【作者】 廖国栋；

【导师】 王晓茹；

【作者基本信息】 西南交通大学 ， 电力系统及其自动化， 2009， 博士

【摘要】 近年来,国外发生了多起因为电压失稳导致的大规模停电事故,造成了巨大经济损失,严重影响了社会生活。电压稳定事故一般具有突发性和隐蔽性的特点,一旦发生电压崩溃就很难挽回,但现有的电压稳定评估方法尚难以满足在线实时分析的需要。基于局部指标的电压稳定评估方法仅利用相关测量信息进行电压稳定评估,降低了网络解算量,具有有利于在线实时应用的优点。因此,研究适合在线应用的电压稳定性局部指标及基于局部指标的电压稳定性在线监测理论与方法,为电网在线监测、预防和校正控制提供新的理论手段,对电力系统避免恶性电压崩溃事故的发生,具有重要的理论与实用意义。论文主要以电力系统电压稳定性局部指标及其应用为主要研究内容,重点研究了电力系统戴维南等值参数辨识、性能良好的局部指标建立以及局部指标在多机系统中拓展问题,发展了基于局部指标的电力系统电压稳定评估方法,对基于测量的局部指标法能真正应用于电力系统电压稳定性在线实时评估具有重要的促进作用。论文通过在观测模型和动态模型中引入不确定性,建立了电力系统戴维南等值系统的离散时间不确定模型,并进一步以此为基础,融合预报协方差矩阵的自适应调整和状态空间鲁棒性估计,提出利用自适应鲁棒卡尔曼滤波算法辨识戴维南等值参数。该模型和算法计及了系统运行方式变化、故障扰动及非线性负荷动态行为等因素对电力系统节点戴维南等值参数的影响,算法有强的抗干扰能力和跟踪能力。此外,还将基于UDU~T分解的测量更新时间更新技术应用到戴维南等值参数辨识中,解决了计算机舍入误差导致滤波发散的问题,使得戴维南等值参数辨识有良好的数值稳定性。针对现有的电压稳定性局部指标应用于电压稳定在线监测时都存在一定局限的不足,论文基于简单的单电源功率传输系统模型,通过引入反映工作点区域位置的符号函数,提出了一种新的节点负荷裕度指标,它可准确地反映节点的稳定负荷裕度,能给出运行点是否位于系统P-V曲线上半支或下半支的信息,指标具有良好的准线性特性,且在分岔点附近对小的负荷变化不敏感。另外,论文利用反映无功功率裕度的节点负荷裕度指标辨识电压不稳定无功薄弱区域,得到了与模态分析法相一致的结论。为了将如上述节点负荷裕度指标拓展到多机系统,论文提出了两种计算单电源功率传输等值系统的方法。第一种方法仅根据一个系统状态的测量相量,直接计算单电源功率传输等值系统参数,其等值负荷仅受被监测点相邻区域内相关母线节点负荷的影响。该方法与L指标法相比,减小了转移负荷的影响,提高了指标值精度,且也能应用于不含负荷的联络母线。第二种方法在第一种方法的基础上,减小需要信息的范围,它仅根据被监测点相邻区域内的信息计算单电源功率传输等值系统参数,但利用多个系统状态的电压电流相量,采用上述的自适应鲁棒卡尔曼滤波估计区域外电网等对指标值的影响。辨识时,把根据区域电网计算得到的等值系统参数设置滤波初值,并通过预估的参数值范围及节点电压变化信息,剔除无效的估计值。第二种方法提高了持续激励条件难以满足条件下指标值的精度,且能应用于不含负荷的联络母线,发展了基于戴维南等值定理将电压稳定性局部指标拓展多机系统中的方法。电力系统负荷一般具有随电压变化而变化的特性,论文考虑到负荷电压特性对电压稳定性有影响的实际情况,通过引入单电源功率传输系统达到鞍结分岔点时的特征方程,提出了一种准确计及负荷电压特性的电压稳定性局部指标。该指标舍弃了根据方程实根解的存在条件和雅克比矩阵行列式建立计及负荷电压特性的电压稳定性局部指标的方法,准确地反映了负荷电压特性对系统电压稳定性的影响。对于求解局部指标时遇到的非线性方程组,应用NLEQ-RES(global Newton method with residual based convergence criterionand adaptive trust region strategy)算法求解,以改善数值计算的收敛性及其收敛速度。更多还原

