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1、Dynamic modeling and direct power control of wind turbine driven DFIG under unbalanced network voltage conditionAbstract: This paper proposes an analysis and a direct power control (DPC) design of a wind turbine driven doubly-fed induction generator(DFIG)under unbalanced network voltage conditions.

2、A DFIG model described in the positive and negative synchronous reference frames is presented. Variations of the stator output active and reactive powers are fully deduced in the presence of negative sequence supply voltage and rotor flux. An enhanced DPC scheme is proposed to eliminate stator activ

3、e power oscillation during network unbalance. The proposed control scheme removes rotor current regulators and the decomposition processing of positive and negative sequence rotor currents. Simulation results using PSCAD/EMTDC are presented on a 2-MW DFIG wind power generation system to validate the

4、 feasibility of the proposed control scheme under balanced and unbalanced network conditions.Key words: Doubly-fed induction generator (DFIG) Wind turbine, Direct power control (DPC), Stator voltage oriented (SVO), Unbalanced networkINTRODUCTION,Wind farms based on the doubly-fed induction generator

5、s (DFIG) with converters rated at 25%30%of the generator rating for a given rotor speed variation range of25%are becoming increasingly popular. Compared with the wind turbines using fixed speed induction generators or fully-fed synchronous generators with full-size converters the DFIG-based wind tur

6、bines offer not only the advantages of variable speed operation and four-quadrant active and reactive power capabilities, but also lower converter cost and power losses (Pena et al., 1996).However, both transmission and distribution networks could usually have small steady state and large transient

7、voltage unbalance. If voltage unbalance is not considered by the DFIG control system, the stator current could become highly unbalanced even with a small unbalanced stator voltage. The unbalanced currents create unequal heating on the stator windings, and pulsations in the electromagnetic torque and

8、 stator output active and reactive powers(Chomatetal.,2002;Jang et al.,2006;Zhou et al.,2007;Pena et al., 2007;Hu et al.,2007;Xu and Wang,2007;Hu and He,2008).Control and operation of DFIG wind turbine systems under unbalanced network conditions is traditionally based on either stator-flux-oriented(

9、SFO)(Xu and Wang,2007)or stator-voltage-oriented(SVO)vector control(Jang et al.,2006;Zhou et al.,2007;Hu et al.,2007;Hu and He,2008).The scheme in(Jang et al.,2006;Zhou et al.,2007;Xu and Wang,2007;Hu et al.,2007)employs dual-PI(proportional integral)current regulators implemented in the positive an

10、d negative synchronously rotating reference frames, respectively, which has to decompose the measured rotor current into positive and negative sequence components to control them individually. One main drawback of this approach is that, the time delays introduced by decomposing the sequential compon

11、ents of rotor current can affect the overall system stability and dynamic response. Thus, a current control scheme based on a proportional resonant(PR)regulator in the stator stationary reference frame was proposed in(Hu and He,2008), which can directly control the rotor current without the need of

12、sequential decomposition. Whereas, the performance of the vector control scheme highly depends on the accurate machine parameters such as stator/rotor inductances and resistances used in the control system.Similar to direct torque control (DTC) of induction machines presented a few decades ago, whic

13、h behaves as an alternative to vector control, direct power control (DPC)of DFIG-based wind turbine systems has been proposed recently(Gokhaleet al.,2002;Xu and Cartwright,2006;Zhi and Xu,2007). In (Gokh a le et al., 2002), the control scheme was based on the estimated rotor flux. Switching vectors

14、were selected from the optimal switching table using the estimated rotor flux position and the errors of rotor flux and active power. The rotor flux reference was calculated using the reactive power reference. Since the rotor supply frequency, equal to the DFIG slip frequency, might be very low, the

15、 rotor flux estimation could be significantly affected by the machine parameter variations. In (Xu and Cartwright,2006),a DPC strategy based on the estimated stator flux was proposed. As the stator voltage is relatively harmonics-free and fixed in frequency, a DFIG estimated stator flux accuracy can

16、 then be guaranteed. Switching vectors were selected from the optimal switching table using the estimated stator flux position and the errors of the active and reactive powers. Thus, the control system was simple and the machine parameters impact on the system performance was found to be negliable.

