毕业论文中英文翻译

1、 毕业设计（论文）外文翻译中文题目： 大型风电场的瞬时稳定和模拟 英文题目：modelling and transient stability of large wind farms 姓 名： 学 号： 系 别： 专 业： 年 级： 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大型风电场的瞬时稳定和模拟弗拉迪斯拉夫、汉斯克努森、阿恩尼尔森、约尔根卡斯佩德森、尼尔斯波尔森丹麦，弗拉迪斯拉夫，325，丹麦技术大学，电力工程系1介绍丹麦当前在陆地和极少海外的放置中有大约23

51、00 mw风能，这已经超过了平均能量消费水平的20% 。此外， 二个150 mw的大规模海面风电厂的工程已经被宣布。 在丹麦的第一个大的海面风电厂 2002 年以前将会在叙利亚被建造，它是系统操作员 eltra 的区域。这将会在东方丹麦的系统区域中被第一个跟随操作员 ,elkraft 系统在2003 年以前就向海面的风电厂转变。 在陆地放置中的和在结合的热量单元( uhp )中的安装的能力也将增加 ，在关于电压和频率的能量的生产和传统发电厂的控制能力被减少的时候。 在未来的数年内，丹麦的电力制度的电力生产式样将会从来自传统电力补给改变，当现在对大约 30-40% 耗电量 (平均的) 被风能覆盖

52、的一个动力补给混合的之时。换句话说，动力技术将会接受被建造的来自一种众所周知的技术的变化，增加有关对部分未知的技术风动力的传统发电厂。在这一年来它将着重于保持电力系统稳定和电压稳定, 举例来说在一个短路中, 当风动力的数量大幅增加的时候，确定电力供应安全和其他的重要工作就是必需解决的，就需要用大量的风能和它的可靠操作维持电力系统的动态稳定。2. 系统稳定需求 根据短期的电压稳定，主要的目标是在发生故障之后以大量的风能恢复电压。 传输系统操作员负责维持电力系统稳定和可靠的电力供应。今天，丹麦陆地上的多数风车是风力机装备着异步发电机并且直接并网。假使一个电力系统的过失短路, 那些风车就容易地被超速

53、, 然后, 自动地从电力系统中分离而且停止。 如此自动的切断将会非常快速而且必须被风车保护制度接替者设定。当那在陆地上的风车自动地被分离,没有动态的起反作用的补偿要求涉及到它们。 当电压是恢复后, 在陆地上风车将会再自动地然后被连接到电网在 10-15 分钟中的力量制度而且继续它们的运转。陆地上的风车继电器设定被风车制造业者决定或者风车拥有者和这些, 像往常一样，不能够被传输系统操作员改变。假使大的海面风场，电力系统操作员已经制定把风场连结到传输网络的规格。 符合规格，电压稳定性在外部系统故障时将会被维修在没断开大型海上风场。因此，建立海上风场动力起反作用的补偿是必需的。 通常,大的动态反动的

54、补偿靠风车技术上和在风场中而且被风电和机械参数影响。在其他国家,可以找到类似的规定,由于大型风力发电将成为当地电力系统. 3.风场模型在海上设定的风车技术必须是强健的,发展和知名的实际应用。 带异步发电机的风轮机观念已经运转在陆地风场的设定在丹麦这些年,是它可能为什么被视为将会被用在海上的技术。风力涡轮机叶片角度控制设有定位或活动档,可以调整结构项的风力涡轮机叶片的调整来完成.海面风农场的模型在动态的模拟工具 pss/e 中被实现，而且有 2mw 发电容量的 80个用来发电的风车, 见 图1。风力涡轮机是由每一个物理模拟模型风车包括: （1）适应模式与发电机定子的旅客代表、 （2）风车槽系统的

55、模式 （3）风力涡轮的气动模型, （4）由于球的控制系统,完成伺服控制逻辑.风农场的完全表示法被选择，因为共同地被问的问题关于大风农场是否在动力系统可以有干扰激发的很大数量的严密被安置的风车之间的机电互作用，当风车运转在不同的设置点时。装备相对地软的轴和平衡有另外机械数据和装备以控制系统，例如沥青。为风涡轮空气动力学的计算有老的机翼数据为一台2兆瓦风车装备异步电动机。每个风涡轮是通过它的0.7 kv/30kv连接到风场内部网络。 内部网络在八列在每列被组织与10个机。 在列之内， 风轮机通过30千伏海底电缆连接。 二个风涡轮之间的距离在同一列是500 m，并且二列之间的距离是850 m。该列是

56、通过30千伏海底电缆连接到近海平台用30 kv/132千伏变压器， 然后， 通过132千伏海地下电缆对连接点在传动陆地系统。 海上风场选择了交流连接到传输网络。一种不规则的风力分布在风场,由于假设是跟踪对方的风力涡轮风来袭. 风场风轮机效率的93%,分布在特定的风力发电方式显示图1。此外,风车发电机入门有点短路能力从不同的终端进入内部网络,这就是最初的风力涡轮点不同.短路容量从风场连接点到传输网络里是1800 mva。在所有模仿的例子，失败事件是短路缺点在期间的有持续150ms的传动系统。当故障清除，故障线路强度大，并且短路容量减少到1000mva。仅线路流畅和减少短路容量到1000mva, 不会导致电压不稳定。这保证可能的电压不稳定仅仅是因风车超速短路而引起的结果。4. 动态的电抗补偿这方面的工作,有力反应补偿近海风力大农场是svc的能力,有必要保