風(fēng)電對(duì)電網(wǎng)影響-中英文對(duì)照翻譯

1、<p>　　畢業(yè)設(shè)計(jì)(論文)外文資料翻譯</p><p>　　學(xué) 院： </p><p>　　專 業(yè)： </p><p>　　姓 名： </p>

2、<p>　　學(xué) 號(hào)： </p><p>　　外文出處： Power System Technology. 2007. </p><p>　　31(20) </p><p>　　附 件： 1.外文資料翻譯譯文；2.外文原文。 </p&

3、gt;<p>　　附件1：外文資料翻譯譯文</p><p>　　風(fēng)力發(fā)電對(duì)電力系統(tǒng)的影響</p><p><b>　　簡奧斯丁，費(fèi)力克斯</b></p><p>　　（電力系統(tǒng)及發(fā)電設(shè)備控制和仿真國家重點(diǎn)實(shí)驗(yàn)室，紐約市曼哈頓區(qū)）</p><p>　　摘要：風(fēng)力發(fā)電依賴于氣象條件，并逐漸以大型風(fēng)電場的形式并入

4、電網(wǎng)，給電網(wǎng)帶來各種影響。電網(wǎng)并未專門設(shè)計(jì)用來接入風(fēng)電，因此如果要保持現(xiàn)有的電力供應(yīng)標(biāo)準(zhǔn)，不可避免地需要進(jìn)行一些相應(yīng)的調(diào)整。討論了在風(fēng)電場并網(wǎng)時(shí)遇到的各種問題。由于風(fēng)力發(fā)電具有大容量、動(dòng)態(tài)和隨機(jī)的特性，它給電力系統(tǒng)的有功/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(hù)等方面帶來影響。針對(duì)這些問題提出了相應(yīng)的解決建議和措施，以及更好利用風(fēng)力發(fā)電。</p><p>　　關(guān)鍵詞：風(fēng)力發(fā)電；電力系統(tǒng)；影響；風(fēng)

5、電場</p><p><b>　　0、引言</b></p><p>　　人們普遍接受，可再生能源發(fā)電是未來電力的供應(yīng)。由于電力需求快速增長，對(duì)以化石燃料為基礎(chǔ)的發(fā)電是不可持續(xù)的。正相反，風(fēng)力發(fā)電作為一種有前途的可再生能源受到了很多關(guān)注。當(dāng)由于工業(yè)的發(fā)展和在世界大部分地區(qū)的經(jīng)濟(jì)增長而發(fā)電的消費(fèi)需求一直穩(wěn)步增長時(shí)，它有減少排放和降低不可替代的燃料儲(chǔ)備消耗的潛力。</

6、p><p>　　當(dāng)大型風(fēng)電場（幾百兆瓦）是一個(gè)主流時(shí)，風(fēng)力發(fā)電越來越更受歡迎。2006年間，世界風(fēng)能裝機(jī)容量從2005年的59091兆瓦達(dá)到74223兆瓦。在2006年極大的生長表明，決策者開始重視的風(fēng)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(fēng)電裝機(jī)，將節(jié)約累積10771000000噸二氧化碳[1]。</p><p>　　大型風(fēng)電場的電力系統(tǒng)具有很高的容量，動(dòng)態(tài)

7、隨機(jī)性能，這將會(huì)挑戰(zhàn)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(shí)，風(fēng)農(nóng)場也會(huì)帶來一些對(duì)電力系統(tǒng)不利的因素。風(fēng)力發(fā)電的擴(kuò)展和風(fēng)電在電力系統(tǒng)的比重增加，影響將很可能成為風(fēng)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(duì)策。</p><p>　　1、風(fēng)力發(fā)電發(fā)展現(xiàn)狀</p><p>　　從全球風(fēng)能委員會(huì)（GWEC）的報(bào)告中，擁有最高裝機(jī)容量總數(shù)的國家是德國（20621兆瓦），

