畢業(yè)論文中英文翻譯

1、 畢業(yè)設計（論文）外文翻譯中文題目： 大型風電場的瞬時穩(wěn)定和模擬 英文題目：modelling and transient stability of large wind farms 姓 名： 學 號： 系 別： 專 業(yè)： 年 級： 2012 年 月 日modelling and transient stability of large wind farmsvladislav and hans knudsen and arne hejde nielsen and jorgen kaas pedersen and niels kjolstad poulsendepartments of elec

2、tric power engineering,technical university of denmark,building 325,dk2800 lyngby,vladislav demmark1.introductiondenmark has currently about 2300 mw wind power capacity in on-land and few offshore settings, which corresponds to more than 20% of power consumption(in average). further, construction of

3、 two large-scale offshore wind farms of 150 mw power capacity each has been announced. the first large offshore wind farm in denmark will be constructed at homs rev by the year 2002 in the area of the system operator eltra .this will be followed by the first in the area of the eastern danish system

4、operator ,elkraft system ,large offshore wind farm at rodsand by the year 2003.the installed capacity in on-land settings and in combined heat-power units(uhp)will increase as well, whilst the power production and control ability of the conventional power plants with respect to voltage and frequency

5、 are reduced . in the years to come ,the power production pattern in the danish power system will change from the power supply from conventional power plantsas it is known todayto a power supply mix, where about 30-40%of power consumption(in average) is covered by wind power. in other words, the pow

6、er technology will undergo changes from a well-known technology built-up about conventional power plants to a partly unknown technologywind power.in the year to come it will be focusing on maintaining power system stability and voltage stability, for example at a short circuit fault, ensuring power

7、supply safety and other important tasks as amount of wind power is drastically increasing. this situation makes it necessary to find solutions with respect to maintaining dynamic stability of the power system with large amount of wind power and its reliable operation. these solutions are based on a

8、number of requirements that are formulated with respect to operation of the large offshore wind farms and the external power system in case of failure events in the external system.the paper contains separate subjects dealing with design of windmills for large offshore applications and their control

9、 that shall be taken into account with respect to improving the short-term voltage stability.1. system stability requirements in terms of short-term voltage stability, the major goal is the voltage re-establishing after failure events in the power system with large amount of wind power. the transmis

10、sion system operator is responsible for maintaining power system stability and reliable power supply.as the situation is today, the majority of the danish windmills on-land are stall wind turbines equipped with conventional induction generators and ac-connected to the power system. in case of a shor

11、t circuit fault in the power system, those windmills are easily overspeeded and, then, automatically disconnected from the power system and stopped. such automatic disconnections will be very fast and ordered by the windmill protection system relay settings. when the on-land windmills are automatica

12、lly disconnected, there is no dynamic reactive compensation demands related to them, despite their large power capacity. when the voltage is re-established, the on-land windmills will be automatically re-connected to the power system in 10-15 min afterwards and continue their operation,the on-land w

13、indmill relay settings are decided by the windmill manufacturers or the windmill owners and these, as usual, cannot be changed by the transmission system operator.in case of the large offshore wind farms, the power system operator has formulated the specifications for connecting wind farm to transmi

14、ssion network. in accordance with the specifications, the voltage stability at failure events in the external power system shall be maintained without any sub-sequential disconnection of the large offshore wind farms. establishing dynamic reactive compensation of the large offshore wind farms can be

15、, therefore, necessary. the amount of dynamic reactive compensation depends, generally, on the windmill technology and in the wind farms and is influenced by the windmill electrical and mechanical parameters.in other countries, similar specifications may be found as the result of large incorporation

16、 of wind power into the local power system.3.wind farm model the windmill technology in offshore settings has to be robust, developed and known practical applications. the wind turbine concept with conventional induction generators has been in operation in on-land settings in denmark during many yea

17、rs, which is why it may be considered that this technology will be used offshore as well. the wind turbines are equipped with blade angle control system-pitch or active stall that make it possible to adjust the set-points of the wind turbines by the blade by the blade angle adjustments.the complete

18、representation of the wind farm is chosen because the commonly asked question concerning large wind farms is whether there can be electromechanical interaction between a large number of the closely placed windmills excited by disturbances in the power system when the windmills are working at differe

19、nt set-points, equipped with relatively soft shafts and even having different mechanical data, and equipped with control systems, for instance pitch.the model of the offshore wind farm is implemented in the dynamic simulation tool pss/e and consists of 80 wind turbines of 2mw power capacity each, se

