【作者】 陈晨；

【导师】 王海风；

【作者基本信息】 华北电力大学(北京) ， 电力系统及其自动化， 2019， 博士

【摘要】 近年来,在实际电力系统中发生了多起由并网双馈风电机组(doubly fed induction generator,DFIG)风电场引发的次同步振荡事故,严重威胁了电力系统的安全、稳定运行。对于含并网DFIG风电场的串补输电系统,研究表明并网DFIG风电场引发次同步振荡的机理是换流器控制系统参与的感应发电机效应,串联补偿电容器是次同步振荡产生的重要因素。然而,在2015年7月1日我国西部哈密地区电力系统发生了由并网风电场引发的严重次同步振荡事故,该起事故所涉及区域内的输电线路没有安设串联补偿电容器,并且事故导致了 300公里外三台大型火电机组发生次同步扭振而相继切机。目前,并网风电场引发无串补电力系统次同步振荡的机理尚不明确。为此,本文从模式谐振的角度,围绕并网DFIG风电场引发无串补电力系统次同步振荡机理展开深入研究,主要研究内容和成果包括:(1)基于开环模式谐振理论,研究了并网DFIG风电场引发无串补电力系统次同步扭振和次同步控制相互作用的机理。通过将并网DFIG风电场作为反馈通道,电力系统其余部分作为前向通道,构建了适用于次同步振荡稳定性分析的含并网DFIG风电场电力系统的单输入单输出闭环互联模型。基于所构建的模型,分析了并网DFIG风电场引入的动态交互作用对电力系统次同步振荡稳定性的影响,该影响可以通过开、闭环次同步振荡模式之间差值进行评估。开环模式谐振条件下,并网DFIG风电场与电力系统其余部分之间存在强动态交互作用,这种强动态交互作用使得相应的闭环次同步振荡模式在复平面上分布于开环次同步振荡模式两侧相对的位置,削弱电力系统的次同步振荡稳定性。研究表明,当换流器控制系统参数整定不当时,DFIG风电场与电力系统其余部分中同步发电机之间的开环模式谐振可能会使得同步发电机的闭环轴系扭振模式位于复平面的右半平面,进而引发电力系统次同步扭振。DFIG风电场之间的开环模式谐振可能会使得与换流器控制系统相关的闭环次同步振荡模式的模式阻尼变负,引发电力系统次同步控制相互作用。(2)研究了近似强开环模式谐振条件下并网DFIG风电场引发无串补电力系统次同步振荡机理。构建了含并网DFIG风电场电力系统的多输入多输出闭环互联模型,基于此模型论证了开环模式谐振和近似强模式谐振是相同的模式条件,即开环模式谐振是近似强模式谐振的一类特殊情况,并定义为近似强开环模式谐振。基于状态空间矩阵的特征值灵敏度理论,提出了一种分析近似强开环模式谐振条件下并网DFIG风电场引发电力系统次同步振荡的方法。所提方法通过将开环子系统之间的动态交互作用与闭环互联系统的次同步振荡稳定性相联系,明确了近似强模式谐振的物理意义是并网DFIG风电场引入的动态交互作用。另外,所提方法的理论基础是状态空间矩阵的特征值灵敏度理论,为基于开环模式谐振理论的并网DFIG风电场引发电力系统次同步振荡研究工作提供了严谨的理论基础,将开环模式分析方法的适用性拓展至多输入多输出闭环互联模型。(3)研究了多模式谐振条件下并网DFIG风电场内部风电机群间动态交互作用引发无串补电力系统次同步振荡机理。构建了并网DFIG风电场含多风电机群时电力系统的线性化状态空间模型。基于所构建的模型,提出多模式谐振理论,研究了并网DFIG风电场内部风电机群间动态交互作用对电力系统次同步振荡稳定性的影响。研究表明,当并网DFIG风电场内部N个风电机群的开环次同步振荡模式在复平面上相互接近时会发生多模式谐振,导致相应的N-1个固定闭环次同步振荡模式和一个变化闭环次同步振荡模式分布在开环模式谐振点两侧相对的位置,削弱电力系统的次同步振荡稳定性。基于多模式谐振理论,研究了次同步振荡的“频率漂移”现象。当电力系统中发生由并网DFIG风电场内部风电机群间多模式谐振引发的次同步振荡时,随着投运风电机群数量的不同,变化闭环次同步振荡模式的频率也会随之改变,若该振荡模式为电力系统的主导次同步振荡模式,次同步振荡会随着投运风电机群数量的不同而发生“频率漂移”现象。更多还原

