Efficient starting point of load-flow equations

Load flow is the solution of the static operating state of an electric power transmission system and is the most frequently computer-performed power system calculation.

In this paper, an initial linear solution of the load-flow equations is developed taking into consideration the decoupling principles, i.e. the active power depends on the voltage angle and the reactive power on the voltage magnitude.

This initial decoupled linear solution is utilized as the starting point for the solution of the load-flow equations using such numerical methods as the fast linear method, Newton's decoupled method and the Gauss—Seidel method. Its performance is compared with that of the flat starting point (V = 1.0 p.u., D = 0.0 radians). The test power systems used to test its performance are these of the standard 14, 30, 57 nodes IEEE test power systems.     

Load-flow solution by Newton-Richardson method and its adaptation to optimal load dispatch

A new load-flow solution technique based on the Newton-Richardson method is proposed, which is an attractive alternative for systems where the conventional Newton-Raphson method is preferred. The solution accuracy and the convergence rate are practically the same as in the Newton-Raphson method, while computing time is about half. It is also advantageous for optimum load-flow studies, since the Jacobian is easily available. The proposed technique has been tested for load flows on IEEE 14, 30 and 57 bus test systems and also on a heavily loaded 28 bus system. It is tested on an IEEE 30 bus system for optimal load flow.     

New contributions to load-flow studies by the method of reduction and restoration

This paper presents a method of conducting load-flow studies of power systems using the technique of network reduction and restoration. The method is found to provide solutions for well-conditioned and ill-conditioned power systems faster than any of the well-known methods with an accuracy comparable to that of the Newton-Raphson method.The essential features of the method are: (1) one cycle of network reduction and restoration is required for every delta iteration of the load-flow solution, (2) only P-V buses are considered for delta iterations, (3) the order of the Jacobian matrix is small, (4) the Jacobian and its inverse are computed only once and (5) delta iterations are completely avoided for the solution of systems having no P-V buses.     

电力系统预想事故快速分析

鉴于自适应化简等值算法的有效性，本文提出了一个电力系统预想事故快速分析的新算法，该逄法首先构成了包括断开支路在内的局部等值小网，然后利用快速前代和快速回代技术对等值小网进行ＡＣ潮流求解，通过对ＩＥＥＥ－５７节点试验系统和华东１５８节点系统的验算，证明该算法不但有令人满意的精度，而且有较理想的机时节约。     

基于REI等值的多区域无功优化并行计算(英文)

将REI等值技术应用于求解多区域电力系统的无功优化并行计算问题,对系统各个分区的外部网络进行REI等值化简,并对相角传递、等值网络初值计算、外层协调计算与REI等值网络修正等关键问题提出了具体的解决办法。并以此为基础建立了适合多区域无功优化的并行计算模式,通过采用Matlab并行计算平台实现无功优化并行计算,以IEEE 39节点和某695节点实际系统作为算例,通过与集中优化方法和基于Ward等值的多区域无功优化并行算法进行比较,对所提方法的有效性和优缺点进行了详细分析。     

Improving high-voltage transmission system adequacy under contingency by genetic algorithms

The paper presents a methodology which can be used to improve the static adequacy of high-voltage (HV) transmission systems under contingency. In this case the most suitable actions to be taken for bringing the power system back to acceptable operation conditions are identified by means of a power system management software. The proposed software combines a micro-genetic algorithm (μGA) optimization procedure with a load-flow program based on the fringing current correction (FCC) method. The foreseen control actions consist in transformer tap setting, insertion and/or regulation (if variable) of shunt reactor and capacitor banks, change of network configuration, power re-dispatching and load shedding. The performance of the proposed procedure is tested with respect to the main parameters both of electrical power systems and of genetic algorithms (GAs). An application to existing HV transmission systems is presented and discussed in order to evaluate its possible use in a System Control Center.     

一种基于ANN技术的预想事故自动选择方法

本文提出了一种基于人工神经元网络（ＡＮＮ）技术的预想事故自动选择方法，利用快速解耦潮流计算的迭代一次法（ＦＤＬＦ１）构造了分别对应于支路有功潮流越限的有功功率性能指标ＰＩｐ 和对应于节点电压模值和发电机无功出力越限的电压－ 无功性能指标ＰＩＶＱ。用ＢＰ算法训练多层感知型神经元网络以求得对应于不同运行状态和不同网络拓扑结构的性能指标。通过算例分析，并与其它经典方法的比较，本方法在计算精度和速度方面非常令人满意，而且具有较高的事故捕获率。     

Real-Time Decoupled Equivalent Models for Static Security Analysis

This paper presents some new decoupled external system equivalent models for use in system security evaluation. Three different models i.e., decoupled Tie-line power flow model, decoupled Boundary bus Impedance model and decoupled Impedance-Admittance model are developed based on P-? and Q-V relations of fast decoupled load-flow formulation. The structure component of the models are then identified by processing real time data using Kalman filtering technique. Then the operating components of the decoupled equivalents are obtained from two new approaches. The performance of the various models with regard to contingency analysis has been presented using simulated data on a 25 bus test system. Persistency analysis of different input-output data is given to determine apriori choice of models. Also the bias conditions are derived to ascertain the accuracy of the models.     

