1、 毕业设计（外文翻译） 题 目 在电网电压不平衡条件下的动态建模和风力涡轮机的直接功率控制 系 （院） 自动化系 专 业 电气工程与自动化 学生姓名 学 号 2007090124 指导教师 职 称 2011 年 3 月 8 日 1 Dynamic modeling and direct power control of wind turbine driven DFIG under unbalanced network voltage condition Abstract:This paper proposes an analysis and a direct power control(DPC
2、)design of a wind turbine driven doubly-fed induction generator(DFIG)under unbalanced network voltage conditions.A DFIG model described in the positive and negativesynchronous reference frames is presented.Variations of the stator output active and reactive powers are fully deduced in thepresence of
3、 negative sequence supply voltage and rotor flux.An enhanced DPC scheme is proposed to eliminate stator activepower oscillation during network unbalance.The proposed control scheme removes rotor current regulators and the decompositionprocessing of positive and negative sequence rotor currents.Simul
4、ation results using PSCAD/EMTDC are presented on a 2-MWDFIG wind power generation system to validate the feasibility of the proposed control scheme under balanced and unbalancednetwork conditions. Key words:Doubly-fed induction generator(DFIG)Windturbine,Direct power control(DPC),Stator voltage orie
5、nted(SVO),Unbalanced network 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 of25%are becoming increasinglypopular.Compared with the wind turbines using fixedspeed induction generato
6、rs 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 di
7、stribution networks couldusually have small 滨州学院本科毕业设计 (外文翻译 ) 2 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 currentscrea
8、te 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
9、 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).The schemein(Jang et al.,2006；Zhou et al.,2007；Xu and Wang,2007；Hu et al.,2007)emplo
10、ys 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 approa
11、ch 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),
12、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(DT
13、C)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
14、 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