17、However, like a conventional DTC, DPC has the problem of unfixed switching frequency, due to the significant influence of the active and reactive power variations, generator speed, and power controllers hysteresis bandwidth. More recently, a modified DPC strategy has been proposed in (Zhi and Xu, 20

18、07) based on SFO vector control in the synchronous reference frame for DFIG-based wind power generation systems with a constant switching frequency. The control method directly calculates the required rotor control voltage within each switching period, based on the estimated stator flux, the active

19、and reactive powers and their errors. The control strategy provides improved transient performance with the assumption of the stator (supply) voltage being strictly balanced. However, the operation could be deteriorated during the supply voltage unbalance and there is no report yet on DFIG DPC under

20、 unbalanced network voltage conditions.This paper investigates an improved DPC scheme for a DFIG wind power generation system under unbalanced network conditions. In the SVO dq reference frame, a mathematical DPC model of a DFIG system with balanced supply is presented, which is referred to as the c

21、onventional model in this paper. Then during network unbalance, a modified DFIG DPC model in the SVO positive dq and negative dq reference frames is developed .Based on the developed model, a system control strategy is proposed by eliminating the stator output active power oscillations under unbalan

22、ced network conditions. Finally, simulation results on a 2-MW DFIG wind generation system are presented to demonstrate the correctness and feasibility of the proposed control strategy.SIMULATION STUDIES,Simulations of the proposed DPC strategy for a DFIG-based wind power generation system were condu

23、cted using PSCAD/EMTDC. A single-phase load at the primary side of the coupling transformer was used to generate the voltage unbalance. The nominal DC link voltage was set at 1 200 V and the switching frequencies for both converters were 2 000 Hz. The main target of the grid side converter was assig

24、ned to control the DC link voltage with the similar method used in(Song and Nam,1999;Hu et al.,2007).As shown in Fig.7,a high frequency AC filter is shunt-connected to the stator side to absorb the switching harmonics generated by the twoconverters. Initial studies with various active and reactive p

25、ower steps were carried out to test the dynamic response using the conventional control scheme shown in Fig.4 in the conditions of balanced supply voltage. First, the DFIG was assumed to be in speed control, viz., the rotor speed was set externally, as the large inertia of the wind turbine resulting

26、 in a slow change of the rotor speed. The active and reactive powers were initially set at 0 MW and0.5 MVA, respectively, where refers to absorbing reactive power. Various power steps were applied, viz., active and reactive power references were changed from 0 to2 MW at the instant of 1.3 s. CONCLUS

27、ION，This paper has proposed an analysis and an improved DPC design for a DFIG-based wind power generation system during network voltage unbalance. Simulation results were presented to demonstrate the feasibility of the proposed control scheme. Conclusions can be drawn as follows: (1)The conventional

28、 DPC scheme without net-work unbalance considered can provide pretty good dynamic system performance when the supply voltage is strictly balanced. However, once the net-work is slightly unbalanced, the performance deteriorates with high stator/rotor current unbalances and significant oscillations in

29、 the stator active/reactive power and electromagnetic torque. (2)The proposed DPC scheme, which is implemented in the SVO positive dq+ and negative dq reference frames, gets rid of the decomposition process of positive and negative sequence rotor currents in the vector control scheme using dual-PI r

30、otor enhanced by the elimination of the stator output active power oscillations and the reduction of the electro-magnetic torque pulsations during network unbalance. 动态建模与驱动的双馈风力发电机直接供电网络的电压不平衡条件下的控制摘要：本文提出了一种分析和直接功率控制（DPC）的驱动的不平衡电网电压条件下双馈感应发电机（双馈）风力发电机组的设计。一个双馈模型中描述的正面和负面的同步提出了参考框架。变化的定子输出有功，无功的权力是

31、完全推导出的负序电压和转子磁链的存在。增强的DPC的计划，提出在网络，以消除不平衡定子有功功率振荡。建议中的管制机制将消除转子电流调节器和正，负序转子电流分解处理。仿真结果使用PSCAD / EMTDC的提出在2兆瓦双馈风力发电系统，以验证网络下的平衡和不平衡的状况下，提出的控制方案的可行性。关键词：双馈感应发电机（双馈）风力发电机组，直接功率控制（DPC），定子电压定向，非平衡网络 风力发电场的双馈感应发电机与转换器在2530给定转子速度变化范围 25额定发电机（双馈）的基础正在变得越来越受欢迎。相对于采用固定速异步风力发电机或完全够了全尺寸的转换器，同步发电机双馈型风力涡轮机不仅提供了变速

32、操作和四象限有功，无功功率能力涡轮机的优点，同时也降低转换器成本和功率损耗。然而，无论输配电网络通常可以有小的稳态和瞬态电压不平衡大。如果电压不平衡不是由双馈电机控制系统的考虑，定子电流极不平衡，甚至可能成为一个小定子电压不平衡。创建不平等的不平衡电流加热定子绕组，在电磁转矩和定子输出有功，无功权力。控制与双馈风力发电机组的条件下不平衡网络系统的运行是基于传统或定子磁场定向或定子电压导向矢量控制采用双皮（在正面和负面的同步旋转坐标系实施比例积分）电流调节器，分别具有测量转子分解为正，负序分量电流来控制它们。这种方法的一个主要缺点是，分解的时间序列的转子组件介绍当前的延误可能会影响整个系统的稳定

