force 12[EB/OL]．</p><p>　　[2] GWEC．Global wind energy markets continue to boom-2006 another record year[EB/OL]．</p><p>　　

33、[3] Liu Yan，Wang Wei wind power information Technology，2007</p><p>　　[4] Burton T，Sharpe D，Jenkins N，et al．Wind energy handbook[M]．Chichester：John Wiley & Sons Ltd，2001</p><p>　　[5] Bowden G

34、 J，Barker P R，Shestopal V O，et al．Weibull distribution function[J]．Wind Engineering，1983，7(2)：85-98</p><p>　　[6] Fan Zhenyu，Enslin J H R．Challenges, principles and issues relating to the development of wind

35、power in China[C]．IEEE PES PSCE，2006：748-754</p><p>　　[7] O'Gorman R，Redfern M A．The difficulties of connecting renewable generation into utility networks[C]．IEEE Power Engineering Society General Meetin

36、g，2003，3：1466-1471</p><p>　　[8] Wang Wei sheng，Chen Mozi．Towards the integrating wind power into power grid in China[J]．Electricity，2004，(4)：49-53</p><p>　　[9] Chi Yong ning，Liu Yan hua，Wang Wei

37、 sheng，et al．Study on impact of wind power integration on power system[J]．Power System Technology，2007，31(3)：77-81</p><p>　　[10] Ackermann T．Wind power in power systems[M]．Chichester：John Wiley & Sons Lt

38、d，2005</p><p>　　[11] Kumano T．A short circuit study of a wind farm considering mechanical torque fluctuation[C]．IEEE Power Engineering Society General Meeting，2006：1-6</p><p>　　[12] Strbac G，Sha

39、koor A，Black M，et al．Impact of wind generation on the operation and development of the UK electricity systems[J]．Electric Power Systems Research，2007，77(9)：1214-1227</p><p>　　[13] Eriksson K，Liljegren C，Sobr

40、ink K．HVDC light experience sapplicable for power transmission from offshore wind power parks[EB/OL]．</p><p><b>　　外文原文</b></p><p>　　Influence Research of Wind Power Generation on Pow

41、er Systems</p><p>　　Jane Austen，Kurt Felix</p><p>　?。⊿tate Key Lab of Control and Simulation of Power Systems and Generation Equipments，Manhattan District，New York，United States）</p><

42、p>　　Abstract: Wind power generation is always weather dependent and has the trend of being integrated to power systems as the form of large-scale wind farms, which influences on power systems. Since the power network

43、was not designed specifically to accommodate this type of generation, there are inevitably some points at which modifications must be executed if existing standards of electricity supply are to be maintained. This paper

44、discusses in general terms the problems which are encountered by th</p><p>　　Key Words: wind power generation；power system；influence；wind farms</p><p>　　0．Introduction</p><p>　　Ther

45、e is widespread acceptance that renewable generation is the future of electricity supply. Generation based on fossil fuels is not sustainable as power electricity is being consumed rapidly. On the contrary, wind power ha

46、s attracted much attention as a promising renewable energy resource. It has potential benefits in curbing emissions and reducing the consumption of irreplaceable fuel reserves when the demand for power electricity has be

47、en steadily growing due to the industrial developments a</p><p>　　Wind power generation is becoming more and more popular while the large-scale wind farm(hundreds of megawatts) is the mainstream one. During

48、2006, the world’s installed wind capacity reached 74 223 MW, up from 59 091 MW in 2005,which include wind energy developments in more than 70 countries around the world. The tremendous growth in 2006 shows that decision

49、makers are starting to take seriously the benefits that wind energy development can bring.</p><p>　　There are no technical, economic or resource barriers to supplying 12% of the world’s electricity needs wit

50、h wind power alone by 2020, and this against the challenging backdrop of a projected two thirds increase of electricity demand by that date. The report is a crucial tool in the race to cut greenhouse gas emissions as 12%

51、 electricity from a total of 1 250 GW of wind power installed by 2020 will save a cumulative 10771 million tons of CO2[1].</p><p>　　Large-scale wind farms connected to power systems have characteristics of h

52、igh capacity, dynamic and stochastic performance, which challenges system security and reliability. While providing the clean power for power systems, wind farms will also bring about some unfavorable influence on power

53、systems. With the expansion of wind power generation and the increase of wind power ratio in a power system, the influence will likely become the technical barriers for wind power integration. Therefore, t</p><

