Stability Study of Low Voltage Electrical Distribution Network: Audit and Improvement of DJEGBE Mini Solar Photovoltaic Power Plant in the Commune of OUESSE (Benin)

The supply of quality energy is a major concern for distribution network managers. This is the case for the company ASEMI, whose subscribers on the DJEGBE mini-power station network are faced with problems of current instability, voltage drops, and repetitive outages. This work is part of the search for the stability of the electrical distribution network by focusing on the audit of the DJEGBE mini photovoltaic solar power plant electrical network in the commune of OUESSE (Benin). This aims to highlight malfunctions on the low-voltage network to propose solutions for improving current stability among subscribers. Irregularities were noted, notably the overloading of certain lines of the PV network, implying poor distribution of loads by phase, which is the main cause of voltage drops;repetitive outages linked to overvoltage caused by lightning and overcurrent due to overload;faulty meters, absence of earth connection at subscribers. Peaks in consumption were obtained at night, which shows that consumption is greater in the evening. We examined the existing situation and processed the data collected, then simulated the energy consumption profiles with the network analyzer “LANGLOIS 6830” and “Excel”. The power factor value recorded is an average of 1, and the minimum value is 0.85. The daily output is 131.08 kWh, for a daily demand of 120 kWh and the average daily consumption is 109.92 kWh, or 83.86% of the energy produced per day. These results showed that the dysfunctions are linked to the distribution and the use of produced energy. Finally, we proposed possible solutions for improving the electrical distribution network. Thus, measures without investment and those requiring investment have been proposed.

Reliability Indices Evaluation of LV Distribution System and Inclusion of Protective Devices for Reliability Improvement

This paper analyzes the reliability of low voltage(LV)distribution system of the Sri Lankan power system.Performance of LV distribution systems where mainly domestic consumers depend on the individual components of the system.Failure rates of elements of the system are calculated based on the historical data of the LV distribution system in a semi-urban area.Load point reliability indices are calculated using the analytical method.Consumer-oriented reliability parameters and energy not served,and its cost are determined.As a method of improvement of reliability,inclusion of fuses to the lateral feeders of the main feeder is proposed.Load point reliability indices,consumer-oriented reliability indices,and energy not served are calculated for the distribution system with fuses in lateral feeders.The results are compared with the reliability indices of the present system and analyzed.

Transient Processes in LV Distribution Systems of Nuclear and Conventional Power Plants

The paper shows several typical arrangements and functions of LV distribution in various power plants and analyses of electromechanical dynamic behavior with NEPLAN simulator. The paper was created on the basis of research project Permanent Prosperity （2A-1TP1/139）-Safety aspects of advanced nuclear reactors in support of Ministry of Industry and Trade of the Czech Republic.

基于ACCF-LVD-KT的距离扩展目标运动参数估计与HRRP重构方法

越来越多的空天威胁目标兼具低可观测性和高机动性,因此从低信噪比的距离扩展目标回波中重构高分辨距离像(HRRP)面临很高的技术挑战。文中提出了一种基于相邻互相关-吕分布-Keystone变换的长时间相参积累方法,能够实现变加速运动距离扩展目标的运动参数估计和HRRP重构。首先,利用相邻互相关函数与吕分布实现机动参数估计;然后,根据机动参数估计值进行相位补偿,并联合Keystone变换校正距离徙动;最后,进行相参积累并实现HRRP重构。仿真实验和实测数据处理结果表明:该方法能够实现运动参数估计与HRRP稳健重构。此外,该方法避免了高维参数搜索,计算效率高,具有良好的工程应用前景。

复杂噪声环境下基于LVD的LFM信号参数估计

针对传统的线性调频(LFM)信号参数估计方法平滑交叉项时,会出现参数估计精度降低和计算复杂度增加等问题,该文引入LVD(LV’s Distribution)方法,该方法可以在参数空间直接显示中心频率和调频斜率(CFCR)。LVD首先对对称参数瞬时自相关函数(PSIAF)进行尺度变换,消除信号在时间轴上的线性频率偏移,然后对尺度变换后的时间变量作2维傅里叶变换,将1维LFM信号转化为2维单频信号。信号各分量在LVD平面表现为多个独立尖峰,使交叉项的能量聚集影响可忽略不计,且信号各峰值所在位置对应于各信号分量的中心频率和调频斜率。LVD可有效抑制高斯噪声,但在脉冲性较强的a稳定分布噪声中,该方法在CFCR域的性能退化甚至失效。对此,该文结合分数低阶统计量理论,提出一种a稳定分布噪声环境下的分数低阶LVD新方法。仿真实验表明该方法在高斯噪声和脉冲噪声环境下均可稳定工作,具有较好的鲁棒性。

利用HAF-LVD特性的复杂运动目标ISAR成像算法

在复杂运动目标的逆合成孔径雷达成像中,由于转动矢量的时变会产生方位向的高阶相位项,导致方位成像的严重散焦,传统的距离-多普勒算法和线性调频模型已不再适用.因此,在建立逆合成孔径雷达成像回波信号为立方相位信号形式的基础上,提出了利用高阶模糊函数-吕氏分布特性的逆合成孔径雷达成像算法.首先,根据高阶模糊函数和吕氏分布思想定义了双延时参数化瞬时自相关函数,并利用变尺度操作去除耦合及快速傅里叶变换实现信号能量积累.然后,利用得到的高阶模糊函数-吕氏分布完成运动参数的非搜索估计和目标逆合成孔径雷达成像.由于引入可调整的缩放因子,该算法能够在保证成像质量和运算效率的基础上,有效避免谱模糊,灵活应对更加多变和恶劣的成像环境.仿真结果验证了该算法的有效性.

