附录A 英文参考文献
Dynamic modeling and direct power control of wind turbine driven DFIG under unbalanced network voltage condition INTRODUCTION,Wind farms based on the doubly-fed inductiongenerators(DFIG)with converters rated at 25%~30%ofthe generator rating for    a given rotor speedvariation range of±25%are becoming increasinglypopular.Compared with the wind turbines using fixedspeed induction generators or fully-fed synchronousgenerators with full-size convertersthe DFIG-basedwind turbines offer not only theadvantages of variable speed operation and four-quadrant active andreactive power capabilities,but also lower convertercost and power losses(Pena et al.,1996).However,both transmission and distribution networks couldusually have small steady state and large transientvoltage unbalance.If voltage unbalance is not considered by the DFIG control system,the stator currentcould become highly unbalanced even with    a smallunbalanced stator voltage.The unbalanced currentscreate unequal heating on the stator windings,andpulsations in the electromagnetic torque and statoroutput 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 andHe,2008).Control and operation of DFIG wind turbinesystems under unbalanced network conditions istraditionally based on either stator-flux-oriented(SFO)(Xuand 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).T
he schemein(Jang et al.,2006;Zhou et al.,2007;Xu and Wang,2007;Hu et al.,2007)employs dual-PI(proportionalintegral)current regulators implemented in thepositive and negative synchronously rotating referenceframes,respectively,which has to decompose themeasured rotor current into positive and negative sequence components to control them individually.One main drawback of this approach is that,the timedelays introduced by decomposing the sequentialcomponents of rotor current can affect the overallsystem stability and dynamic response.Thus,acurrent control scheme based on    a proportionalresonant(PR)regulator in the stator stationaryreference frame was proposed in(Hu and He,2008),which can directly control the rotor current withoutthe need of sequential decomposition.Whereas,theperformance of the vector control scheme highlydepends on the accurate machine parameters such asstator/rotor inductances and resistances used in thecontrol system.
Similar to direct torque control(DTC)ofinduction machines presented a few decades ago,which behaves as an alternative to vector control,direct power control(DPC)of DFIG-based windturbine systems has been proposed recently(Gokhaleet al.,2002;Xu and Cartwright,2006;Zhi and Xu,2007).In(Gokhale et al.,2002),the control schemewas based on the estimated rotor flux.Switchingvectors were selected from the optimal switchingtable using the estimated rotor flux position and theerrors of rotor flux and active power.The rotor fluxreference was calculated
using the reactive powerreference.Since the rotor supply frequency,equal tothe DFIG slip frequency,might be very low,the rotorflux estimation could be significantly affected by themachine parameter variations.In(Xu and Cartwright,2006),a DPC strategy based on the estimated statorflux was proposed.As the stator voltage is relativelyharmonics-free and fixed in frequency,a DFIGestimated stator flux accuracy can then be guaranteed.Switching vectors were selected from the optimalswitching table using the estimated stator fluxposition and the errors of the active and reactivepowers.Thus,the control system was simple and themachine parameters’impact on the systemperformance was found to be negli able.However,like a conventional DTC,DPC has the problem ofunfixed switching frequency,due to the significantinfluence of the active and reactive power variations,generator speed,and power controllers’hysteresisbandwidth.More recently,a modified DPC strategyhas been proposed in(Zhi and Xu,2007)based onSFO vector control in the synchronous referenceframe for DFIG-based wind power generationsystems with a constant switching frequency.The control method directly calculates the required rotorcontrol voltage within each switching period,basedon the estimated stator flux,the active and reactivepowers and their errors.The control strategy providesimproved transient performance with the assumptionof the stator(supply)voltage being strictly balanced.However,the operation could be deteriorated duringthe supply voltage unbalance and there is no reportyet on DFIGDPC under unbalanced networkvoltage conditions.
This paper investigates an improved DPCscheme for a DFIG wind power generation systemunder unbalanced network conditions.In the SVO dqreference frame,a mathematical DPC model of aDFIG system with balanced supply is presented,which is referred to as the conventional model in thispaper.Then during network unbalance,a modifiedDFIG DPC model in the SVO positive dqandnegative dqreference frames is developed.Based onthe developed model,a system control strategy isproposed by eliminating the stator output activepower oscillations under unbalanced network conditions.Finally,simulation results on a 2-MW DFIGwind generation system are presented to demonstratethe correctness and feasibility of the proposed controlstrategy.
SIMULATION STUDIES,Simulations of the proposed DPC strategy for aDFIG-based wind power generation system wereconducted using PSCAD/EMTDC.
A single-phase load at the primary side of the coupling transformer was used to generate the voltageunbalance.The nominal DC link voltage was set at1 200 V and the switching frequencies for both converters were 2 000 Hz.The main target of the grid sideconverter was assigned to control the DC link voltagewith the similar method used in(Song and Nam,1999;Hu et al.,2007).As shown in Fig.7,a high frequencyAC filter is shunt-connected to the stator side to absorb the switching harmonics generated by the two
converters.Initial studies with various active and reactivepower steps were carried out to test the dynamic response using the conventional control scheme shownin 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
largeinertia of the wind turbine resulting in a slow changeof the rotor speed.The activeand reactive powers were initially set at 0 MW and0.5 MV·A,respectively,whererefers to absorbing reactive power.Various power steps were applied,viz.,active and reactive power references werechanged from 0 to2 MW at the instant of 1.3 s.
CONCLUSION，This paper has proposed an analysis and an improved DPC design for    a DFIG-based wind powergeneration system during network voltage unbalance.Simulation results were presented to demonstrate thefeasibility of the proposed control scheme.Conclusions can be drawn as follows:(1)The conventional DPC scheme without net-work unbalance considered can provide pretty gooddynamic system performance when the supplyvoltage is strictly balanced.However,once the net-work is slightly unbalanced,the performance deteriorates with high stator/rotor current unbalances andsignificant oscillations in the stator active/reactivepower and electromagnetic torque.(2)The proposed DPC scheme,which is implemented in the SVO positive dq+ and negative dqreference frame
s,gets rid of the decompositionprocess of positive and negative sequence rotor currents in the vector control scheme using dual-PI rotorenhanced by the elimination of the stator output activepower oscillations and the reduction of the electro-magnetic torque pulsations during network unbalance.
附录B 中文参考文献
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
风力发电场的双馈感应发电机与转换器在25％〜30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。
reactive翻译
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，它是实施积极的伺服机构+和消极的参考框架，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。

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