【作者】 张宁；

【导师】 刘玉田；

【作者基本信息】 山东大学 ， 电力系统及其自动化， 2008， 博士

【摘要】 我国经济发展与能源资源分布的不平衡性,决定了我国应建设更高电压等级电网以实现能源资源在全国范围内的优化配置,也决定了西北、西南等大型能源基地电力大规模、远距离外送是我国电网未来一段时期发展的重要任务。随着我国能源基地和特高压电网的建设,将形成华东、东北、华中、粤闽琼和京津冀鲁五大受端电网。保证大受端电网安全稳定运行是一项非常具有挑战性的任务,需要从系统规划建设、运行方式分析、调度管理和实时控制等多个方面进行深入研究。其中,互联系统输电能力的确定在电力系统安全运行中起着重要作用,过于保守的计算结果将限制电网资源充分发挥效益;反之,过于冒进的计算结果可能导致系统控制措施不当,在预想事故发生后失去稳定。深入分析影响输电能力计算结果的各种因素及其影响规律,准确地确定互联系统的最大输电能力,并从电网运行与受端电压控制等角度出发研究提高输电能力的各种措施,是迫切需要解决的问题,具有重要的理论价值和实际意义。在广泛阅读、分析和总结相关文献资料基础上,本文从电力系统数值仿真有效性、特高压/超高压电磁环网对安全稳定性的影响以及静止同步无功补偿作用等方面,运用数值分析、人工智能和自定义建模等理论和技术,密切结合我国电网实际和发展规划,对如何提高特高压电网输电能力进行了深入研究,主要研究工作和取得的创新性成果如下所述。针对输电能力仿真评估中数值仿真有效性问题,基于各层面评估需求,提出了五个仿真有效性量化评价指标,初步建立了电力系统数值仿真有效性评价体系,并应用于实际电网仿真分析。五个仿真偏差评价指标包括:(1)基于轨迹的稳定性仿真偏差评价指标,利用机组间最大功角差来从宏观层面评估仿真偏差大小和趋势;(2)基于扩展等面积准则的稳定性仿真偏差评价指标,利用EEAC提供的暂态功角稳定裕度指标从宏观层面评估仿真偏差大小和趋势;(3)仿真偏差极值评价指标,利用所有同类型物理量在整个仿真时间窗内仿真偏差的最大值反映仿真偏差的大小;(4)仿真偏差均值评价指标,利用所有同类型物理量在整个仿真时间窗内仿真偏差在时间轴上的平均值来反映仿真偏差的大小;(5)仿真时效比指标,利用模型等因素造成的仿真耗时变化和仿真偏差的比值来评价由于模型、数值方法及参数因素对仿真计算代价(在此指仿真计算耗时)的影响。结合福建电网实际数据,利用上述指标详细研究了发电机模型、负荷模型以及积分步长对仿真有效性的影响。分析计算中发现,模型因素可能导致单一变量的仿真偏差很大,但如果系统中所有该同类变量的偏差变化趋势一致,则可能对系统宏观属性(如暂态稳定性)的影响相对很小。指出对于电力系统而言,仅仅孤立地通过不同场景下单一变量的仿真偏差来评估仿真有效性是不充分、不恰当的,需要从系统层面评估模型等因素对仿真有效性的影响。实际电网的仿真计算结果表明,所建立的评价指标能够从不同侧面来量化评估数值仿真有效性,所建立的仿真有效性评价体系有效、实用。发电机模型、负荷模型和积分步长等仿真计算因素会影响暂态稳定计算结果,从而也必然影响考虑暂态稳定约束时最大输电能力的计算。分别针对单机系统、山东电网和华北—华中—华东特高压同步互联电网,详细计算分析了发电机模型、负荷模型和积分步长等因素对输电能力计算结果的影响。计算分析表明,发电机模型对输电能力计算结果的影响明显,不同系统下发电机模型对输电能力计算结果的影响程度不等;在绝大多数情况下,详细模型得到的计算结果偏小,二阶模型下计算结果偏大;相同系统在不同故障约束下,发电机模型对输电能力计算结果的影响程度也不同;从实例仿真计算结果来看,发电机模型导致的最大偏差超过18%,不容忽视。负荷模型的选取对电网输电能力计算结果影响也较大,通常恒阻抗负荷模型更有利于系统稳定,计算得到的输电能力更大,但对于单机系统影响趋势却相反;实际电网计算中,不同负荷模型下输电能力计算结果相差最大超过25%。相对发电机、负荷模型而言,积分步长对输电能力计算结果的影响较小,且与发电机模型等其他因素密切相关,通常次暂态模型下积分步长的影响较大;大积分步长下计算结果往往偏小;对于实际系统,积分步长对输电能力的影响都较小,计算偏差通常小于1.5%,实际计算中可忽略不计。总之,模型等因素对输电能力计算结果的影响较大,在输电能力计算、方式校核、控制策略制定等工作中,采用更加符合实际情况的模型非常重要。在实际输电能力仿真评估中,应做好模型调研工作,尽可能采用符合实际的模型和可靠的计算方法,以保证计算结果的有效性。高低压电磁环网运行方式可以在稳态情况下输送更多的功率,但也存在严重的安全隐患。是否开环运行,需要正确分析不同方案对电网安全性、稳定性和运行经济性等方面的影响,以综合利弊。基于特高压-超高压电磁环网的特点,提出了一种1000kV/500kV电磁环网模糊综合评价方法,基于层次分析法建立了开环方案模糊综合评价模型,建立了由目标层、准则层和指标层构成的评价指标体系。准则层由静态安全性、暂态稳定性和运行经济性三个层面构成,每个层面又各包含两个行为指标:(1)静态安全性层面,以线路/变压器过载和节点电压越限两个行为指标来反映系统静态安全水平;(2)暂态稳定性层面,以机组间最大功角差和断面输送极限两个行为指标来反映系统暂态稳定性水平;(3)运行经济性层面,以短路电流(决定了开关设备投资)和系统网损两个行为指标来反映系统运行经济性。确定了隶属度函数以及评语集,基于模糊综合评价方法对上述指标进行了模糊评价和综合。首先对所有候选开环方案的静态安全性、暂态稳定性和运行经济性进行计算与分析,然后对各方案得到的数据进行分析评价,主要进行评价指标权重计算、模糊评价指标计算与模糊化、模糊综合评价和评价结果的输出等。在Windows环境下编制了电磁环网开环方案模糊综合评价程序。该程序与电力系统分析综合程序(PSASP)相配合,可自动读取PSASP计算结果并依据所定义指标对运行方案进行模糊综合评价。提出的模糊综合评价方法综合考虑了电网的静态安全性、暂态稳定性和运行经济性,可对电磁环网开环方案作出定量、全面、综合的评价。该方法不仅可以包含专家经验和知识,而且将定性分析与定量计算相结合,能为规划人员提供科学决策依据。针对华北—华中—华东特高压交流同步电网中的1000kV-500kV电磁环网进行了深入分析,计算了各种行为指标以及运行方式优先度指标,所得电磁环网开环方案的模糊综合评价结果与规划人员的实际分析和判断相一致,表明所提出的高低压电磁环网开环方案的模糊综合评价方法是可行的,具有实际应用价值。静止同步补偿器具有无功调节范围宽、调节速度快的特点,可用于提高受端电网电压支撑能力和电压稳定性,从而间接提高特高压电网的输电能力。在深入分析和总结STATCOM稳态和动态数学特性基础上,建立了基于功率注入法的STATCOM稳态模型和基于受控电流源的STATCOM动态模型,并在PSASP环境下通过用户自定义功能实现了这些模型。实例计算中发现,STATCOM模型参数中放大倍数K的取值会影响潮流计算的收敛特性,K过大或过小都会导致迭代次数增加。以山东电网为例对STATCOM动、稳态调压特性进行了详细分析,仿真结果表明建立的模型实用有效,STATCOM可以起到较好的动态电压支撑、强补无功和抑制电压跌落的综合效果。结合特高压接入山东电网运行的实际需要,从提高受端电压支撑能力角度研究了STATCOM对输电能力的影响,采用基于功率传输路径的电压稳定性评估方法,分析了STATCOM的作用。仿真结果表明,STATCOM能有效提高系统的动态稳定性,提高电压稳定性的效果明显。基于根据功率传输路径理论定义的局部稳定指标,确定了基本负荷水平下电网中电压稳定薄弱节点,分析了山东电网电压稳定薄弱区域,优选了STATCOM安装地点。结合电源和电网建设,可优先考虑在崂山站装设STATCOM,以便提高山东电网东送通道的功率极限和山东电网的受电能力,从而有利于提高特高压系统对山东电网的电力输送。更多还原