Second-order, 3-phase load flow

The load-flow solution of unbalanced polyphase power systems is obtained using the phase-coordinate technique in which only the 1st-order derivatives of load-flow equations in polar form are used. However, the use of this (1st-order, 3-phase) method is considerably limited because of the long solution time and large core-storage requirement. The present paper outlines an exact method for solving the load-flow problem of unbalanced electrical networks in which full Taylor series expansion of load-flow equations is used. The load-flow equations are expressed in cartesian coordinates. The method is three to five times faster than the 1st-order, 3-phase method but requires slightly more memory due to the cartesian coordiante formulation. The mathematical steps, a solution algorithm and pertinent results are provided for illustration.     

发输电互联等值系统风险评估的解析模型

为快速而精确得出发输电组合系统中区域元件参数变化后的系统风险指标,在发输电互联系统改进等值模型的基础上,推导出系统风险指标对区域元件参数变化的解析表达式,并提出系统风险评估的算法和流程。利用该解析表达式所得出的图表不但可直观反映元件各参数变化对系统风险指标的影响,还可为电力系统规划和效益评估提供指导意见。论文还以互联RBTS系统和IEEE-RTS96系统为例,通过故障重数对系统风险指标影响的定量化研究,解释和证明了高阶故障对大电力系统风险评估的重要性。     

Probabilistic load-flow computation using point estimate method

A new probabilistic load-flow solution algorithm based on an efficient point estimate method is proposed in this paper. It is assumed that the uncertainties of bus injections and line parameters can be estimated or measured. This paper shows how to estimate the corresponding uncertainty in the load-flow solution. The proposed method can be used directly with any existing deterministic load-flow program. For a system with m uncertain parameters, it uses 2m calculations of load flow to calculate the statistical moments of load-flow solution distributions by weighting the value of the solution evaluated at 2m locations. The moments are then used in the probability distribution fitting. Performance of the proposed method is verified and compared with those obtained from Monte Carlo simulation technique and combined simulation and analytical method using several IEEE test systems.     

可重构技术在电力系统实时计算中的应用

可重构计算技术是一类新兴的高性能计算技术。简述了可重构计算这一新的技术,并概述了可重构计算技术在电力系统潮流及暂态稳定性计算中的应用。可重构计算技术结合适当的计算方法,可以大大提高电力系统分析计算的效率,因而在现代大规模电力系统实时分析计算及控制中具有广泛的应用前景。     

在线暂态安全稳定评估的分类滚动故障筛选方法

为满足在线暂态安全稳定评估对计算时间的要求,提出了基于模式和裕度估算的在线暂态安全稳定故障筛选方法。分别基于上一轮在线暂态安全稳定评估结果中各个预想故障的暂态功角稳定、暂态电压跌落安全、暂态电压稳定和暂态频率偏移安全的裕度及模式信息,并结合各个故障安全稳定模式中相关元件的潮流变化和投/退等信息,估算出新一轮在线暂态安全稳定评估所对应的运行状态下各个故障的暂态安全稳定裕度,并确定其相应的安全稳定模式,从而筛选出本轮在线暂态安全稳定评估需详细计算的预想故障子集。通过对实际电网在线数据的仿真分析,验证了所述方法的有效性和实用性。     

基于能量函数法的电网脆弱性评估

传统确定性电力系统安全评估方法难以考虑电力系统的随机性,难以实时、定量和直观地提供电网安全健康状态的诊断信息。文章引入了电网脆弱性的概念,拓展了传统的电力系统安全性概念,并考虑预想事故发生的概率,采用暂态能量函数法从暂态安全角度定量评估了电力系统的脆弱性,给出了电力系统的脆弱性指标和阈值。算例分析结果表明该方法在保证安全分析结果正确性的同时节省了机时,验证了该方法的合理性与有效性。     

Starting algorithm and modification for Newton-Raphson load-flow method

A starting algorithm for the Newton-Raphson method of load-flow calculation is proposed. The algorithm provides good starting values for the system variables by defining two new functions, the coupling between which is weaker than the coupling between the normal active and reactive power mismatch functions. A modification to the Newton-Raphson method is also proposed that takes into account most of the 2nd-order terms that are normally neglected. Results of systems solved by the standard Newton-Raphson and other methods, and by the modified method with the new algorithm incorporated, demonstrate the advantages of the proposed algorithm and modification.     