【Abstract】 In recent years,several sub-synchronous oscillation(SSO)incidents caused by grid-connected doubly-fed induction generator(DFIG)wind farms occur in practical power systems.The SSO incidents seriously threaten the safe and reliable operation of power systems.For the series-compensated transmission systems with grid-connected DFIG wind farms,an extensive study has reached the well-accepted conclusion that the mechanism of SSOs caused by grid-connected DFIG wind farms can be attributed to the induction generator effect participated by the converter control system.In addition,the series compensation capacitor is a vital factor.However,on July 1st 2015,a serious SSO incident caused by grid-connected wind farms occurred in the Hami power system in West China where there are no series compensated transmission lines.During the incident,torsional stress relays of three large-scale thermal generation units in a power plant,which was 300 km away,were triggered and the units were tripped-off due to the torsional oscillations.Presently,the mechanism of SSOs caused by grid-connected wind farms in power systems without series compensated lines is not clear.Therefore,this dissertation investigates the mechanism of SSOs caused by grid-connected DFIG wind farms in power systems without series compensated lines from the perspective of modal resonance.The research works of this dissertation are listed as follows.(1)Based on the open-loop modal resonance theory,the mechanisms of sub-synchronous torsional oscillations(SSTOs)and sub-synchronous control interactions(SSCIs)caused by grid-connected DFIG wind farms in power systems without series compensated lines are investigated.By taking the grid-connected DFIG wind farm as the feedback loop and the rest of the power system as the forward loop,the single-input single-output closed-loop interconnected model of the power system with grid-connected DFIG wind farms is established which is applicable to the SSO stability analysis.Based on the established model,the impact of the dynamic interactions induced by the grid-connected DFIG wind farm on the SSO stability of the power system is examined.The impact can be evaluated by the difference between open-loop SSO modes and closed-loop SSO modes.Under the condition of open-loop modal resonance,strong dynamic interactions between the grid-connected DFIG wind farm and the rest of the power system are exhibited.Due to the strong dynamic interactions,the corresponding closed-loop SSO modes are located in the opposite positions with respect to those of open-loop SSO modes on the complex plane.As a consequence,the SSO stability of the power system is deteriorated.The study indicates that,when the parameters of the converter control system are inappropriately tuned,the open-loop modal resonance may occur between the DFIG wind farm and the synchronous generator(SG)in the rest of the power system.Due to the open-loop modal resonance,the closed-loop shaft torsional mode of the SG can be located on the right half plane which will cause SSTOs in the power system.In addition,as a result of the open-loop modal resonance between two DFIG wind farms,the modal damping of the closed-loop SSO mode corresponding to the converter control system can become negative which will cause SSCIs in the power system.(2)The mechanism of SSOs caused by grid-connected DFIG wind farms in power systems without series compensated lines under the condition of near strong open-loop modal resonance is investigated.The multi-input multi-output closed-loop interconnected model of the power system with grid-connected DFIG wind farms is firstly established.Based on the established model,it is demonstrated that the open-loop modal resonance and near strong modal resonance are the same modal condition.In specific,the open-loop modal resonance is a special case of near strong modal resonance which is defined as the near strong open-loop modal resonance.Based on the eigenvalue sensitivity theory of the state-space matrix,an analysis method is proposed for the examination of SSOs caused by grid-connected DFIG wind farms in power systems under the condition of near strong open-loop modal resonance.The proposed method connects the SSO stability of the closed-loop interconnected system to the dynamic interactions between open-loop subsystems in which way the physical significance of the near strong modal resonance is clarified,i.e.the dynamic interactions induced by the grid-connected DFIG wind farm.Moreover,as the proposed method is based on the eigenvalue sensitivity theory of the state-space matrix,the method provides a rigorous theoretical basis for the open-loop modal resonance theory based research works on SSOs caused by grid-connected DFIG wind farms in power systems.Furthermore,the applicability of the open-loop modal analysis method is extended to the multi-input multi-output closed-loop interconnected system.(3)The mechanism of SSOs caused by dynamic interactions among wind clusters within the grid-connected DFIG wind farm in power systems without series compensated lines under the condition of multi-modal resonance is investigated.The linearized state-space model of the power system with the grid-connected DFIG wind farm which consists of multiple wind clustsers is established.Based on the established model,the multi-modal resonance theory is proposed to evaluate the impact of dynamic interactions among wind clusters within the grid-connected DFIG wind farm on the SSO stability of the power system.The study shows that multi-modal resonance will occur when open-loop SSO modes of N wind clusters are close to each other on the complex plane.In consequence,the corresponding N-1 fixed closed-loop SSO modes and one varied closed-loop SSO mode will be located approximately in the opposite positions with respect to the multi-modal resonance point where the SSO stability of the power system is deteriorated.In addition,the frequency drift of SSOs is examined based on the proposed multi-modal resonance theory.When the SSO caused by multi-modal resonance among wind clusters within the grid-connected DFIG wind farm occurs in the power system,the oscillation frequency of the varied closed-loop SSO mode will be changed with respect to the number of in service wind clusters.Therefore,if the varied closed-loop SSO mode is the dominant SSO mode of the power system,the frequency drift of the SSO will occur when the number of in service wind clusters is different.更多还原