20、e fig.1.each wind turbine is simulated by a physical windmill model consisting of :1. the induction generator model with representation of the stator transients,2. the windmill shaft system model,3. the aerodynamic model of the wind turbine,4. the pitch control system given by the control logic and

21、the blade servo. for computation of wind turbine aerodynamics there are used airfoil data for a 2 mw pitch windmill equipped with an induction generator.each wind turbine is via its 0.7 kv/30kv connected to the wind farm internal network. the internal network is organised in eight rows with 10 wind

22、turbines in each row. within the rows, the wind turbines are connected through the 30 kv sea cables. the distance between two wind turbines in the same row is 500 m and the distance between two rows is 850 m.the rows are through the 30 kv sea cables connected to the offshore platform with 30 kv/132

23、kv transformer and, then, through the 132 kv sea/underground cable to the connection point in the transmission system on-land. there is chosen an ac-connection of the offshore wind farm to the transmission network.an irregular wind distribution over the wind farm area there is assumed since the wind

24、 turbines are shadowing each other for incoming wind. the efficiency of the wind farm is 93%at the given wind distribution and the power production pattern is shown in fig.1.furthermore, the windmill induction generators have a little different short circuit capacities viewed from their terminals in

25、to the internal network and this is why the wind turbine initial set-points are different.the short circuit capacity from the wind farm connection point into the transmission network is 1800 mva. in all the simulating examples, the failure event is a short circuit fault in the transmission system of

26、 150 ms of duration. when the fault is cleared, the faulted line is tripped and the short circuit capacity is reduced to 1000mva. only the line tripping and, then, reducing of the short circuit capacity to 1000mva does not lead to voltage instability. this ensures that possible voltage instability i

27、s only the result of the short circuit fault with the following windmill overspeeding.4. dynamic reactive compensationin this work, the dynamic reactive compensation of the large offshore wind farm is a svc of the capacity that will be necessary for maintaining the short-term voltage stability. the

28、model of the svc is as in ref. 5when operating as stall windmillsblade angle control is primarily used for optimization of the wind turbine mechanical power with respect to incoming wind and hence, this control ability is not necessarily available at failure events in external power system with resp

29、ect maintaining the short-term voltage stability. this implies that the pitch or active stall wind turbines may operate as conventional (passive)stall wind turbines, by the same way as windmills on-land, with the exception that they may not be disconnected.as the basis case with respect to the offsh

30、ore wind turbine data, the rotor winding resistance , the generator inertia ,the mill inertia , and the shaft stiffness ,see appendix a.if no dynamic reactive compensation is applied, a short circuit fault and a pose-fault line tripping will result in voltage instability, see fig.2. the windmills wi

31、ll be, then , tripped by the protective relays and power reserves of approx. 150 mw shall be found immediately.for voltage re-establishing after the short circuit fault, it will be necessary to use 100 mvar of dynamic reactive compensation. the simulated curves for the voltages and speeds are given

32、in fig.3.it is noticed that the wind turbine dynamic properties such as the voltage, the generator speed etc, show a fluctuating behaviour in the windmill drive-train system.despite the wind turbines have different initial set-points, the windmills show a coherent response at the failure event in th

33、e external network so that the fluctuations are in-phase and at the same frequency. the fluctuation frequency is the torsional mode of the windmill shafts.when the voltage is re-established, fluctuations in any electrical or mechanical properties are no longer seen. there is no self-excitation of th

34、e wind farm with a large number of wind turbines equipped with induction generators because the induction generators are passive systems in that no synchronizing torque and fast control have been applied.6. dynamic stability improvements within conventional technology the movement equation of a wind

35、mill in terms of the lumped-mass system is , (1a)where and are the mechanical torque of the rotating mill and the electric torque, respectively, and is the lumped-mass system speed (1b)where and are the mill mechanical speed and the electric speed of the generator, respectively, and at the given win

36、d, w.the dynamic stability limit of the windmill is found from the movement equations (1a) and (1b) as the speed above the kip-speed where . this solution is the critical speed of the windmill, , so that exceeding the critical speed, , leads to protective disconnection of windmills caused by overspe

37、eding (prevention of voltage instability). theoretical explanation for this definition can be found in ref. and its graphical illustration is shown in fig.4. from the definition of the dynamic stability limit, a number of stability improvement methods can be introduced in terms of conventional windm

38、ill technology that are given in the following.6.1. generator parametersthe shape of the electric torque versus speed curve, , is influenced by the windmill induction generator parameters in accordance with where is the windmill generator terminal voltage as a function of the generator speed, and th