【Abstract】 The unbalance between economic development and energy distribution of China determines that it is necessary to build ultra-high voltage(UHV) power grids to optimally allocate energy resource across the whole country, also determines that the main task of state power grids of China is to transfer large-scale power from the Northwest and Southwest energy bases to receiving-end systems for a long time. With the development of energy bases and UHV, several huge receiving-end power systems are emerging. To ensure the security operation of such receiving-end systems is a challenging work, lots of works should be done on system planning, operation, dispatch management and realtime control decision. Finding out the exact total transfer capability(TTC) of interconnected power systems plays an important role in power system security operation and control. Conservative results will limit the full use of available resources of power grids. In contrast, too progressive results may lead to improper control measures, even lost stability when anticipated fault occurs. Analysing these various factors and their affects on TTC calculation, determining the accurate TTC of interconnected power system, and studying how to improve TTC by operation plan optimization and voltage control, are urgent and have theoretical and practical significance.Based on wide reading, analizing and summarizing, intensive studies are done on how to improve the UHV’s TTC. Considering China’s power grids actual planning and development, the validity of numerical simulation, the effects of UHV/EHV electromagnetic loop network on security operation and the application of static synchronous compensator(STATCOM) are investigated. Some key works and creative results are listed in the following:According to the issues of validity of numerical simulation when calculating TTC, Based on the various assessment demands, five indicators are proposed to assess the validity of numerical simulation, the validy assessement scheme is established. The five indicators include: (1) the stability deviation assessment indicator based on generator angle trajectory, which can quantitatively evaluate the deviations caused by various simulation facts by the maximum angle difference in the system; (2) the stability error assessment indicator based on the Extended Equal Area Criterion(EEAC), which can quantitatively evaluate the errors caused by numerical simulation from the macroscopic view using the stability margin provided by EEAC; (3) the extreme deviations evaluation indicator, which reflects the maximum deviation during the simulation time window; (4) the average deviation evaluation indicator, which calculates the average deviation within the entire simulation time window; (5) the cost-effective indicator, which can evaluate the effects of models, numerical methods and parameters on the cost of numerical simulation - consumed time. Based on the five proposed indicators, detail works are done with Fujian power system to study the impacts of generator models, load models and integral-step size on numerical simulation deviations. Results show that generator and load modeling may cause apparent deviation in simulation results, and these indexes can evaluate the validity of numerical simulation from different aspects. It’s also found that when the deviations tendencies are the same, the effects on system properities, such as transient stability, may be very slight even if the effects on single variable are apparent. It is indicated that, according to power system, it is not sufficient and