基于改进LHS的半不变量法概率潮流计算

为提高概率潮流算法的精度和效率,提出一种将半不变量法和改进的拉丁超立方采样技术相结合的方法.首先,提出改进的非参数核密度估计算法,并用其建立光伏输出功率概率模型.其次,为改善各阶半不变量的计算精度和效率,根据输入随机变量的分布情况的不同,分别采用不同方法计算随机变量的各阶半不变量,并结合Gram-Charlier级数展...     

Probabilistic power system production cost and reliabilitycalculation by the Z-transform method

The authors describe a novel method of probabilistic power system production cost and reliability calculation using the Z transform. In the proposed method, the generating unit available capacity probability density functions (PDFs) are represented by probability impulses. These PDFs are convolved using the Z transform to produce equivalent capacity PDFs. By operating the equivalent capacity PDFs on the system demand, the unit energies, loss of load probability (LOLP), and expected unserved energy (EUE) can be calculated for each load level and the total demand. The method is compared with the cumulant method and Calebrese's traditional direct convolution procedure in terms of accuracy and computing time using the IEEE Reliability Test System. The main advantage of the new method is that actual load and generator availability data can be used directly, rather than via a mathematical representation such as cumulants. An efficient recursive algorithm using the Z transform procedure has been formulated to allow fast evaluations of convolution and deconvolution of PDFs. In terms of computing time, the new method is not much slower than the cumulant method. LOLP and EUE are also calculated more accurately     

A recursive approach to calculating derivatives of production costand reliability of generation system

A recursive computational procedure derived from the cumulant method for efficiently calculating production cost and reliability derivatives is proposed. The procedure is applicable to the derivatives with respect to load, unit capacity, or forced outage rate. Moreover, the procedure can handle any number of cumulants without additional theoretical development or software implementation effort. The general accuracy of cumulant method extended for calculating derivatives is evaluated. In addition to the proposed computational procedure, three extended applications of production simulation derivatives are presented     

考虑负荷概率分布的中压配电网安全合环决策方法

针对配电网合环过程中产生的合环电流可能影响电网安全稳定运行的问题,先通过对合环稳态电流与暂态电流的分析推导出安全合环的简化判据,在此基础上提出一种考虑负荷概率分布的中压配电网安全合环决策方法。其中,采用半不变量法计算合环稳态电流的概率分布特性,并在综合考虑安全性与时效性的基础上进行合环决策;对于输入变量的半不变量难以通过传统数值方法求取的问题,提出一种基于历史负荷数据求取其半不变量的方法。最后通过对上海市浦东新区局部配电网的仿真计算,验证了所提方法的有效性和实用性。     

计及可控串联补偿器的系统电压失稳概率研究

可控串联补偿器(TCSC)可以灵活地调节线路潮流,提高系统运行的稳定性,传统分析方法在评估TCSC提高系统静态电压稳定性作用时存在缺陷,无法考虑不确定性因素的影响。因此,建立计及TCSC接入的系统负荷裕度概率模型,考虑运行参数的随机波动,通过半不变量法和Gram-Charlier级数计算负荷裕度概率特征,进而得到电压失稳概率值。分别在常态与故障下对比TCSC安装前后的IEEE39节点系统失稳概率,结果表明,TCSC能有效地提高系统的静态电压稳定性,验证了本文方法的可行性与准确性。     

Modelling solar half-hour data using fourth order cumulants

In this investigation we have two objectives. In the first one, we have developed a new simple and efficient technique to identify the parameters of the moving average (MA) process using the technique of higher order cumulants. The simulation for different orders of MA in the presence of Gaussian noise, for SNR lower than 20 v dB, gives satisfactory results. In the second objective, the proposed method was adopted for modelling half-hour solar radiation recorded in Marrakesh. Accurate design and optimisation of short response time solar energy systems with storage are sensitive to the stationary and sequential characteristics of half-hourly solar radiation. So, in order to benefit from some characteristics of stationary processes, a preliminary transformation was performed on the original data. The proposed method was used to look for a simple and efficient model to represent solar half-hourly radiation sequences needed for many applications in the solar energy field. The Giannakis technique based on cumulant diagonal slices and the partial autocorrelation function of Box & Jenkins and Brockwell & Davis are used for selection of the model order.     