8、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(gè)國家現(xiàn)在可以算是達(dá)到1000兆瓦的風(fēng)力發(fā)電能力，法國和加拿大在2006達(dá)到這一閾值。如圖1所示，直到2006年12月世界累計(jì)裝機(jī)容量前10名[2]。</p><p>　　中國開始發(fā)展風(fēng)電很晚。只有在90年代它才走向市場化的發(fā)展和規(guī)模建設(shè)。這些年新增累積裝機(jī)容量如圖2顯示。單一機(jī)組容量從100千瓦，200千

9、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(fēng)能的1347兆瓦，增加了一倍以上的總量容量，比去年的數(shù)值增長了70%。這給中國帶來多達(dá)2604兆瓦的能力，使中國成為世界第六個(gè)最大的市場。中國市場在2006年大幅增長，這預(yù)計(jì)將繼續(xù)增長并加快增長。根據(jù)經(jīng)批準(zhǔn)的和在建設(shè)中的項(xiàng)目，在2007年將安裝超過1500兆瓦。到2010年底在中國的風(fēng)電目標(biāo)為5000兆瓦[

10、3]。</p><p>　　圖1 到2006年12月世界累計(jì)裝機(jī)容量</p><p>　　圖2 在中國累計(jì)和新增加安裝的風(fēng)力發(fā)電能力</p><p>　　2、風(fēng)力發(fā)電項(xiàng)目的特點(diǎn)</p><p>　　從風(fēng)能的角度來看，風(fēng)能資源的最顯特點(diǎn)是其變化性。風(fēng)電場輸出的隨機(jī)變化主要根源于風(fēng)速的波動(dòng)和方向。無論是地理性和時(shí)間性，風(fēng)是很易變的。此外，無論是在

11、空間和時(shí)間上，這種變化性持續(xù)的范圍非常廣泛。</p><p>　　由于時(shí)間和高度的功能，風(fēng)速不斷變化。風(fēng)變化的時(shí)間尺度顯示在圖3的風(fēng)力頻譜圖上[4]。在一秒到分鐘的范圍陣風(fēng)引起動(dòng)蕩的高峰。每日的峰值取決于每天的風(fēng)速變化和天氣高峰取決于天氣變化，通常因每天或每周而異，但也包括季節(jié)性周期。</p><p>　　Fig. 3 Wind spectrum farm Brookhaven based

12、 on work by van der Hoven</p><p>　　從電力系統(tǒng)的角度來看，湍流高峰可能會(huì)影響風(fēng)力發(fā)電的電能質(zhì)量。然而，晝夜和天氣的高峰，可能會(huì)影響長期的電力系統(tǒng)的平衡，在這樣的系統(tǒng)中風(fēng)速預(yù)測起著顯著作用。</p><p>　　另一個(gè)重要問題是風(fēng)能資源的長期變化。應(yīng)知道加速到中心高度的風(fēng)來計(jì)算風(fēng)電場的輸出。大量風(fēng)速測量表明，風(fēng)速在一年中大多數(shù)是柔和的，介于0和25米/秒的

13、概率是相當(dāng)大的；年均風(fēng)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(fēng)速；k為形狀參數(shù)；c是尺度參數(shù)。</p><p>　　風(fēng)力發(fā)電機(jī)的輸出之間的關(guān)系PW和風(fēng)速集線器V的高度可以近似表示為風(fēng)力發(fā)電機(jī)的輸出與風(fēng)速或分段函數(shù)的曲線，如公式（2）。</p><

14、;p><b>　　(2)</b></p><p>　　其中：PW是額定功率的風(fēng)力發(fā)電機(jī)組的輸出；V是風(fēng)速達(dá)樞紐的高度VCI是停機(jī)風(fēng)速；VCO被切出風(fēng)速；VR被評(píng)為風(fēng)速。</p><p>　　3、風(fēng)力發(fā)電對(duì)電力系統(tǒng)的影響</p><p>　　在電力系統(tǒng)中風(fēng)力發(fā)電面臨大型風(fēng)電場對(duì)電網(wǎng)一體化的基本技術(shù)限制。風(fēng)力發(fā)電對(duì)電力系統(tǒng)的影響包括有效功和無

