大电网可靠性评估的灵敏度分析新方法

针对大电网灵敏度难以求解的状况,提出了大电网可靠性评估灵敏度分析新方法,通过系统节点可靠性的元件信息以及连通关系,求得灵敏度的相关信息,进而为电力系统规划和运行提供重要的指导意见。通过36节点算例,验证了该方法评估大电网灵敏度的有效性、可行。     

A method for the automatic segmentation of brown adipose tissue

Objective

Brown adipose tissue (BAT) plays a key role for thermogenesis in mammals and infants. Recent confirmation of BAT presence in adult humans has aroused great interest for its potential to initiate weight-loss and normalize metabolic disorders in diabetes and obesity. Reliable detection and differentiation of BAT from the surrounding white adipose tissue (WAT) and muscle is critical for assessment/quantification of BAT volume. This study evaluates magnetic resonance (MR) acquisition for BAT and the efficacy of different automated methods for MR features-based BAT segmentation to identify the best suitable method.

Materials and methods

Multi-point Dixon and multi-echo T₂ spin-echo images were acquired from 12 mice using an Agilent 9.4T scanner. Four segmentation methods: multidimensional thresholding (MTh); region-growing (RG); fuzzy c-means (FCM) and neural-network (NNet) were evaluated for the interscapular region and validated against manually defined BAT, WAT and muscle.

Results

Statistical analysis of BAT segmentation yielded a median Dice-Statistical-Index, and sensitivity of 89. 92 % for NNet, 82. 86 % for FCM, 72. 74 % for RG, and 72. 70 %, for MTh, respectively.

Conclusion

This study demonstrates that NNet improves the specificity to BAT from surrounding tissue based on 3-point Dixon and T₂ MRI. This method facilitates quantification and longitudinal measurement of BAT in preclinical-models and human subjects.

     

一种反应输电线路故障行波的测距方法

分析了故障暂态电流行波的基本理论,提出了一种故障测距原理,以同母线上任一"有限长"非故障线路作为参考线路,通过比较由故障线路暂态电流行波与该参考线路暂态电流行波形成的反向行波浪涌与其对应的正向行波浪涌的极性,识别来自故障方向的行波浪涌,消除了来自参考线路的暂态行波浪涌的影响。通过以本原理构成的故障测距系统进行实际检验,测距精度明显高于目前故障录波器的测距精度。理论分析和实测波形分析均表明该原理是可行的,并可以同时适用于永久性故障和瞬时性故障,而且不受电压过零故障的影响,在标准模式下还不受线路对端母线反射波的影响。     

Finding all solutions of piecewise‐linear resistive circuits using the dual simplex method

An efficient algorithm is proposed for finding all solutions of piecewise‐linear (PWL) resistive circuits using linear programming (LP). This algorithm is based on a simple test (termed the LP test) for non‐existence of a solution to a system of PWL equations in a given region. In the conventional LP test, the system of PWL equations is transformed into an LP problem, to which the simplex method is applied. However, this algorithm requires a very large number of pivotings because the simplex method is applied on many regions. In this paper, we introduce the dual simplex method to the LP test, which makes the average number of pivotings per region much smaller (less than one, for example) and makes the algorithm very efficient. By numerical examples, it is shown that the proposed algorithm could find all solutions of large‐scale problems, including those where the number of variables is 300 and the number of linear regions is 10³⁰⁰, in practical computation time. Copyright © 2002 John Wiley & Sons, Ltd.     

A novel method for locating the source of sustained oscillation in power system using synchrophasors data

Large interconnected power systems are usually subjected to natural oscillation (NO) and forced oscillation (FO). NO occurs due to system transient response and is characterized by several oscillation modes, while FO occurs due to external perturbations driving generation sources. Compared to NO, FO is considered a more severe threat to the safe and reliable operation of power systems. Therefore, it is important to locate the source of FO so corrective actions can be taken to ensure stable power system operation. In this paper, a novel approach based on two-step signal processing is proposed to characterize FO in terms of its frequency components, duration, nature, and the location of the source. Data recorded by the Phasor Measurement Units (PMUs) in a Wide Area Monitoring System (WAMS) is utilized for analysis. As PMU data usually contains white noise and appears as multi-frequency oscillatory signal, the first step is to de-noise the raw PMU data by decomposing it into a series of intrinsic mode functions (IMF) using Improved Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (ICEEMDAN) technique. The most appropriate IMF containing the vital information is selected using the correlation technique. The second step involves various signal processing and statistical analysis tools such as segmented Power Spectrum Density (PSD), excess kurtosis, cross PSD etc. to achieve the desired objectives. The analysis performed on the simulated two-area four-machine system, reduced WECC-179 bus 29 machine system, and the real-time power system PMU data set from ISO New England, demonstrates the accuracy of the proposed method. The proposed approach is independent of complex network topologies and their characteristics, and is also robust against measurement noise usually contained in PMU data.     