54、;p>　　According to the issues mentioned above, this paper discusses in general terms the problems which are encountered by the developers of wind power generation projects and by utility grids when dealing with project

55、s to integrate wind farms to power systems. Due to the characteristics of high-capacity, dynamic and stochastic performance of wind power generation, the influence includes active and reactive power flow, voltage, system

56、 stability, power quality, short-circuit capacity, system reserve, f</p><p>　　1．Development situation of wind power generation</p><p>　　From the report of the Global Wind Energy Council (GWEC),

57、the countries with the highest total installed capacity are Germany (20 621 MW), Spain (11 615MW), the USA (11603MW), India(6270 MW) and Denmark (3 136 MW). Thirteen countries around the world can now be counted among th

58、ose with over 1000 MW of wind capacity, with France and Canada reaching this threshold in 2006. Fig.1 shows the top 10 cumulative installed capacity of the world until December, 2006[2].</p><p>　　China start

59、ed to develop wind power very late. It stepped into the stage of commercialized development and scale construction only in 1990s. Accumulated and newly added installed generating capacity over the years is shown in Fig.2

60、.The single-unit capacity increased from 100 kW, 200 kW, and 300 kW to 600 kW, 750 kW, and 1500 kW step by step.</p><p>　　Fig. 1 Top 10 cumulative installed capacity of the world until December,2006</p>

61、;<p>　　Fig. 2 Accumulative and newly-added installed capacity of wind power in China</p><p>　　China doubled more than its total installed capacity by installing 1 347 MW of wind energy in 2006, a 70%

62、increase from last year’s figure. This brings China up to 2 604 MW of capacity, making it the sixth largest market world wide. the Chinese market has grown substantially in 2006, and this growth is expected to continue a

63、nd speed up. According to the list of approved projects and those under construction, more than 1 500 MW will be installed in 2007. The goal for wind power in China by the en</p><p>　　2．Characteristics of wi

64、nd power generation</p><p>　　From the point of view of wind energy, the most striking characteristic of the wind resource is its variability. The stochastic variation of wind farms outputs root mainly in flu

65、ctuation of the wind speeds and directions. The wind is highly variable, both geographically and temporally. Furthermore this variability persists over a very wide range of scales, both in space and time.</p><

66、p>　　The wind speed varies continuously as a function of time and height. The time scales of wind variations are presented in Fig.3 as a wind frequency spectrum[4]. The turbulent peak is caused by gusts in the sub seco

67、nd to minute range. The diurnal peak depends on daily wind speed variations and the synoptic peak depends on changing weather patterns, which typically vary daily to weekly but include also seasonal cycles.</p>&l

68、t;p>　　Fig. 3 Wind spectrum farm Brookhaven based on work by van der Hoven</p><p>　　From a power system perspective, the turbulent peak may affect the power quality of wind power generation. The influence

69、of turbulences on power quality depends very much on the turbine technology applied. Variable-speed wind turbines, for instance, may absorb short-term power variations by the immediate storage of energy in the rotating m

70、asses of wind turbine drive trains. That means that the power output is smoother than strongly grid-coupled turbines, fixed-speed wind turbines. Diurnal and sy</p><p>　　Another important issue is the long-te

71、rm variations of the wind resources. The wind speed up to the height of the hub should be known to calculate the wind farm output. A number of measurements of wind speeds show that wind speeds are mostly mild in a year;

72、their probabilities between 0 and 25m/s are considerable; most of the average annual wind speeds subject to the Wei bull distribution[5], as in formula(1).</p><p><b>　　(1)</b></p><p>

73、;　　where: v is average wind speed; k is shape parameter; c is scale parameter.</p><p>　　The relationship between the wind turbine output Pw and the wind speed up to the height of the hub v can be expressed a

74、pproximately as the curve of wind turbine’s outputs vs. wind speed or a subsection function, as in formula (2).</p><p><b>　　(2)</b></p><p>　　where: Pw is rated output of the wind tur

75、bine; v is wind speed up to the height of the hub; VCI is cut-in wind speed; VCO is cut-out wind speed; VR is rated wind speed.</p><p>　　3．Influence of wind power generation on power systems</p><p

76、>　　High penetration of wind power in the power systems faces fundamental technical limits with regard to the integration of large-scale wind farms to the grid. The influence of wind power generation on power systems i