【Abstract】 In recent years, several foreign large-scale blackouts induced by voltage instability happened, which caused great economical losses and serious sed-effects on people’s lives. Voltage instability presented the features of sudden and concealment. Once it happens, it is difficult for power system to survive, whereas the existing voltage stability assessment methods still cannot meet the requirements of real-time analysis. Nevertheless, the assessment method based on voltage stability index is beneficial to on-line real-time application, which just used the relevant measurements and had lower calculation complexity for the network solution. Therefore, it has important theorical and practical significance to study the voltage stability index and the assessment method based on voltage stability index, which provide a new thoerical means for on-line monitoring, preventive and corrective control to avoid voltage collapse in power systems. In this thesis, power system voltage stability local index and its application were focused on, and the issues related to the Thevenin equivalent parameters identification in power systems, the construction of local index of good performance and the application of local index in multi-machine systems were mainly studied, which further developed the voltage stability assessment method based on local index, and contributed a lot to the progress of the realistic application of measure-based local index in the voltage stability real-time assessment of power system.By adding uncertainty to the dynamic model and measurement model, the state-space description of Thevenin equivalent systems with uncertain models was defined. Based on the defined model, altogether with the robust estimation in the state-space and the adaptive modification of prediction covariance matrix, a new algorithm called adaptive robust kalman filter was proposed to track Thevenin equivalent parameters. The uncertain models considers the effects of time-varying factors as operation models, disturbances and nonlinear loads on Thevenin equivalent parameters in power systems, and the new algorithm has good robustness and powerful capabilities of anti-jamming. Otherwise, to solve the problem of divergence of Thevenin equivalent parameters identification caused by the round-off errors in the computer, the measurement updating andtime updating using the UDU~T factorization were used, which guarantee that the filtering has favorable numerical stability.Based on a single source power system, a node load margin index for on-line monitoring voltage stability was proposed to overcome the limitations of existing voltage stability indices, in which a sign function was used to reflect the operation segment. Not only the load margin at a bus, but also the position of operating point--the upper or lower half segment of P-V curve-can be reflected accurately by the proposed index, which also has the characteristic of prelinearity and is insensitive to small load variations in the vicinity of the bifurcation point. Besides, it was found that the voltage instability region sensitive to the reactive power support identified with the reactive load margin index is the same as the one with modal analysis method.To extend the voltage stability index as the above-mentioned load margin index to the multi-machine system, two methods were proposed to compute the equivalent single source system respectively. The first one directly use measured phasors at one operation state to compute the equivalent single source system, in which the equivalent load only included the effects of relevant loads in the surrounding. Compared with L index, this expression reduced the sed-effects of transferred load with improving the index accuracy of voltage stability index, and could also be used to monitor tie buses. Based on the first one, the second only used the information from the surrounding power grids of the monitored bus to compute an equivalent single source system, and the effects of the other parts as the external grids were identified with the information at several operation states by the proposed adaptive robust Kalman filter. Its initial guesses were set to be the computed equivalent system parameters, and the invalid estimated values were filtered out by the estimated scopes of parameters and the voltage magnitude changes at the monitored bus. This approach improves the index accuracy when persistent excitation condition is not met, and can be used to monitor tie buses, and thus further develops the method of extending the voltage stability index to the multi-machine system by Thevenin theorem.In power systems, the load at bus often varied with the change of the bus voltage. Considering the fact that load characteristics affected the voltage stability, by introducing the characteristic equation of saddle bifurcation in a single source power system, an index taking the static load characteristics into account was presented. This approach discarded the method of establishing voltage-stability index by the real-root existing conditions of equations or the determinant of Jacobin matrix and the proposed index accurately reflected the influences of static load characteristics on voltage stability. While computing the local index, NLEQ-RES (global Newton method with residual based convergence criterion and adaptive trust region strategy) was applied to improve good convergence rate and global convergence property for the nonlinear equations.更多还原