33、性和动态响应。因此，一个电流控制计划按比例谐振（PR）在定子静止坐标系的基础上，提出监管机构在它可以直接控制的顺序分解而不需要转子电流。鉴于，对矢量控制方案的性能，高度依赖于如定子/转子电感和电阻的精确控制系统中使用的机器参数。类似的直接转矩控制的感应电机器（DTC）提出了几十年前，它作为一个矢量控制的替代行为，直接功率控制（DPC）的的双馈型风力发电机组已经提出了近期该控制方案是基于转子磁通估计。交换载体选自最优开关使用转子磁通估计位置和转子磁通与有功功率表的错误。转子磁通参考乃采用无功功率的参考。由于转子供电频率，相当于双馈电机转差频率，可能非常低，转子磁通估计可能有重大影响的机床参数的变

34、化。对估计的定子磁链为基础，提出了DPC的战略。由于定子电压相对谐波和无频率固定，双馈电机定子磁链估计精度可以得到保证。交换载体选自最优开关利用估计定子磁链的位置和有功，无功权力的错误表。因此，控制系统简单，机器的参数对系统性能的影响被认为是不可靠的。然而，像传统的存款，缩节胺具有开关频率不固定的问题，由于对有功和无功功率的变化，发电机的转速和功率控制器的磁滞带宽显着影响。最近，修改后的DPC的战略已经提出根据证券及期货条例的双馈型风力发电具有恒定的开关频率同步发电系统矢量控制的参照系。该控制方法直接计算出每个开关周期内所需的旋翼控制电压的基础上，估计定子磁链，主动和被动的权力和他们的错误。该

35、控制策略提供了改善，与定子（供应）假设被严格平衡电压瞬态性能。但是，该操作可能会恶化，在电源电压不平衡，也没有对双馈DPC的报告网络的电压条件下还不平衡。本文研究了双馈风力发电的网络条件下的不平衡产生的DPC系统的改进方案。在主导方向的作用下，一个数学的DPC与供求平衡的双馈系统模型提出了一种被称为本文中的传统模式。然后在网络失衡，修改后的双馈缩节胺在高级兽医师正面和负面的电话号码查询电话号码查询参考框架模型。模型的基础上开发的，系统的控制策略，提出了消除了定子输出网络条件下的不平衡有功功率振荡。最后，在一个2兆瓦双馈风力发电系统的仿真结果的正确性，并证明该控制策略的可行性。拟议的DPC的双馈

36、型风力发电系统的策略进行了模拟使用PSCAD / EMTDC的。在一个耦合变压器一次侧单相负载是用来产生的电压不平衡。标称直流母线电压设定在1 200 V和两个转换器的开关频率为2 000赫兹。该电网侧变换器的主要目标是控制与分配使用的类似方法的直流母线电压。各种有功、无功功率的步骤进行了初步研究，以测试使用的动态响应常规的控制计划，图4所示的均衡供应电压的条件。首先，双馈被认为是速度控制，即，转子转速为外部设定为风在转子的速度缓慢变化引起的汽轮机大惯性。各种电源应用步骤，即，有功、无功引用从0变化到2的即时的1.3兆瓦。结论:本文提出了一种分析和改进的DPC的双馈型风力发电在电网电压不平衡的

37、系统设计。仿真结果提交证明该控制方案的可行性。可以得出结论如下：（1）传统的DPC没有网络工作考虑不平衡方案能提供不错的动力系统性能时，电源电压为严格平衡。但是，一旦网络工作稍有不平衡，性能恶化，高定子/转子电流不平衡，在定子有功/无功功率和电磁转矩显着振荡。 （2）拟议DPC的计划，这是高级兽医师积极的电话号码查询+和消极电话号码查询参照系实施，取得了积极和负序矢量控制方案的转子电流分解过程中摆脱使用双皮转子加强了消除定子输出有功功率振荡和电磁转矩脉动在网络不平衡量减少。 五分钟搞定5000字毕业论文外文翻译，你想要的工具都在这里!在科研过程中阅读翻译外文文献是一个非常重要的环节，许多领域高