基于网络分割的电力系统潮流分解协调计算

因现有计算模式的速度已无法满足现代大规模电力系统实时计算的要求,故引入对等计算(P2P)模式以提供低廉而充足的计算力。为此研究了网络计算环境下的电力系统潮流计算模型,结合基于支路切割的网络分割方法和基于注入电流的潮流模型,提出了基于网络分割的电力系统潮流分解协调算法,将大规模互联电力系统分解成若干子网络,子网络间只需交换边界母线的电压状态就可完成分布式潮流计算,保证各个子网络潮流计算模型的独立性。对IEEE标准系统进行潮流计算的结果表明该法具有较高的收敛速度和计算精度,适合网络计算环境。     

新型电力系统下多分布式电源接入配电网承载力评估方法研究

随着光伏和风电等多种分布式电源的接入,使得传统配电网的结构及其运行状态发生了较大改变。因此,通过建立直观的分布式电源接入评价体系,对新型电力系统背景下的配电网接入分布式电源的承载力进行合理评估成为重要的研究内容。以可再生能源及无功补偿装置接入的新型配电网中风电和光伏发电的最大容量为目标函数,建立分布式电源接入配电网的承载能力模型,通过二阶锥松弛将该模型转化为二阶锥规划模型进行求解。然后考虑到配电网运行的优质性、经济性以及灵活性,建立多层次承载能力评估体系,根据模型求解结果计算承载能力评价指标,再通过组合赋权法将评价指标计算结果转化为综合评分。最后通过对IEEE33节点系统配电网模型进行算例分析,结果表明所提评估方法更为全面、有效。     

Selection of TCSC location for secured optimal power flow under normal and network contingencies

This paper focuses on the optimal power flow solution and enhancement of system performance without sacrificing the security of the system via optimal location and optimal sizing of Thyristor Controlled Series Compensator (TCSC) when the system is operating under normal and network contingency conditions. The paper presents a secured optimal power flow solution by integrating TCSC with the optimization model developed under normal and contingency cases. The optimization model developed in this paper is solved by using linear programming method. New indices called Thermal Capacity Index (TCI) and Contingency Capacity Index (CCI) are proposed for placing the TCSC at appropriate location under normal and network contingency conditions respectively. Once the location to install TCSC is identified, the optimal setting of TCSC is determined through the software code written in MATLAB. The proposed approach is carried out on 6-bus, IEEE 14-bus and IEEE 118-bus test systems and the simulation results are presented to validate the proposed method.     

Faster local power flow solutions: the zero mismatch approach

It is shown that faster and highly localized power flow solutions can be obtained by exploring the difference in convergence rate of individual nodes. Nodes whose mismatches are smaller than a certain tolerance are processed as if their mismatches were actually zero. Computational effort is saved by skipping small mismatch computations and using sparse vector techniques for the nonzero mismatches. Since the proposed approach does not rely on network reduction or equivalencing, the accuracy of the solution remains high in all cases. The ZM (zero mismatch) approach can improve the speed of any Newton-like power flow algorithm without degrading solution accuracy. The relative advantage of ZM for contingency cases increases directly with network size. Its main advantage over other localization methods is that it uses the unmodified global factors of the FDPF (fast decoupled power flow) algorithm and requires no equivalents. ZM exploits the physical characteristics of power flows, the numerical characteristics of iterative solutions, and the sparsity of the matrix factors     

A method for parametrized contingency‐constrained optimal power flow (PCCOPF)

This paper presents a method for Parametrized Contingency Constrained Optimal Power Flow (PCCOPF) whose formulation can discriminate unpreventable contingencies, determine the existence of feasible solutions for postcontingencies, and analyze the feasible solution for the contingencies in terms of static sense. The proposed formulation is based on parametrized contingency constraints in which each contingency parameter represents the achievement ratio of each selected contingency. In the formulation, not only parametrized contingency constraints are given by a set of equality constraints which is modified power flow equations, but also the objective is maximization of the sum of the achievement ratios of selected contingencies. Since contingency parameters are treated as decision variables in the proposed method, the information on unsolvability with respect to each contingency can be efficiently obtained. The feasibility and effectiveness of the proposed method are demonstrated on test problems with 4‐bus and 71‐bus systems. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(1): 21–31, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10182