【作者】 杜三恩；

【导师】 印永华； 李柏青； 马世英；

【作者基本信息】 中国电力科学研究院 ， 电力系统及其自动化， 2008， 硕士

【摘要】 电压稳定性问题是当今电力界普遍关注的问题,准确实时监测电网的电压稳定程度对电网的安全稳定运行具有重要意义。广域测量系统可以实时、同步地测量安装节点的电压相量、电流相量以及发电机内电势和励磁电流等信息,为电压稳定实时监测提供了新的思路。相量测量单元的布点是广域测量系统建设的基础性工作。本文在综述研究已有的布点方法的基础上提出了基于最小支配集和模态分析的相量测量单元布点方法,该方法先应用最小支配集算法求出所有最小支配集,然后结合模态分析结果确定最终布点方案。该布点方法在满足电网最小完全可观的条件下尽量直接测量关键机组和关键节点的信息。电压稳定监测关键要有一个良好的电压稳定指标。本文在综述研究了已有的基于广域测量系统的电压稳定监测方法的基础上,详细推导和分析了已有的多个电压稳定指标,然后提出了两个新型的电压稳定指标,通过对多个电压稳定指标的计算速度、准确度、线性性的比较,最终选取了本文所提出的线路潮流指标。该指标利用线路两端节点电压相量、线路潮流以及线路参数,快速评估电压稳定性。通过实验仿真验证了该指标具有良好的准确度和线性性。电压崩溃事故往往是由个别线路或节点引发,逐渐扩散至更大范围,因此只要对最薄弱线路或节点进行监测,保证其电压稳定程度在可接受的范围之内,那么就可以认为整个系统运行在电压稳定状态。本文提出的最弱线路集保存着电网中电压稳定性最弱的若干线路,每计算周期只需计算该集合中线路的电压稳定指标,同时,该集合中的线路会不断更新。这样既节约了计算时间,又能保证系统电压稳定得到实时监测。为了实时监测负荷裕度,本文提出了指标拟合方法。该方法利用电压稳定指标的良好线性性,通过对电压稳定指标历史数据的拟合处理,同时考虑到最新计算结果的更新,从而得到当前状态的负荷裕度。该方法不仅减弱了个别因素的影响,而且有效利用到了大量历史计算结果。最后以重庆电网2007年网架结构为例,验证了本文所提出的布点方法的有效性,仿真结果也显示本文所提出的电压稳定指标能够反映系统电压稳定程度。更多还原

【Abstract】 Voltage stability has already drawn common concern of power industry nowadays, and it’s very significant to gird’s security and stability to monitor voltage stability degree accurately and real-timely. Wide area measurement systems can real-timely and synchronously measure many signals of the nodes where the phasor measurement units are placed, such as voltage phasor, current phasor, internal potential and excitation current of synchronous generator, which presents a new idea for voltage stability real-time monitoring.The placement of phasor measurement units is a basic work for wide area measment systems. In this thesis, after summarizing and studying the existing phasor measurement unit placement methods, a new placement method based on minimum dominating set and modal analysis is proposed. All minimum dominating sets can be calculated, and then considering the modal analysis resultes, the final placement scheme is determined. As the result of this method, key-nodes and key-generators can be directly measured, satisfying grid’s minimum complete observability.A good voltage stability index is the key to voltage stability monitoring. Based on summarization and study exsiting voltage stability monitoring approaches in wide area measment systems, several voltage stability indices are derived and analyzed in detail. Then, two new voltage indices are proposed. Through comparing speed, accuracy, linearity of all indices mentioned here, a new index named line flow index is choosed. This index can be calculated and assesses voltage stability quickly just using voltage phasors of the line, power flow through the line, parameters of the line. The results of simulation show that this index has good characteristics of accuracy and linearity.Voltage collapses often start at some lines or nodes, and spread to larger area. If the weakest lines or nodes are monitored and kept in acceptable voltage stable degree, the whole grid will be in voltage stable state. The weakest lines set presented in this thesis keeps a number of lines with weakest voltage stability. In a calculation cycle, just the voltage stability indices of the lines in weakest lines set are calculated, meanwhile, the lines in weakest lines set are renewed. As a result, not only the cycle time of calculation becomes shorter, but also the voltage stability of system is monitored.In order to assessment load margin real-timely, a method called index fitting is proposed, which makes use of the index’s good linear characteristics, and fits historical indices to a line, at the same time, keeps historical indices constant renewal. In the fitted line, the distance between current state and critical state is load margin. This method not only reduces the influence of random factors on voltage stability assessment, but also makes use of the historical indices.Finally, taking Chongqing grid in 2007 for example, the result of case study indicates that the phasor measurement units placement method proposed in this thesis is valid, and the voltage stability index proposed in this thesis can reflect voltage stability degree of power system.更多还原