15、效功流，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(diǎn)由于高容量的風(fēng)力發(fā)電的動(dòng)態(tài)和隨機(jī)性能。在技術(shù)上，它通過以下方式影響和必須詳細(xì)研究：</p><p>　?。?）有功和無功流。</p><p>　　風(fēng)力發(fā)電是一個(gè)間歇性和隨機(jī)的電源，將功率流復(fù)雜化。由于為了捕獲更多的風(fēng)能能源，許多風(fēng)電場建成遠(yuǎn)離負(fù)荷中心，總有傳輸風(fēng)力發(fā)電一些的障礙。當(dāng)引進(jìn)額外的風(fēng)力發(fā)電時(shí)一些傳輸或配電線路和其他電氣設(shè)

16、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(gè)網(wǎng)絡(luò)產(chǎn)生，并應(yīng)本地補(bǔ)償[6]。</p><p>　　用于常規(guī)發(fā)電機(jī)的分析的方法是確定的，而忽略了不確定性的風(fēng)速和負(fù)荷預(yù)測。因此，概率性的方法是比較適合風(fēng)力發(fā)電的。約束以概率形式描述，并且預(yù)期參數(shù)值，如電壓和功率，可以被計(jì)算。</p><p><b>　?。?/p>

17、2）電壓調(diào)節(jié)</b></p><p>　　一旦風(fēng)電場已經(jīng)確定了其地點(diǎn)，連接到電網(wǎng)的點(diǎn)必須確定。小型風(fēng)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(dāng)?shù)胤植茧妷旱倪B接，進(jìn)而不能滿足較高的電壓傳輸網(wǎng)絡(luò)的需要[7]。</p><p>　　在電力系統(tǒng)中隨著風(fēng)力發(fā)電安裝容量的增加，風(fēng)力發(fā)電的變化引起電壓變化，特別是如果并入電網(wǎng)，這

18、可能不是專門設(shè)計(jì)用于迎合重要和可能快速變化的負(fù)載，這是由風(fēng)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，這可能導(dǎo)致增加對(duì)無功功率的輔助服務(wù)[8]。</p><p>　　（3）系統(tǒng)的穩(wěn)定性。</p><p>　　在風(fēng)力發(fā)電的電力系統(tǒng)中，電壓穩(wěn)定和頻率的穩(wěn)定性都受到風(fēng)功率集成影響，這不僅是因?yàn)轱L(fēng)力發(fā)電的加入將改變流量分布，也因?yàn)轱L(fēng)力發(fā)電機(jī)與傳統(tǒng)的同步機(jī)

19、無論是在穩(wěn)態(tài)或瞬態(tài)狀態(tài)時(shí)相比表現(xiàn)不同[9]。</p><p>　　對(duì)于目前的風(fēng)力發(fā)電場，當(dāng)發(fā)生干擾時(shí)，保護(hù)操作通常是切斷風(fēng)電場之間的連接電網(wǎng)。因此，在這種時(shí)刻的暫態(tài)穩(wěn)定是非常重要的，尤其是當(dāng)大型風(fēng)電場的有機(jī)結(jié)合時(shí)最為重要。然而，由于電網(wǎng)結(jié)構(gòu)，風(fēng)也可能使電源集成系統(tǒng)的瞬態(tài)穩(wěn)定性差。因此，不同的電力系統(tǒng)，暫態(tài)穩(wěn)定性應(yīng)分別進(jìn)行分析。</p><p>　　固定速度的風(fēng)力渦輪機(jī)輸出有功功率時(shí)，它吸收

20、無功功率。“風(fēng)電場無功功率的整體需求是相當(dāng)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?zhàn)兯亠L(fēng)力發(fā)電機(jī)組對(duì)無功功率有一定的控制能力。根據(jù)不同的操作和控制計(jì)劃，這種風(fēng)力發(fā)電機(jī)組可以吸收或輸出無功功率控制電壓，有利于電壓穩(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(fēng)力發(fā)電場使用的無功補(bǔ)償方法有關(guān)。</p><p><b>　?。?）電能質(zhì)量。</b></p&g