基于PCC控制的无功补偿装置的原理与分析计算方案

介绍一种采用PCC控制的新型动态无功补偿装置。电压、电流信号的测量采用可编程放大器,基准电压进行预处理,方便校正;通过求电压、电流信号的相位差值,计算得到功率因数,实现对电网的实时监控;并采用晶闸管控制投切电容器的方式,对电网功率因数进行自动补偿,提高功率因数。结果表明:采用新型动态无功补偿装置,功率因数大于0.95,改善了电能质量、降低了损耗。     

基于PCC控制的无功补偿装置的原理与分析计算方案

介绍一种采用PCC控制的新型动态无功补偿装置.电压、电流信号的测量采用可编程放大器,基准电压进行预处理,方便校正;通过求电压、电流信号的相位差值,计算得到功率因数,实现对电网的实时监控;并采用晶闸管控制投切电容器的方式,对电网功率因数进行自动补偿,提高功率因数.结果表明:采用新型动态无功补偿装置,功率因数大于0.95,改善了电能质量、降低了损耗.     

Real-time measurement of power disturbances: Part 2. Implementation and evaluation of the novel complex filter/recursive algorithm

The novel complex filter/recursive algorithm, which are proposed in part 1 of the two-part series, is an improved signal processing technique that can accurately and continuously measure the instantaneous electrical quantities such as the amplitude, phase angle, frequency and power of the fundamental and harmonic components even during power disturbances. This paper, which is part 2 of the series, focuses on the ways to implement the proposed method for real-time applications. Further, the effectiveness and superiority of the proposed method over the well-known Fourier Algorithm (FA) and the Morlet wavelet-based Continuous Wavelet Transform (CWT) are also ascertained in this paper using both simulated and practical power disturbance waveforms.     

基于波形识别原理的高灵敏度差动保护方法

针对风电场中性点经高阻接地系统汇集线母线单相故障时常规母线差动保护灵敏度不足的问题,提出一种基于波形识别原理的高灵敏度差动保护方法。该方法识别故障波形特征,根据负荷情况实时调整浮动门槛值,同时,根据系统谐波含量实时调整差动比率系数,有效避免因谐波引起的高灵敏度差动保护误动作。RTDS的仿真结果表明,该方法能够保证中性点经高阻接地系统在发生单相故障时,迅速切除故障。该方案的应用,对于保护电气设备、维护风电系统稳定运行具有重要意义。     

AFDX交换机测试系统的原理及方法

AFDX是空客公司根据航空电子发展的需求以以太网为基础,通过在实时性、可靠性等方面进行改进而建立起来的一种高性能航空数据总线,基于该总线的航空电子系统通过AFDX总线交换机可实现终端间的网络化互联。在实际应用中,由于AFDX总线交换机的性能指标直接影响着整个系统的传输性能,因此需要对AFDX总线交换机的性能进行综合测试。为此,本文首先详细的介绍了ARINC664协议对AFDX交换机功能和性能的分解,进而对AFDX交换机的测试需求及测试方法进行了分析,在此基础上,构建了一套AFDX交换机测试系统,并对其软硬件组成及测试方法进行了详细介绍。     

A novel method for predicting the lifetime of MOV

The paper presents a methodology for predicting the lifetime of metal-oxide varistor (MOV) which is widely used as a protective material in high-voltage equipment. The methodology is based on the characteristic time-current curve which is determined by the characteristic currents obtained from multistressed aging experiments. Results show that the proposed method is more effective and reliable than those adopted previously.     