39、e machine impedance with is given by the induction generator electrical parameters such as the stator resistance, , the stator reactance, , the magnetizing reactance, , the rotor resistance, ,and the rotor reactance, as given in ref.the short-term voltage stability will be always improved when the c

40、ritical speed of the windmill is expanded. this can be reached when:1. the values of and are reduced,2. the value of the rotor resistance, ,is increased.graphically this is illustrated in case of increasing the rotor resistance value, ,is increasing the rotor resistance value, ,see fig.4.increasing

41、the rotor resistance by the factor of 2, as in the example, leads to significant expanding of the critical windmill speed, and the dynamic reactive compensation demands are reduced significantly. when the rotor resistance is , there will only be necessary to use 25mvar dynamic reactive compensation

42、the voltage in the wind farm connection point is shown in fig.5.the 25mvar dynamic reactive compensation shall be compared with the reactive compensation demands in case of the rotor resistance value of that are in section 5 found to be 100mvar. the dynamic reactive compensation demands are reduced

43、significantly. on the other hand, this solution leads to increasing the power losses in the rotor circuit when the power system is in normal operation as well.6.2 enforcing mechanical construction it is a common opinion that when the inertia of the rotating system is higher, the more stable operatio

44、n is expected in the power system in post-fault situations.in terms of the dynamic stability limit definition, the inertia value does not influence on the windmill critical speed. two wind turbines with identical generator data and different inertia values and, where , have the same critical speed v

45、alues .due to different inertia values, the wind turbines will, however, accelerate differently at the failure event and hence, have the different critical failure times . because of this, the heavy wind turbines show more stable behaviour compared with tinny wind turbines, as long as the failure ti

46、me is not too long.in practical situations, the failure time is short enough and the heavy wind turbines will be preferred with respect to maintaining the voltage stability. windmills are equipped with the shaft systems where the effective shaft stiffness viewed from the generator terminals is relat

47、ively low .in normal operation, there will be accumulated an amount of potential energy in the shafts and the lower the shaft stiffness is, the more the potential energy accumulated is .at a short circuit fault, the shafts are relaxing and the potential energy is disengaged into the generator rotor

48、kinetic energy. this results in the more intensive acceleration of the generator rotor. the contribution to the generator rotor speed caused by the shaft relaxation is .increasing the shaft stiffness, k, leads, therefore, to the reduction of the windmill overspeeding at failure events, see fig.6, an

49、d hence, to the improvements of short-term voltage stability, in accordance with the dynamic stability limit considerations.the simulation results dealing with dynamic reactive compensation demands at varying parameters of the windmill mechanical construction,and,are collected in table 1.enforcement

50、 of the windmill mechanical construction has a significant positive effect on improvement of the short-term voltage stability.literature origin: international journal of electrical power & energy systems大型風電場的瞬時穩(wěn)定和模擬弗拉迪斯拉夫、漢斯克努森、阿恩尼爾森、約爾根卡斯佩德森、尼爾斯波爾森丹麥，弗拉迪斯拉夫，325，丹麥技術大學，電力工程系1介紹丹麥當前在陸地和極少海外的放置中有大約23

51、00 mw風能，這已經超過了平均能量消費水平的20% 。此外， 二個150 mw的大規(guī)模海面風電廠的工程已經被宣布。 在丹麥的第一個大的海面風電廠 2002 年以前將會在敘利亞被建造，它是系統(tǒng)操作員 eltra 的區(qū)域。這將會在東方丹麥的系統(tǒng)區(qū)域中被第一個跟隨操作員 ,elkraft 系統(tǒng)在2003 年以前就向海面的風電廠轉變。 在陸地放置中的和在結合的熱量單元( uhp )中的安裝的能力也將增加 ，在關于電壓和頻率的能量的生產和傳統(tǒng)發(fā)電廠的控制能力被減少的時候。 在未來的數年內，丹麥的電力制度的電力生產式樣將會從來自傳統(tǒng)電力補給改變，當現在對大約 30-40% 耗電量 (平均的) 被風能覆蓋