21、t;<p>　　風(fēng)力發(fā)電的波動(dòng)和相關(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(dòng)，可能會(huì)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(biāo)準(zhǔn)。在連續(xù)的運(yùn)行和開關(guān)操作，風(fēng)力發(fā)電機(jī)組，引起電壓波動(dòng)和閃爍，這些因素是風(fēng)力發(fā)電影響電網(wǎng)電能質(zhì)量的主要因素。對(duì)于變速風(fēng)力渦輪機(jī)和恒定頻率，轉(zhuǎn)換器造成的諧波問題，也應(yīng)考慮。</p><p>　　風(fēng)力渦輪機(jī)對(duì)電網(wǎng)干擾有不同的原因，其中大多

22、原因是風(fēng)力機(jī)本體。有關(guān)參數(shù)列于表1[10]。平均發(fā)電量，湍流強(qiáng)度及風(fēng)切變與氣象和地理?xiàng)l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(diǎn)，如發(fā)電機(jī)，變壓器等，也是轉(zhuǎn)子和傳動(dòng)系統(tǒng)的空氣動(dòng)力學(xué)和機(jī)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(duì)風(fēng)力渦輪機(jī)和風(fēng)力發(fā)電場的電能質(zhì)量特性有重要性。</p><p>　　表1.風(fēng)力發(fā)電機(jī)和風(fēng)力發(fā)電廠對(duì)電網(wǎng)造成的影響</p><p>　　電

23、壓升高 電能生產(chǎn)</p><p>　　諧波 變頻器</p><p><b>　　晶閘管控制器</b></p><p>　　閃爍是由風(fēng)力發(fā)電機(jī)組的有功功率或無功功率的的波動(dòng)造成的。固定速度

24、的風(fēng)力發(fā)電機(jī)閃爍的主要原因是塔的尾流。而變速風(fēng)力發(fā)電機(jī)，平滑了快速功率波動(dòng)，塔的尾流不影響輸出功率。因此，變速風(fēng)力發(fā)電機(jī)組的閃爍一般比定速閃爍風(fēng)力發(fā)電機(jī)低。</p><p><b>　　（5）短路容量。</b></p><p>　　往往是大多數(shù)的風(fēng)力發(fā)電場遠(yuǎn)離負(fù)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(dāng)遠(yuǎn)的。有一常理說，長電距離，使電壓變化

25、較大，但短路問題少[11]。</p><p>　　然而，風(fēng)力發(fā)電場將能夠給未來的電力系統(tǒng)運(yùn)行的短路電流計(jì)算帶來越來越重要的影響。原因是雙重的。一個(gè)是上述的事實(shí)，風(fēng)力發(fā)電網(wǎng)站通常是遠(yuǎn)離的傳統(tǒng)的電力中心。這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(gè)完全不同的短路容量地圖。其他事實(shí)的原因是，今天，越來越多的風(fēng)力發(fā)電，特別是以所謂的大型風(fēng)力發(fā)電場（數(shù)百兆瓦）的形式。在風(fēng)電場大量的個(gè)別單位連接在一起，總代能力將大大

26、上升。</p><p>　　風(fēng)電場對(duì)相鄰節(jié)點(diǎn)短路能力有很大影響，然而對(duì)遠(yuǎn)離PCC節(jié)點(diǎn)的影響不大[9]。因此，當(dāng)具有大容量的風(fēng)場并入電網(wǎng)時(shí)，相鄰變壓器和交換機(jī)的容量可能需要增加。應(yīng)該進(jìn)一步研究的是如何判斷風(fēng)力發(fā)電對(duì)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)

27、定的標(biāo)準(zhǔn)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(fēng)力發(fā)電量總額的增加，其變化頻率輸出是一個(gè)很重要的影響[8]。</p><p><b>　　（7）保護(hù)。</b></p><p>　　電流在風(fēng)電場和電網(wǎng)之間的流動(dòng)是雙向的，這是在保護(hù)的設(shè)計(jì)和配置應(yīng)予以考慮的。無論風(fēng)力發(fā)電機(jī)采用何種發(fā)電機(jī)，風(fēng)電場的整合將增加電網(wǎng)故障水平，進(jìn)而影響原有的電