基于线性化前推回代方程的不平衡配电网概率潮流计算

传统半不变量法采用雅可比矩阵表达输入输出变量间的线性关系且假设网络三相平衡。而实际配电网线路的R/X较高,雅可比矩阵极易呈现病态,且单相光伏的高渗透及负荷不均匀分布造成配电网严重不平衡。为此,提出一种基于线性化前推回代方程的不平衡主动配电网概率潮流算法。该算法将三相前推回代潮流方程进行高精度线性化,综合运用半不变量法和Gram-Charlier级数进行配电网概率潮流计算。所提算法基于真实澳大利亚低压不平衡配电网进行24 h Matlab仿真,验证其可行性、高效性及鲁棒性,并抽取2个典型时刻对比分析验证光伏接入对配电网潮流的概率性和配电网运行性能的影响。     

A fast stochastic solution method for the Blade Element Momentum equations for long‐term load assessment

Unsteady power output and long‐term loads (extreme and fatigue) drive wind turbine design. However, these loads are difficult to include in optimization loops and are typically only assessed in a post‐optimization load analysis or via reduced‐order methods. Both alternatives yield suboptimal results. The reason for this difficulty lays in the deterministic approaches to long‐term loads assessment. To model the statistics of lifetime loads they require the analysis of many unsteady load cases, generated from many different random seeds—a computationally expensive procedure. In this paper, we present an alternative: a stochastic solution for the unsteady aerodynamic loads based on a projection of the unsteady Blade Element Momentum (BEM) equations onto a stochastic space spanned by chaos exponentials. This approach is similar to the increasingly popular polynomial chaos expansion, but with 2 major differences. First, the BEM equations constitute a random process, varying in time, while previous polynomial chaos expansion methods were concerned with random parameters (ie, random but constant in time or initial values). Second, a new, more efficient basis (the exponential chaos) is used. This new stochastic method enables us to obtain unsteady long‐term loads much faster, enabling unsteady loads to become accessible inside wind turbine optimization loops. In this paper we derive the stochastic BEM solution and present the most relevant results showing the accuracy of the new method.     

Coordinated generation and transmission expansion planning in deregulated electricity market considering wind farms

This paper deals with a coordinated generation expansion planning (GEP)–transmission expansion planning (TEP) in competitive electricity market. In the proposed method, GEP and TEP are performed at the same time, with consideration of wind farm uncertainty. The uncertainty is modeled by normal probability distribution function (PDF) and Monte-Carlo simulation (MCS) is used to include the uncertainty into the problem. The planning is managed for two master and slave levels. At slave level, all generation company (GENCO) and transmission company (TRANSCO) maximize their profit and then at master level, the system constraints are checked by independent system operator (ISO). In other words, the proposed planning aims at maximizing the expected profit of all GENCOs and TRANSCOs, while considering security and reliability constraints such as reserve margin and loss of load expectation (LOLE). The proposed problem is a constrained, nonlinear, mixed-integer optimization programming and solved by using particle swarm optimization (PSO) method. Simulation results verify the effectiveness and validity of the proposed planning for maximizing GENCOs and TRANSCOs profit in the presence of wind farm uncertainty under electricity market.     

基于增强形态滤波与三阶累积量对角切片谱的风力发电机滚动轴承故障诊断方法

针对大型风力发电机滚动轴承的故障信号受到强背景噪声干扰不易识别的问题,提出一种基于增强形态滤波与三阶累积量对角切片谱相结合的故障诊断检测方法。该方法首先在研究基本形态学算子的基础上,构建一种新的增强型形态学算子（EMDO）;随后利用特征能量因子（FEF）选择出EMDO算子的最优结构元素尺度;最后利用三阶累积量对角切片谱的消噪性能来进一步增强EMDO算子对风力发电机轴承故障信息的特征提取能力。仿真和对比实验结果表明,所提方法能有效消除高斯白噪生的干扰,对提取风力发电机轴承的故障特征信息起到增强的效果。     