52、的一個動力補給混合的之時。換句話說，動力技術將會接受被建造的來自一種眾所周知的技術的變化，增加有關對部分未知的技術風動力的傳統(tǒng)發(fā)電廠。在這一年來它將著重于保持電力系統(tǒng)穩(wěn)定和電壓穩(wěn)定, 舉例來說在一個短路中, 當風動力的數量大幅增加的時候，確定電力供應安全和其他的重要工作就是必需解決的，就需要用大量的風能和它的可靠操作維持電力系統(tǒng)的動態(tài)穩(wěn)定。2. 系統(tǒng)穩(wěn)定需求 根據短期的電壓穩(wěn)定，主要的目標是在發(fā)生故障之后以大量的風能恢復電壓。 傳輸系統(tǒng)操作員負責維持電力系統(tǒng)穩(wěn)定和可靠的電力供應。今天，丹麥陸地上的多數風車是風力機裝備著異步發(fā)電機并且直接并網。假使一個電力系統(tǒng)的過失短路, 那些風車就容易地被超速

53、, 然后, 自動地從電力系統(tǒng)中分離而且停止。 如此自動的切斷將會非?？焖俣冶仨毐伙L車保護制度接替者設定。當那在陸地上的風車自動地被分離,沒有動態(tài)的起反作用的補償要求涉及到它們。 當電壓是恢復后, 在陸地上風車將會再自動地然后被連接到電網在 10-15 分鐘中的力量制度而且繼續(xù)它們的運轉。陸地上的風車繼電器設定被風車制造業(yè)者決定或者風車擁有者和這些, 像往常一樣，不能夠被傳輸系統(tǒng)操作員改變。假使大的海面風場，電力系統(tǒng)操作員已經制定把風場連結到傳輸網絡的規(guī)格。 符合規(guī)格，電壓穩(wěn)定性在外部系統(tǒng)故障時將會被維修在沒斷開大型海上風場。因此，建立海上風場動力起反作用的補償是必需的。 通常,大的動態(tài)反動的

54、補償靠風車技術上和在風場中而且被風電和機械參數影響。在其他國家,可以找到類似的規(guī)定,由于大型風力發(fā)電將成為當地電力系統(tǒng). 3.風場模型在海上設定的風車技術必須是強健的,發(fā)展和知名的實際應用。 帶異步發(fā)電機的風輪機觀念已經運轉在陸地風場的設定在丹麥這些年,是它可能為什么被視為將會被用在海上的技術。風力渦輪機葉片角度控制設有定位或活動檔,可以調整結構項的風力渦輪機葉片的調整來完成.海面風農場的模型在動態(tài)的模擬工具 pss/e 中被實現，而且有 2mw 發(fā)電容量的 80個用來發(fā)電的風車, 見 圖1。風力渦輪機是由每一個物理模擬模型風車包括: （1）適應模式與發(fā)電機定子的旅客代表、 （2）風車槽系統(tǒng)的

55、模式 （3）風力渦輪的氣動模型, （4）由于球的控制系統(tǒng),完成伺服控制邏輯.風農場的完全表示法被選擇，因為共同地被問的問題關于大風農場是否在動力系統(tǒng)可以有干擾激發(fā)的很大數量的嚴密被安置的風車之間的機電互作用，當風車運轉在不同的設置點時。裝備相對地軟的軸和平衡有另外機械數據和裝備以控制系統(tǒng)，例如瀝青。為風渦輪空氣動力學的計算有老的機翼數據為一臺2兆瓦風車裝備異步電動機。每個風渦輪是通過它的0.7 kv/30kv連接到風場內部網絡。 內部網絡在八列在每列被組織與10個機。 在列之內， 風輪機通過30千伏海底電纜連接。 二個風渦輪之間的距離在同一列是500 m，并且二列之間的距離是850 m。該列是

56、通過30千伏海底電纜連接到近海平臺用30 kv/132千伏變壓器， 然后， 通過132千伏海地下電纜對連接點在傳動陸地系統(tǒng)。 海上風場選擇了交流連接到傳輸網絡。一種不規(guī)則的風力分布在風場,由于假設是跟蹤對方的風力渦輪風來襲. 風場風輪機效率的93%,分布在特定的風力發(fā)電方式顯示圖1。此外,風車發(fā)電機入門有點短路能力從不同的終端進入內部網絡,這就是最初的風力渦輪點不同.短路容量從風場連接點到傳輸網絡里是1800 mva。在所有模仿的例子，失敗事件是短路缺點在期間的有持續(xù)150ms的傳動系統(tǒng)。當故障清除，故障線路強度大，并且短路容量減少到1000mva。僅線路流暢和減少短路容量到1000mva, 不會導致電壓不穩(wěn)定。這保證可能的電壓不穩(wěn)定僅僅是因風車超速短路而引起的結果。4. 動態(tài)的電抗補償這方面的工作,有力反應補償近海風力大農場是svc的能力,有必要保