28、網(wǎng)保護(hù)裝置繼電器的設(shè)置。這可能需要增加新的保護(hù)裝置或修改原有保護(hù)設(shè)備的繼電器的設(shè)置。尤其是如果風(fēng)電場連接到分配網(wǎng)絡(luò)，斷路器可能在風(fēng)電場裝機(jī)容量增加時(shí)產(chǎn)生超負(fù)荷[8]。</p><p>　　4、減輕風(fēng)力發(fā)電的影響的對(duì)策</p><p>　　無功補(bǔ)償設(shè)備的應(yīng)用，如靜止無功補(bǔ)償（SVC）和靜止同步補(bǔ)償器（STATCOM）在風(fēng)力發(fā)電中減輕其對(duì)電力系統(tǒng)的影響起著重要作用。為了保持電壓等級(jí)，電網(wǎng)公司可

29、以提供額外的或升級(jí)的電壓控制設(shè)施。無功補(bǔ)償設(shè)備應(yīng)該安裝在風(fēng)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(fēng)力發(fā)電造成的電壓波動(dòng)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大限度地減少了風(fēng)力發(fā)電機(jī)的輸出波動(dòng)，而風(fēng)力發(fā)電機(jī)的輸出最大化。同時(shí)，如在風(fēng)場安裝輔助設(shè)備SVC和儲(chǔ)能裝置也可以減輕電壓波動(dòng)和閃爍。在大多數(shù)情況下，快速作用無功補(bǔ)償設(shè)備，包括SVC和STATCOM，應(yīng)被納入為提高網(wǎng)絡(luò)的暫

30、態(tài)穩(wěn)定的設(shè)備之中。</p><p>　　從風(fēng)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(fēng)力發(fā)電的滲透。從電網(wǎng)方面，這對(duì)加強(qiáng)和改變目前的網(wǎng)絡(luò)具有重要意義。電壓源換流器系統(tǒng)（VSC）為基礎(chǔ)的高壓直流輸電（VSC-HVDC系統(tǒng)）是一個(gè)不需要任何額外賠償?shù)膫鬏斚到y(tǒng)，因?yàn)檫@是轉(zhuǎn)換器的控制固有的[13]。因此，它將是一個(gè)很好的工具，它使風(fēng)力發(fā)電成一個(gè)網(wǎng)絡(luò)，即使在一個(gè)弱網(wǎng)絡(luò)中，無需提高點(diǎn)短路比

31、，也能實(shí)現(xiàn)。VSC-HVDC的有功功率控制能力，然后是一個(gè)完美的處理有源功率/頻率控制的工具。它有能力以一個(gè)很好的方式處理風(fēng)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><p><b>　　5、結(jié)論</b></p><p>　　距今25年，風(fēng)能已經(jīng)經(jīng)過很長的時(shí)間，它很可能會(huì)在未來20年繼續(xù)推進(jìn)。有許多關(guān)于整合風(fēng)力發(fā)電系統(tǒng)的運(yùn)作和發(fā)展的問題。

32、雖然風(fēng)力發(fā)電取代了產(chǎn)生相當(dāng)數(shù)量能量的傳統(tǒng)植物，關(guān)注點(diǎn)都集中在了風(fēng)力發(fā)電和電網(wǎng)之間的相互作用上。本文提供了一個(gè)概覽風(fēng)力發(fā)電對(duì)電力系統(tǒng)的影響和相應(yīng)的對(duì)策建議來處理這些問題，為了適應(yīng)風(fēng)在電力系統(tǒng)的發(fā)電。</p><p><b>　　參考文獻(xiàn)</b></p><p>　　[1] EWEA．Wind force 12[EB/OL]．</p><p>　　

33、[2] GWEC．Global wind energy markets continue to boom-2006 another record year[EB/OL]．</p><p>　　[3] Liu Yan，Wang Wei wind power information Technology，2007</p><p>　　[4] Burton T，Sharpe D，Jenkins

34、N，et al．Wind energy handbook[M]．Chichester：John Wiley & Sons Ltd，2001</p><p>　　[5] Bowden G J，Barker P R，Shestopal V O，et al．Weibull distribution function[J]．Wind Engineering，1983，7(2)：85-98</p>&