38、水平的文献都是外文文献，借鉴一些外文文献翻译的经验是非常必要的。由于特殊原因我翻译外文文献的机会比较多，慢慢地就发现了外文文献翻译过程中的三大利器：Google“翻译”频道、金山词霸（完整版本）和CNKI“翻译助手。具体操作过程如下： 1.先打开金山词霸自动取词功能，然后阅读文献； 2.遇到无法理解的长句时，可以交给Google处理，处理后的结果猛一看，不堪入目，可是经过大脑的再处理后句子的意思基本就明了了； 3.如果通过Google仍然无法理解，感觉就是不同，那肯定是对其中某个“常用单词”理解有误，因为某些单词看似很简单，但是在文献中有特殊的意思，这时就可以通过CNKI的“翻译助手”来查询相

39、关单词的意思，由于CNKI的单词意思都是来源与大量的文献，所以它的吻合率很高。 另外，在翻译过程中最好以“段落”或者“长句”作为翻译的基本单位，这样才不会造成“只见树木，不见森林”的误导。四大工具： 1、Google翻译： google，众所周知，谷歌里面的英文文献和资料还算是比较详实的。我利用它是这样的。一方面可以用它查询英文论文，当然这方面的帖子很多，大家可以搜索，在此不赘述。回到我自己说的翻译上来。下面给大家举个例子来说明如何用吧比如说“电磁感应透明效应”这个词汇你不知道他怎么翻译，首先你可以在CNKI里查中文的，根据它们的关键词中英文对照来做，一般比较准确。 在此主要是说在google

40、里怎么知道这个翻译意思。大家应该都有词典吧，按中国人的办法，把一个一个词分着查出来，敲到google里，你的这种翻译一般不太准，当然你需要验证是否准确了，这下看着吧，把你的那支离破碎的翻译在google里搜索，你能看到许多相关的文献或资料，大家都不是笨蛋，看看，也就能找到最精确的翻译了，纯西式的！我就是这么用的。 2、CNKI翻译： CNKI翻译助手，这个网站不需要介绍太多，可能有些人也知道的。主要说说它的有点，你进去看看就能发现：搜索的肯定是专业词汇，而且它翻译结果下面有文章与之对应（因为它是CNKI检索提供的，它的翻译是从文献里抽出来的），很实用的一个网站。估计别的写文章的人不是傻子吧，它

41、们的东西我们可以直接拿来用，当然省事了。网址告诉大家，有兴趣的进去看看，你们就会发现其乐无穷！还是很值得用的。 3、网路版金山词霸（不到1M）： 4、有道在线翻译：翻译时的速度：这里我谈的是电子版和打印版的翻译速度，按个人翻译速度看，打印版的快些，因为看电子版本一是费眼睛，二是如果我们用电脑，可能还经常时不时玩点游戏，或者整点别的，导致最终SPPEED变慢，再之电脑上一些词典（金山词霸等）在专业翻译方面也不是特别好，所以翻译效果不佳。在此本人建议大家购买清华大学编写的好像是国防工业出版社的那本英汉科学技术词典，基本上挺好用。再加上网站如：google CNKI翻译助手，这样我们的翻译速度会提高

42、不少。具体翻译时的一些技巧（主要是写论文和看论文方面） 大家大概都应预先清楚明白自己专业方向的国内牛人，在这里我强烈建议大家仔细看完这些头上长角的人物的中英文文章，这对你在专业方向的英文和中文互译水平提高有很大帮助。 我们大家最蹩脚的实质上是写英文论文，而非看英文论文，但话说回来我们最终提高还是要从下大工夫看英文论文开始。提到会看，我想它是有窍门的，个人总结如下： 1、把不同方面的论文分夹存放，在看论文时，对论文必须做到看完后完全明白（你重视的论文）；懂得其某部分讲了什么（你需要参考的部分论文），在看明白这些论文的情况下，我们大家还得紧接着做的工作就是把论文中你觉得非常巧妙的表达写下来，或者是

43、你论文或许能用到的表达摘记成本。这个本将是你以后的财富。你写论文时再也不会为了一些表达不符合西方表达模式而烦恼。你的论文也降低了被SCI或大牛刊物退稿的几率。不信，你可以试一试 2、把摘记的内容自己编写成检索，这个过程是我们对文章再回顾，而且是对你摘抄的经典妙笔进行梳理的重要阶段。你有了这个过程。写英文论文时，将会有一种信手拈来的感觉。许多文笔我们不需要自己再翻译了。当然前提是你梳理的非常细，而且中英文对照写的比较详细。 3、最后一点就是我们往大成修炼的阶段了，万事不是说成的，它是做出来的。写英文论文也就像我们小学时开始学写作文一样，你不练笔是肯定写不出好作品来的。所以在此我鼓励大家有时尝试着把自己的论文强迫自己写成英文的，一遍不行，可以再修改。最起码到最后你会很满意。呵呵，我想我是这么觉得的。