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
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)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 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.Simulation 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.reactive的翻译
Key words:Doubly-fed induction generator(DFIG)Windturbine,Direct power control(DPC),Stator voltage oriented(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 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
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滨州学院本科毕业设计(外文翻译)
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).The 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
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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 negliable.However,like a conventional DTC,DPC has the problem ofunfixed switching frequency,due to the significantinfluence of the active and reactive power variati ons,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.
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