suitable to assess the simulation validty by only assessing the deviations of single variable. The assessment from system viewpoint is necessary. The results of detail analysis show that the proposed indicators and assessment scheme works well.The factors such as generator modeling, load modeling and integral-step size may bring simulation deviations to transient stability calculation. Therefore, they may also affect the results of TTC calculation when transient stability treated as constraint conditions. Respective works are done with one-machine system, Shandong power system and North-Central-East China interconnected UHV synchronous power system to analyzs the effects of modeling and parameter issues on TTC calculation. Analysis shows that generator models may bring apparent deviation to TTC calculation. Usually, the TTC got with second-order and transient generator models are larger than that with sub-transient generator models, and the deviations caused by generator modeling varies with different power systems and different faults. The maximum deviation caused by generator model is more than 18% in the studying cases, which can’t be ignored. Load modeling also may influence the results of TTC calculation. Usually, constant impendance load model contributes more to transient stability than constant power load model, so the TTC calculated with constant impendance load model is bigger than that with constant power load model. The maximum deviation caused by different load models exceed 25 %. However, the results show that the effects of load model on simulation result varies according to different power system, the trend of deviation varing may be contrary according to different system. Integral-step size is another issue that can affect numerical simulation. Compared with the impacts caused by generator model and load model, the impacts caused by integral-step size are very small, and closely related to generator model. According to one-machine system, the effects are more apparently when sub-transient generator models used, but it almost has no impact when second-order generator model adopted. According to practical power systems, the impact of integral-step is much smaller than that of generator model and load model. Usually, the deviations are almost all less than 1.5%, which can be ignored in practice. In short, models and other factors may bring apparent deviations when calculating TTC, it’s very important to choose proper models when performing power system numerical simulation and analysis. Therefore, models and parameters should be used carefully in TTC calculation and decision making to ensure the validity of numerical simulation.In steady state, more power can be transfered when the system is operating with the high-low-voltage electromagnetic loops closed, but serious potential safety issues may also exist. To open the electromagnetic loops or not depends on many factors, such as security issues, stability issues and economic issues. These factors must be detailedly assessed when related decisions making. Based on the characteristics of UHV-EHV power system, a fuzzy evaluating method of lOOOkV-500kV electromagnetic loop is presented. Based on analytic hierarchy process (AHP), the corresponding fuzzy comprehensive evaluation model is established, and its indicator system is defined. The static security indicators, including branch overloading and node voltage off-limit information, are used to