35、lt;p>　　[6] Fan Zhenyu，Enslin J H R．Challenges, principles and issues relating to the development of wind power in China[C]．IEEE PES PSCE，2006：748-754</p><p>　　[7] O'Gorman R，Redfern M A．The difficulti

36、es of connecting renewable generation into utility networks[C]．IEEE Power Engineering Society General Meeting，2003，3：1466-1471</p><p>　　[8] Wang Wei sheng，Chen Mozi．Towards the integrating wind power into po

37、wer grid in China[J]．Electricity，2004，(4)：49-53</p><p>　　[9] Chi Yong ning，Liu Yan hua，Wang Wei sheng，et al．Study on impact of wind power integration on power system[J]．Power System Technology，2007，31(3)：77-

38、81</p><p>　　[10] Ackermann T．Wind power in power systems[M]．Chichester：John Wiley & Sons Ltd，2005</p><p>　　[11] Kumano T．A short circuit study of a wind farm considering mechanical torque fl

39、uctuation[C]．IEEE Power Engineering Society General Meeting，2006：1-6</p><p>　　[12] Strbac G，Shakoor A，Black M，et al．Impact of wind generation on the operation and development of the UK electricity systems[J]

40、．Electric Power Systems Research，2007，77(9)：1214-1227</p><p>　　[13] Eriksson K，Liljegren C，Sobrink K．HVDC light experience sapplicable for power transmission from offshore wind power parks[EB/OL]．</p>

41、<p><b>　　附件2：外文原文</b></p><p>　　Influence Research of Wind Power Generation on Power Systems</p><p>　　Jane Austen，Kurt Felix</p><p>　?。⊿tate Key Lab of Control and

42、Simulation of Power Systems and Generation Equipments，Manhattan District，New York，United States）</p><p>　　Abstract: Wind power generation is always weather dependent and has the trend of being integrated to

43、power systems as the form of large-scale wind farms, which influences on power systems. Since the power network was not designed specifically to accommodate this type of generation, there are inevitably some points at wh

44、ich modifications must be executed if existing standards of electricity supply are to be maintained. This paper discusses in general terms the problems which are encountered by th</p><p>　　Key Words: wind po

45、wer generation；power system；influence；wind farms</p><p>　　0．Introduction</p><p>　　There is widespread acceptance that renewable generation is the future of electricity supply. Generation based o

46、n fossil fuels is not sustainable as power electricity is being consumed rapidly. On the contrary, wind power has attracted much attention as a promising renewable energy resource. It has potential benefits in curbing em

47、issions and reducing the consumption of irreplaceable fuel reserves when the demand for power electricity has been steadily growing due to the industrial developments a</p><p>　　Wind power generation is beco

48、ming more and more popular while the large-scale wind farm(hundreds of megawatts) is the mainstream one. During 2006, the world’s installed wind capacity reached 74 223 MW, up from 59 091 MW in 2005,which include wind en

49、ergy developments in more than 70 countries around the world. The tremendous growth in 2006 shows that decision makers are starting to take seriously the benefits that wind energy development can bring.</p><p&

50、gt;　　There are no technical, economic or resource barriers to supplying 12% of the world’s electricity needs with wind power alone by 2020, and this against the challenging backdrop of a projected two thirds increase of

51、electricity demand by that date. The report is a crucial tool in the race to cut greenhouse gas emissions as 12% electricity from a total of 1 250 GW of wind power installed by 2020 will save a cumulative 10771 million t

52、ons of CO2[1].</p><p>　　Large-scale wind farms connected to power systems have characteristics of high capacity, dynamic and stochastic performance, which challenges system security and reliability. While pr

53、oviding the clean power for power systems, wind farms will also bring about some unfavorable influence on power systems. With the expansion of wind power generation and the increase of wind power ratio in a power system,

54、 the influence will likely become the technical barriers for wind power integration. Therefore, t</p><p>　　According to the issues mentioned above, this paper discusses in general terms the problems which ar

55、e encountered by the developers of wind power generation projects and by utility grids when dealing with projects to integrate wind farms to power systems. Due to the characteristics of high-capacity, dynamic and stochas

56、tic performance of wind power generation, the influence includes active and reactive power flow, voltage, system stability, power quality, short-circuit capacity, system reserve, f</p><p>　　1．Development sit