基于波形间断角原理识别变压器励磁涌流的新方法

本文提出了一种利用波形间断角原理和模糊贴近度原理相结合识别励磁涌流的新方法。该方法的基本思路是,对于理想的故障电流,其任意半周期的面积为一个整周期面积的1/2,而励磁涌流波形由于间断角的存在,没有上述特点,基于此再结合模糊贴近度原理实现故障电流和励磁涌流的区分。仿真结果表明,该算法特征明显,易于工程实现,而且鉴别准确。     

一种测量纳米材料高频特性的新方法

本文介绍一种使用同轴线制备简易高频测试平台、运用射频设备测量纳米尺度样品高频性能的方法。使用该方法,窄脉冲射频信号在传输线中的延时测量精度达到10皮秒左右,发现了铜芯同轴传输线与多壁碳管同轴传输线的传输特性的区别。这一方法有可能推广到测试其他小尺度样品高频特性的研究中。     

备用和电能量灵活联合调度及定价新方法

对电力市场条件下目前实时交易的备用需求、调度和定价进行简述。提出考虑发电机组约束的一种用于事故备用的电能量和备用灵活联合调度和定价新方法，此方法的最大优点在于它考虑了发电机的最大和最小发电容量以及与备用直接关联的爬坡率和可调旋转备用需求，比排队法、顺序法更符合实际。数据仿真结果验证了所提方法的有效性。     

直流CT电子测量单元的工作原理及校验方法

±500kV直流输电工程中的直流测量设备是直流控制保护系统的重要组织部分,其计量的准确性,是判别直流系统运行状况,调整直流系统运行参数和运行方式的主要依据;直流CT电子测量单元在技术上采用了先进的电子技术和零磁通原理,主要由高电压绝缘特性的铁芯和线圈组成,是测量直流量的宽频带测量装置;该测量单元的校验主要包括性能和准确度的校验,性能校验是利用数字仪表和示波器对其各具有的功能进行检查,确立其能否满足运行工况及技术指标的要求,准确度的校验是利用标准装置采用直接比较法对其校准绕组进行检测.本文通过对直流CT电子测量单元的原理分析,确定其准确度及技术性能的校验方法,为电网的安全经济运行提供可靠的保证.     

基于双空间的融合特权信息支持向量机模拟电路故障诊断

针对模拟电路故障诊断识别率较低的问题,提出了基于双空间特征提取的融合特权信息支持向量机的模拟电路故障诊断新方法。首先对采集的信号进行主成分分析(principal component analysis,PCA)——特征提取;并用融合特权信息支持向量机LUPI-SVM(SVM of learning using privileged information,LUPI-SVM)分类器和SVM-GA分类器进行预分类;对分类结果不同的样本进行独立成分分析(independent component analysis,ICA)—特征提取,并用LUPI_SVM进行分类识别,Sallen-Key滤波电路故障诊断仿真实验结果表明该方法有效提高了分类的性能,为模拟电路故障诊断提供了新的途径。     

A novel method for SLG fault location in power distribution system using time lag of travelling wave components

This paper presents an approach to single line‐to‐ground fault location in a power distribution system based on the time lag of different modal components . It is a single‐ended method applicable to unsynchronized measurements. The fault location formulation is derived by analyzing the traveling wave propagation characteristic in a distributed parameter model. To tackle the key problem of ground‐mode velocity estimation, an iterative velocity method based on prior knowledge is first proposed. Since the practical measurements are not ideal because of sensor accuracy and nonequivalent transient response, fuzzy neural network is utilized to process traveling wave data acquired at multiple measurements to get an error‐tolerant effect. Furthermore, electromagnetic transient simulations for a 34‐bus test feeder system under various conditions of fault resistances, inception angles, and distributed generator access reveal the robust estimation of fault location. The performance of the proposed method is also validated by simulations with noisy and noise‐free measurements. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A review of heart chamber segmentation for structural and functional analysis using cardiac magnetic resonance imaging

Cardiovascular magnetic resonance (CMR) has become a key imaging modality in clinical cardiology practice due to its unique capabilities for non-invasive imaging of the cardiac chambers and great vessels. A wide range of CMR sequences have been developed to assess various aspects of cardiac structure and function, and significant advances have also been made in terms of imaging quality and acquisition times. A lot of research has been dedicated to the development of global and regional quantitative CMR indices that help the distinction between health and pathology. The goal of this review paper is to discuss the structural and functional CMR indices that have been proposed thus far for clinical assessment of the cardiac chambers. We include indices definitions, the requirements for the calculations, exemplar applications in cardiovascular diseases, and the corresponding normal ranges. Furthermore, we review the most recent state-of-the art techniques for the automatic segmentation of the cardiac boundaries, which are necessary for the calculation of the CMR indices. Finally, we provide a detailed discussion of the existing literature and of the future challenges that need to be addressed to enable a more robust and comprehensive assessment of the cardiac chambers in clinical practice.