A novel and simple building load calculation model for building and system dynamic simulation

Based on polynomial s-transfer functions of transient heat conduction through a building construction, a novel and simple model is developed for building thermal load calculation. The polynomial s-transfer functions are estimated from the theoretical frequency responses of the building construction by frequency-domain regression method. The simple polynomial s-transfer functions are completely equivalent to the hyperbolic s-transfer functions in terms of frequency characteristics. First, the frequency responses of the total transmission matrix are calculated within the frequency range concerned. Then, a set of linear equations is solved yielding a simple polynomial s-transfer function for cross and internal heat conduction. Finally, simple recursive formulae are obtained by inverse Laplace transforms and discretization of the convolution integrals. The coefficients of the model are independent from time step and the time step can be varied according to the requirement during simulation. Validations and comparisons show that this model has fast computation speed and no numerical unstability, and provides high accuracy and good flexibility to the requirement of variable time step.     

基于多项式混沌展开的水文模型参数敏感性分析

针对水文模型参数不确定问题,选取干旱半干旱地区开都河流域为研究对象,提出了基于多项式混沌展开的水文模型参数敏感性分析方法。首先在开都河流域多年气象、水文观测数据的基础上建立SLURP水文模型;然后利用稀疏网格配置法获得配置点对模拟径流量进行多项式混沌展开;最后根据混沌系数计算Sobol指标评估模型参数及其交互效应对径流的影响。结果表明,在参数主效应中选取的参数中Sobol敏感度指标最大的是降雨系数,最小的是深层地下水截留常数;在交互效应中,浅层土壤蓄水容量和降雨系数之间交互效应最强,Sobol敏感度指标最大,浅层土壤截留常数与深层地下水截留常数之间交互效应最弱,敏感度指标最小。     

可压缩流体网络技术在电站仿真系统中的应用

针对火电站实际系统部分流体在流动过程中密度变化大的特点，从基本物理定律出发，介绍了可压缩流体网络的建模方法。考虑了蒸汽、空气、烟气等流体的不同物性、蒸汽在膨胀中湿度变化、散热、摩阻的影响、风机低流量的稳定性和引风系统中煤粉浓度、烟气温度对导纳的影响。该模型已用于大型火电机组的风烟系统和主蒸汽系统的实时仿真。仿真结果表明：模型准确有效地仿真风烟系统和主蒸汽系统的动静态特性，与现场的试验纪录保持一致。该模型适用于电站风烟系统、主蒸汽系统等可压缩流体的全工况实时仿真。     

Optimum photovoltaic array size for a hybrid wind/PV system

A methodology for calculation of the optimum size of a PV array for a stand-alone hybrid wind/PV power system is developed. Long term data of wind speed and irradiance recorded for every hour of the day for 30 years were used. These data were used to calculate the probability density functions of the wind speed and the irradiance for each hour of a typical day in a month. The wind speed and irradiance probability density functions and manufacturer's specification on a wind turbine and a PV module were used to calculate the average power generated by the wind turbine and the PV module for each hour of a typical day in a month. The least square method is used to determine the best fit of the PV array and wind turbine to a given load. On the basis of the energy concept an algorithm was developed to find the optimum size of the PV array in the system     

Probability distribution of wind power volatility based on the moving average method and improved nonparametric kernel density estimation

In the process of large-scale, grid-connected wind power operations, it is important to establish an accurate probability distribution model for wind farm fluctuations. In this study, a wind power fluctuation modeling method is proposed based on the method of moving average and adaptive nonparametric kernel density estimation (NPKDE) method. Firstly, the method of moving average is used to reduce the fluctuation of the sampling wind power component, and the probability characteristics of the modeling are then determined based on the NPKDE. Secondly, the model is improved adaptively, and is then solved by using constraint-order optimization. The simulation results show that this method has a better accuracy and applicability compared with the modeling method based on traditional parameter estimation, and solves the local adaptation problem of traditional NPKDE.     