57、uation of wind power generation</p><p>　　From the report of the Global Wind Energy Council (GWEC), the countries with the highest total installed capacity are Germany (20 621 MW), Spain (11 615MW), the USA (

58、11603MW), India(6270 MW) and Denmark (3 136 MW). Thirteen countries around the world can now be counted among those with over 1000 MW of wind capacity, with France and Canada reaching this threshold in 2006. Fig.1 shows

59、the top 10 cumulative installed capacity of the world until December, 2006[2].</p><p>　　China started to develop wind power very late. It stepped into the stage of commercialized development and scale constr

60、uction only in 1990s. Accumulated and newly added installed generating capacity over the years is shown in Fig.2.The single-unit capacity increased from 100 kW, 200 kW, and 300 kW to 600 kW, 750 kW, and 1500 kW step by s

61、tep.</p><p>　　Fig. 1 Top 10 cumulative installed capacity of the world until December,2006</p><p>　　Fig. 2 Accumulative and newly-added installed capacity of wind power in China</p><p

62、>　　China doubled more than its total installed capacity by installing 1 347 MW of wind energy in 2006, a 70% increase from last year’s figure. This brings China up to 2 604 MW of capacity, making it the sixth largest

63、market world wide. the Chinese market has grown substantially in 2006, and this growth is expected to continue and speed up. According to the list of approved projects and those under construction, more than 1 500 MW wil

64、l be installed in 2007. The goal for wind power in China by the en</p><p>　　2．Characteristics of wind power generation</p><p>　　From the point of view of wind energy, the most striking character

65、istic of the wind resource is its variability. The stochastic variation of wind farms outputs root mainly in fluctuation of the wind speeds and directions. The wind is highly variable, both geographically and temporally.

66、 Furthermore this variability persists over a very wide range of scales, both in space and time.</p><p>　　The wind speed varies continuously as a function of time and height. The time scales of wind variatio

67、ns are presented in Fig.3 as a wind frequency spectrum[4]. The turbulent peak is caused by gusts in the sub second to minute range. The diurnal peak depends on daily wind speed variations and the synoptic peak depends on

68、 changing weather patterns, which typically vary daily to weekly but include also seasonal cycles.</p><p>　　Fig. 3 Wind spectrum farm Brookhaven based on work by van der Hoven</p><p>　　From a po

69、wer system perspective, the turbulent peak may affect the power quality of wind power generation. The influence of turbulences on power quality depends very much on the turbine technology applied. Variable-speed wind tur

70、bines, for instance, may absorb short-term power variations by the immediate storage of energy in the rotating masses of wind turbine drive trains. That means that the power output is smoother than strongly grid-coupled

71、turbines, fixed-speed wind turbines. Diurnal and sy</p><p>　　Another important issue is the long-term variations of the wind resources. The wind speed up to the height of the hub should be known to calculate

72、 the wind farm output. A number of measurements of wind speeds show that wind speeds are mostly mild in a year; their probabilities between 0 and 25m/s are considerable; most of the average annual wind speeds subject to

73、the Wei bull distribution[5], as in formula(1).</p><p><b>　　(1)</b></p><p>　　where: v is average wind speed; k is shape parameter; c is scale parameter.</p><p>　　The rel

74、ationship between the wind turbine output Pw and the wind speed up to the height of the hub v can be expressed approximately as the curve of wind turbine’s outputs vs. wind speed or a subsection function, as in formula (

75、2).</p><p><b>　　(2)</b></p><p>　　where: Pw is rated output of the wind turbine; v is wind speed up to the height of the hub; VCI is cut-in wind speed; VCO is cut-out wind speed; VR i

76、s rated wind speed.</p><p>　　3．Influence of wind power generation on power systems</p><p>　　High penetration of wind power in the power systems faces fundamental technical limits with regard to

77、the integration of large-scale wind farms to the grid. The influence of wind power generation on power systems includes active and reactive power flow, voltage, system stability, power quality, short-circuit capacity, sy

78、stem reserve and infrastructure due to the characteristics of high-capacity, dynamic and stochastic performance of wind power generation. Technically, it influences the gird in t</p><p>　?。?）Active and React