77、ncludes active and reactive power flow, voltage, system stability, power quality, short-circuit capacity, system reserve and infrastructure due to the characteristics of high-capacity, dynamic and stochastic performance

78、of wind power generation. Technically, it influences the gird in t</p><p>　?。?）Active and Reactive Power Flow.</p><p>　　Wind power is a kind of intermittent and stochastic power source, which wi

79、ll complicate the power flow. Because many wind farms are built far away from load centers in order to capture more wind energy, there is always some obstacle of transmitting wind power. Some transmission or distribution

80、 lines and other electrical equipments may be over-loaded when the additional wind power generation is introduced. So it should be ensured that the interconnecting transmission or distribution lines will no</p>&l

81、t;p>　　The methods utilized for analysis of conventional generators are certain and ignore the uncertainty of wind speed and load forecasts. Therefore, the probabilistic method is more suitable for wind power generatio

82、n. This model is based on the wind speed distribution, such as formula (1). The constraints are described by probabilistic forms and the expected values of parameters, such as voltages and powers can be computed.</p&g

83、t;<p>　?。?）Voltage Regulation.</p><p>　　Once a wind farm has identified its site, the point at which connection to the grid must be identified. Small wind farm can connect at lower voltage, thereby sa

84、ving on switchgear, cable and transformer costs. If the size of the proposed development is too large to be connected at the local distribution voltage, access to the transmission network at a higher voltage is required[

85、7].</p><p>　　After failures, if the transient unstability does not occur in power systems, some wind turbines shut down due to their low voltage protections. Then outputs of wind farms decrease, which means

86、that the power system lose reactive loads. Therefore the voltage levels climb up, even beyond the upper limits of wind farms buses.</p><p>　　Capacitors are the common reactive power compensation methods. Whe

87、n voltage levels dropdown, the amount of compensation decreases much. However the reactive power demands increase when the asynchronous machines are utilized in wind farms. So voltage levels drop down more, even beyond t

88、he lower limits of wind farms buses.</p><p>　　With the increase of wind power installed capacity in power systems, the variability of wind power generation causes variability of voltage level, particularly i

89、f integrated into the grid which might not be specifically designed to cater for the significant and possibly rapid load variations (compared with normal customer load variation) caused by highly variable wind power gene

90、ration. Therefore, the regulatory measures are needed to maintain the voltage level in a specified range. However, the </p><p>　?。?）System Stability.</p><p>　　In the power system with high wind

91、power penetration, the transient stability, voltage stability and frequency stability are all influenced by the wind power integration not only because the injection of wind power will change the power flow distribution,

92、 transferred power of each transmission line and total inertia of the whole power system, but also because the wind turbine generators perform differently in either steady-state or transient-state compared with the conve

93、ntional synchronous machi</p><p>　　For current operation of wind farms, protections usually cut off the connections between wind farms and the grid when great disturbances occur. This is equivalent to arouse

94、 new generators tripping disturbance after the great disturbances. So the transient stability in such moment is very crucial, especially when large-scale wind farms are integrated. Compared the variable-speed wind turbin

95、e based on the doubly-fed induction generator (DFIG) with the fixed-speed wind turbine based on the inductio</p><p>　　The fixed-speed wind turbine absorbs the reactive power when outputting the active power.

96、 The whole demand of a wind farm for the reactive power is considerable, which lead to the decrease of the voltage stability in the area near PCC. On the contrary, the variable-speed wind turbine based on DFIG has certai

97、n ability to control the reactive power. According to different operation and control schemes, this wind turbine can absorb or output the reactive power to control the voltage, which benefits</p><p>　?。?）Pow

98、er Quality.</p><p>　　Fluctuations in the wind power and the associated power transport (AC or DC), have direct consequences to the power supply quality. As a result, large voltage fluctuations may result in

99、voltage variations outside the regulation limits, as well as violations on flicker and other power quality standards. During the continuous operation and switching operation, wind turbine causes voltage fluctuation and f

100、licker, which are main concerns of unfavorable influence of wind power generation on power qua</p><p>　　The grid interferences of wind turbines or wind farms have different causes, which are mostly turbine-s

101、pecific. The relevant parameters are listed in Tab.1[10]. Average power production, turbulence intensity and wind shear refer to causes that are determined by meteorological and geographical conditions. All the other cau