reveal system static security. The transient stability indicators, including the maximum generator angle difference between any two machines and the transfer limit of selected cross-sections, are used to assess system transient stability. The operation economic indicators, including the changes in investment because of the increase of short circuit current and system total losses, are used to reflect system economic situation. The member-ship functions and the comment set are determinded. Based on fuzzy comprehensive evaluating method, the indicators are evaluated. Firstly, performing numerical simulation to calculate static security, transient stability and the economy of operation, and then calculate these proposed indicators. Finally, the method gives a quantitative and comprehensive evaluation of the electromagnetic loop opening schemes based on these indicators.A program is developed under Windows platform to do the presented fuzzy comprehensive evaluation of electromagnetic loop opening schemes. Working together with the Power System Analysis Software Package(PSASP), it reads the simulation results provided by PSASP, calculates the indicators, then analyse and perform fuzzy evaluation, which mainly includes fuzzy treating of indicators, comprehensive fuzzy evaluating of all the indicators, and outputs the evaluation results. The method is applied to North-Central-East China interconnected UHV synchronous power system. The results compliance well with practical experience, which verifies the validity of the presented method, and it will help a lot in the operation of UHV/EHV systems.STATCOM has characteristics of wide regulating range and fast regulating speed, which can be used to enhance the voltage bearing ability and improve voltage stability of the receiving-end power system. Based on detail analysis and summary of STATCOM static and dynamic characteristics, the static model of STATCOM based on injection power and the dynamic model of STATCOM based on controlled current source are established. These models are also implemented with PSASP by user-define modeling method. It is found that the gain K of the STATCOM model affects the convergence characteristic of power flow computation. The parameter, K, leads to the iteration number increase when it is too large or too small. The dynamic and static characteristics of user-defined STATCOM are detailedly analysed with Shandong power system. Simulation results show that the user-defined STATCOM models are convenient and efficient, and show that STATCOM can play a combined role in dynamic voltage regulation, strong reactive power supply and voltage drop suppression. Combined with the need of interconnection of Shandong power system with UHV system, using STATCOM to enhance the voltage support ability of Shandong power system is studied. The stability indicator based on power transmission path is used to find the weak nodes of voltage stability. The weak regions of voltage stability in Shandong power system are analysed, and the STATCOM locations are determined. Considering the power plant and power network development plans, Laoshan Station is the priority location to install STATCOM, which can improve the power transfer limit of the power corridor in Shandong power system, and enhance the power receiving ability of Shandong power system, which can also improve the transfer capacity of UHV power lines when the are connected with Shandong power grids.更多还原