An efficient method to compute closest loadability limit in power systems

A closest loadability limit (CLL) is considered as a most reliable index in the assessment and enhancement of voltage stability of a power system. Two kinds of methods, the iterative method and the direct N‐R method, have been proposed so far, but the computation of CLL is known to be troublesome. The former method is quite time‐consuming and its convergence is sometimes distributed due to the existence of multiple local CLLs, while the latter method is hardly useful unless a very accurate initial condition is available. This paper proposes a new method to compute a CLL, consisting of three stages of computations. The first stage is to obtain a rough initial estimate of a CLL, where multiple local CLLs can be approximated by the multiple load flow solutions. The initial estimate is refined by the second stage computation based on a method similar to the conventional iterative method. The third stage is to obtain a direct solution by mean of the N‐R method. The effectiveness of the proposed method is demonstrated using IEEE 14, 30, 57, and 118 bus test systems. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(1): 57–67, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1171     

极限诱导分岔最小负荷裕度计算方法

由于极限诱导分岔点处的潮流雅可比矩阵非奇异,因此电压稳定裕度对参数灵敏度的计算存在困难。对此,采用分岔点处参数灵敏度计算的新方法,只需求解一个左端系数阵为扩展潮流雅可比矩阵的线性方程组,进而提出了包含极限诱导分岔点在内的静态电压稳定最小负荷裕度计算方法。该方法结合负荷增长模式及其波动形式,建立了连续潮流模型和求取最小负荷裕度的优化模型。IEEE 118节点系统的仿真算例验证了所述方法的简单有效性。     

Monte Carlo simulation of electrical corona discharge in air

Electrical discharges play a key role in technologies; there are many industrial applications where the corona discharge is used. Air as insulator is probably the best compromise solution for many applications. All of this reflects on the great importance of the evaluation of the corona performance characteristics. Numerical simulation of the corona discharge helps to better understand the involved phenomena and optimize the corona devices. This paper is aimed at calculating the corona discharge in negative point-plane air gaps. To describe the non-equilibrium behavior of the electronic avalanches and to simulate the development of corona discharge the method of Monte Carlo has been used. This model provides the spatial-temporal local field and particles charged densities variations as well as the ionization front velocity.     

基于蒙特卡罗随机选线最优潮流的电压崩溃临界点算法

提出了基于蒙特卡罗随机选线最优潮流的电压崩溃临界点算法.在最优潮流的基础上,融入蒙特卡罗随机选线以及基于负荷预测的负荷正态分布,以系统能够承受的最大负荷为目标函数,对由负荷的不确定性导致的变量随机性建立起相应的机会约束规划,采用非线性规划方法对目标函数进行优化,直接求得满足某一概率约束下的系统最大负荷.以IEEE3机9...     

Evaluating the integration of wind power into distribution networks by using Monte Carlo simulation

This paper provides a probabilistic method to assess the impact of wind turbines (WTs) integration into distribution networks within a market environment. Combined Monte Carlo simulation (MCS) technique and market-based optimal power flow (OPF) are used to maximize the social welfare by integrating demand side management (DSM) scheme considering different combinations of wind generation and load demand over a year. MCS is used to model the uncertainties related to the stochastic variations of wind power generation and load demand. The market-based OPF is solved by using step-controlled primal dual interior point method considering network constraints. The method is conceived for distribution network operators (DNOs) in order to evaluate the effect of WTs integration into the network. The effectiveness of the proposed method is demonstrated with an 84-bus 11.4 kV radial distribution system.     

A new formulation and solution method for the maximum loading point in electrical power systems

This paper proposes a new efficient formulation and solution method for a maximum loading point or saddle node bifurcation point in electrical power systems. This point, corresponding to a tip of the P(Q)-V curve, is characterized by singularity of the load flow Jacobian. The proposed formulation is of dimension n + 1, instead of 2n + 1 in the standard formulation, for n-dimensional load flow equations. The proposed method uses a 1-dimensional singularity condition, obtained from a reduction of the standard n + 1-dimensional singularity conditions. For this reduction, one of the diagonal elements of the load flow Jacobian is selected. We also propose an index for this selection to make the proposed method reliable. The solution for the proposed formulation can effectively be obtained based on the Newton-Raphson method with sparse matrix techniques. The computational performance of the proposed method is demonstrated on 6, 14, and 118 bus test systems. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 121(1): 17–25, 1997     