The simulation error caused by input loading variability in offshore wind turbine structural analysis

Stochastic representations of turbulent wind and irregular waves are used in time domain simulations of offshore wind turbines. The variability due to finite sampling of this input loading is an important source of simulation error. For the OC4 reference jacket structure with a 5 MW wind turbine, an error of 12–34% for ultimate loads and 6–12% for fatigue loads can occur with a probability of 1%, for simulations with a total simulation length of 60 min and various load cases. In terms of fatigue life, in the worst case, the lifetime of a joint was thereby overestimated by 29%. The size of this error can be critical, i.e., ultimate or fatigue limits can be exceeded, with probability depending on the choice of number of random seeds and simulation length. The analysis is based on a large simulation study with about 30,000 time domain simulations. Probability density functions of response variables are estimated and analyzed in terms of confidence intervals; i.e., how probable it is to obtain results significantly different from the expected value when using a finite number of simulations. This simulation error can be reduced to the same extent, either using several short simulations with different stochastic representations of the wind field or one long simulation with corresponding total length of the wind field. When using several short‐term simulations, it is important that ultimate and fatigue loads are calculated based on the complete, properly combined set of results, in order to prevent a systematic bias in the estimated loads. Copyright © 2014 John Wiley & Sons, Ltd.     

A multi-stage stochastic transmission expansion planning method

This paper presents a multi-stage stochastic model for short-term transmission expansion planning considering the available transfer capability (ATC). The ATC can have a huge impact on the power market outcomes and the power system reliability. The transmission expansion planning (TEP) studies deal with many uncertainties, such as system load uncertainties that are considered in this paper. The Monte Carlo simulation method has been applied for generating different scenarios. A scenario reduction technique is used for reducing the number of scenarios. The objective is to minimize the sum of investment costs (IC) and the expected operation costs (OC). The solution technique is based on the benders decomposition algorithm. The N-1 contingency analysis is also done for the TEP problem.The proposed model is applied to the IEEE 24 bus reliability test system and the results are efficient and promising.     

An assessment of failure probability in elastic-plastic conditions where stable tearing has occurred

An analysis is presented for calculating the failure probability of a structure subject to general elastic-plastic loading and where the fracture mode is ductile. The main statistical variables considered are fracture toughness, flow stress and defect size.The analysis is based on a development of the R6 methodology of defect assessment. The concept of a maximum load locus is developed from the failure assessment line. The maximum load locus is used to predict those combinations of materials properties and defect size that might combine to predict structural failure after some stable crack growth. The method of determining the maximum load locus is described and some examples presented.The maximum load locus is used to estimate the failure probability on the first loading of a structure. It is also shown that the maximum load locus can be used to estimate the failure probability of a proof loaded structure where, in general, there may be a change in the dominant failure mode between proof and fault loadings. Detailed examples are presented to illustrate the analysis.     

考虑源荷不确定性的电热系统联合调度

针对风电和电热负荷不确定的问题,提出计及源荷不确定性的旋转备用容量的优化方法,建立考虑电热备用耦合影响的调度模型.在日前阶段,以能源与负荷的预测量制定机组的出力方案,风电由于其预测精度较低,利用Beta概率密度函数来拟合风电出力,从而确定风电的不确定性带来的旋转备用容量,利用机会约束规划来处理不确定问题;负荷有较高的预...     

基于TRNSYS仿真数据的平板型太阳能集热器净得热非参数核密度估计概率模型

平板型太阳能集热器净得热量受天气等外部因素影响而表现出一段时间内的间歇性、随机性和周期性,采用概率建模方法能更准确地反映上述变化特点。目前概率建模中常用的参数分析法需假设先验概率分布,不具有普适性,为此提出一种采用非参数核密度估计对平板型太阳能集热器净得热概率建模的方法。通过TRNSYS动态仿真得到天津地区平板型太阳能集热器净得热样本数据,采用黄金分割算法求解非参数核密度估计的最优带宽,并通过拟合优度检验和误差检验,验证了该概率模型的准确性和在不同时间范围下的适应性。