79、ive Power Flow.</p><p>　　Wind power is a kind of intermittent and stochastic power source, which will complicate the power flow. Because many wind farms are built far away from load centers in order to captu

80、re more wind energy, there is always some obstacle of transmitting wind power. Some transmission or distribution lines and other electrical equipments may be over-loaded when the additional wind power generation is intro

81、duced. So it should be ensured that the interconnecting transmission or distribution lines will no</p><p>　　The methods utilized for analysis of conventional generators are certain and ignore the uncertainty

82、 of wind speed and load forecasts. Therefore, the probabilistic method is more suitable for wind power generation. This model is based on the wind speed distribution, such as formula (1). The constraints are described by

83、 probabilistic forms and the expected values of parameters, such as voltages and powers can be computed.</p><p>　?。?）Voltage Regulation.</p><p>　　Once a wind farm has identified its site, the po

84、int at which connection to the grid must be identified. Small wind farm can connect at lower voltage, thereby saving on switchgear, cable and transformer costs. If the size of the proposed development is too large to be

85、connected at the local distribution voltage, access to the transmission network at a higher voltage is required[7].</p><p>　　After failures, if the transient unstability does not occur in power systems, some

86、 wind turbines shut down due to their low voltage protections. Then outputs of wind farms decrease, which means that the power system lose reactive loads. Therefore the voltage levels climb up, even beyond the upper limi

87、ts of wind farms buses.</p><p>　　Capacitors are the common reactive power compensation methods. When voltage levels dropdown, the amount of compensation decreases much. However the reactive power demands inc

88、rease when the asynchronous machines are utilized in wind farms. So voltage levels drop down more, even beyond the lower limits of wind farms buses.</p><p>　　With the increase of wind power installed capacit

89、y in power systems, the variability of wind power generation causes variability of voltage level, particularly if integrated into the grid which might not be specifically designed to cater for the significant and possibl

90、y rapid load variations (compared with normal customer load variation) caused by highly variable wind power generation. Therefore, the regulatory measures are needed to maintain the voltage level in a specified range. Ho

91、wever, the </p><p>　?。?）System Stability.</p><p>　　In the power system with high wind power penetration, the transient stability, voltage stability and frequency stability are all influenced by

92、the wind power integration not only because the injection of wind power will change the power flow distribution, transferred power of each transmission line and total inertia of the whole power system, but also because t

93、he wind turbine generators perform differently in either steady-state or transient-state compared with the conventional synchronous machi</p><p>　　For current operation of wind farms, protections usually cut

94、 off the connections between wind farms and the grid when great disturbances occur. This is equivalent to arouse new generators tripping disturbance after the great disturbances. So the transient stability in such moment

95、 is very crucial, especially when large-scale wind farms are integrated. Compared the variable-speed wind turbine based on the doubly-fed induction generator (DFIG) with the fixed-speed wind turbine based on the inductio

96、</p><p>　　The fixed-speed wind turbine absorbs the reactive power when outputting the active power. The whole demand of a wind farm for the reactive power is considerable, which lead to the decrease of the v

97、oltage stability in the area near PCC. On the contrary, the variable-speed wind turbine based on DFIG has certain ability to control the reactive power. According to different operation and control schemes, this wind tur

98、bine can absorb or output the reactive power to control the voltage, which benefits</p><p>　　（4）Power Quality.</p><p>　　Fluctuations in the wind power and the associated power transport (AC or D

99、C), have direct consequences to the power supply quality. As a result, large voltage fluctuations may result in voltage variations outside the regulation limits, as well as violations on flicker and other power quality s

100、tandards. During the continuous operation and switching operation, wind turbine causes voltage fluctuation and flicker, which are main concerns of unfavorable influence of wind power generation on power qua</p>&l

101、t;p>　　The grid interferences of wind turbines or wind farms have different causes, which are mostly turbine-specific. The relevant parameters are listed in Tab.1[10]. Average power production, turbulence intensity and

102、 wind shear refer to causes that are determined by meteorological and geographical conditions. All the other causes are attributed not only by the characteristics of the electrical components, such as generators, transfo