基于拟蒙特卡罗和半不变量法的概率潮流计算

为实现含风电出力电网概率潮流计算精度的提高,提出一种结合拟蒙特卡罗和半不变量的方法。建立风电出力模型,采用拟蒙特卡罗模拟法(QMCS)抽取Sobol确定性低偏差点列,结合半不变量法,算出节点状态变量以及各支路潮流的半不变量,引入Gram-Charlier级数,以概率潮流计算为工具,对相关节点电压进行模拟,并与传统蒙特卡罗模拟(MCS)方法和MCS结合半不变量法对比。算例表明,相同抽样次数下QMCS结合半不变量法的计算结果更接近真解,并且计算速度相对更快。     

An improved method to approximate closest saddle node bifurcation based on multiple load flow solutions: A new method of voltage stability monitoring and control

Although a closest bifurcation point (CBP) is known to be a superior security measure against voltage collapse, no fast computation methods exist presently. In such a circumstance, the authors proposed an approximation method for CBP in Ref. 11 where two major problems were left unsolved: (1) the method cannot take into Q limits of generators and (2) it utilizes a low‐voltage power flow solution, which is not easily obtained unless a suitable initial estimate is available. This paper presents a series of techniques to solve these problems. It is shown that the proposed method can provide fairly accurate CBP without suffering any major problems. The total computation time is not more than that of ten power flows even when no information of low‐voltage solution is available in advance. The proposed method will make possible a reliable on‐line monitoring and control of voltage stability. © 2000 Scripta Technica, Electr Eng Jpn, 133(1): 19–30, 2000     

Monte Carlo simulation-based probabilistic assessment of DG penetration in medium voltage distribution networks

With the growing use of renewable energy sources, Distributed Generation (DG) systems are rapidly spreading. Embedding DG to the distribution network may be costly due to the grid reinforcements and control adjustments required in order to maintain the electrical network reliability. Deterministic load flow calculations are usually employed to assess the allowed DG penetration in a distribution network in order to ensure that current or voltage limits are not exceeded. However, these calculations may overlook the risk of limit violations due to uncertainties in the operating conditions of the networks. To overcome this limitation, related to both injection and demand profiles, the present paper addresses the problem of DG penetration with a Monte Carlo technique that accounts for the intrinsic variability of electric power consumption. The power absorbed by each load of a medium voltage network is characterized by a load variation curve; a probabilistic load flow is then used for computing the maximum DG power that can be connected to each bus without determining a violation of electric constraints. A distribution network is studied and a comparison is provided between the results of the deterministic load flow and probabilistic load flow analyses.     

基于蒙特卡罗的电力市场双边交易竞价策略研究

在批发竞争市场环境下,研究双边交易市场中经纪人的交易策略.分析经纪人交易原理、类型、报价规则及社会效益.通过蒙特卡罗方法模拟研究买卖双方的最优报价策略,并用一个算例验证报价策略的有效性.     

含风电场电力系统的Cornish-Fisher级数概率潮流计算

利用基于Cornish-Fisher级数展开的方法研究了含风电场电力系统的概率潮流分布问题.该方法以半不变量为纽带,构建了待求变量和已知变量之间的直接耦合关系;以确定性的潮流计算为出发点,得到了具有较高精度的概率潮流分布结果.仿真计算表明:与基于蒙特卡洛仿真抽样法的概率潮流计算方法相比,在保证计算结果精度的前提下,该方...     

A study on economic load dispatch based on power flow constraint with the N‐1 criterion considering correlation among wind farms

This paper presents a new method of economic load dispatch (ELD) for preventing the overload on transmission lines with the N‐1 criterion in power systems penetrated with a large number of wind farms (WFs) from a stochastic perspective. There is a possibility that uncertain output variations in WFs according to the wind speed change cause overloading of the transmission lines. Furthermore, since the output variations in WFs can be expressed by stochastic models, the occurrence of the overload must be also assessed by stochastic means considering the operation of power systems. With the N‐1 criterion, when the overloading probability is over a predefined acceptable value, the power flow must be resized by changing the load dispatch so that the overloading probability becomes below the predefined acceptable value. Hence, in this paper, we develop a new methodology regarding ELD which can satisfy the N‐1 criterion under the uncertainty of output variations in WFs by Monte Carlo simulation considering correlation among WFs. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A model for numerical evaluation of the global stability region in power systems determined by a nonlinear limit cycle

A power system is a large dynamic system, which includes many nonlinear elements. According to the nonlinear analyses using Hopf bifurcation theory, it can be detected that a limit cycle exists around an operating point, which may affect the global stability of a power system significantly. The authors have presented a numerical method to analyze the nonlinear characteristics in power systems by observing the power swing after some perturbation where the coefficients of nonlinear terms are determined by the least squares method. In this paper the method is modified for the application to a longitudinally interconnected power system including an excitation system, and the influence of the excitation voltage limiter on the nonlinear phenomena of the whole power system can be detected by some numerical analyses. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(3): 17–27, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10193