国际会议中心供配电系统设计探讨

以广州白云国际会议中心国际会堂为例,介绍这类对供电可靠性要求很高的会议中心供配电系统的情况和特点。通过案例分析和比较,探讨供配电系统中10kV中低压系统接线方案、移动发电机、UPS等关键电气设备的设置原则和注意事项。

基于FRT-MLVD的无源雷达机动目标徙动补偿算法

无源雷达机动目标长时间相参积累过程中,目标的运动参数会引起距离徙动和多普勒徙动,导致回波信号能量分散和检测性能恶化。为实现含有第二加速度的变加速运动目标相参积累,提出了一种基于频域序列反转变换(FRT)和改进吕分布(MLVD)的相参积累算法。首先,利用 FRT 去除信号的距离徙动,将回波能量积累至同一距离单元;然后,利用 MLVD 对该距离单元内的回波进行处理,估计出目标加速度和第二加速度;在补偿目标的加速度和第二加速度引起的多普勒徙动后,利用 Keystone 变换(KT)校正目标速度引起的线性徙动,实现距离和速度的估计。仿真结果表明,所提算法可有效补偿无源雷达中机动目标的距离徙动和多普勒徙动,对变加速目标的积累效果和检测概率显著优于现有算法。

Short-time Lv transform and its application for non-linear FM signal detection

A new time-frequency transform, known as short-time Lv transform （STLVT）, is proposed by applying the inverse Lv distribution to process consecutive segments of long data sequence. Compared with other time-frequency representations, the STLVT is able to achieve better energy concentration in the time-frequency domain for signals containing multiple linear and/or non-linear frequency modulated components. The merits of the STLVT are demonstrated in terms of the effects of window length and overlap length between adjacent segments on signal energy concentration in the time-frequency domain, and the required computational complexity. An application on the spectrum sensing for cognitive ratio （CR） by using a joint use of the STLVT and Hough transform （HT） is proposed and simulated.

基于LVD与Zoom-FRFT的多分量LFM信号参数估计

针对基于分数阶傅里叶变换(FRFT)的多分量线性调频信号(MLFM)参数估计方法中计算量大、估算精度低等问题,本文提出了一种基于吕分布(LVD)与高分辨分数阶傅里叶变换(Zoom-FRFT)的参数估计方法。首先,对MLFM信号进行LVD,检测存在的分量个数,对各分量参数粗略估计,利用粗略调频斜率代入FRFT的参数估计公式,反向计算出FRFT的粗略变换阶次。然后,以粗略变换阶次为中心限定范围,设置精度,连续进行FRFT,从而提取峰值的坐标即精确变换阶次与粗略FRFT域坐标。最后,在精确变换阶次下,以粗略FRFT域坐标为中心限定区间,进行Zoom-FRFT,从而提取精确FRFT域坐标,对分量的参数进行精估计。仿真结果表明,该方法可以有效地对MLFM信号进行参数估计,并可以根据实际需要选择变换阶次的搜索范围与精度、FRFT域的细化倍数;与传统方法相比,本方法同时提高了参数估计精度与计算效率。

含ISOP-DAB变换器的中低压直流配电系统阻抗建模及稳定性分析

“双碳”目标下,高比例可再生能源和高比例电力电子设备成为中低压直流配电系统的主要特征,使得系统因其低惯量、弱阻尼的特性所引起的稳定性问题尤为突出。为此,针对含输入串联输出并联型双有源桥(ISOP-DAB)变换器的中低压直流配电系统进行阻抗建模并提出一种适用于中低压直流配电系统的稳定性分析方法。首先,建立了ISOP-DAB变换器的二端口阻抗模型以及其他单元的阻抗模型。在此基础上根据系统内各单元的端口特性将中低压直流配电系统等效为2个单母线直流子系统,并得到整个系统在中、低压侧的等效阻抗比,当且仅当该等效阻抗比满足奈奎斯特判据时,系统可稳定运行。最后,基于PSCAD/EMTDC平台搭建了含ISOP-DAB变换器的中低压直流配电系统的时域仿真模型,通过仿真实验以及理论计算对比分析了恒功率负载及线路参数对系统稳定性的影响。仿真结果验证了ISOP-DAB变换器的小信号模型以及所提稳定性分析方法的准确性和有效性。

A Real-Time Power Controller for Grid-Connected Inverters in LV Smart Microgrids

This paper presents a real-time power flow controller for VSIs （voltage source inverters） interfaced to low voltage microgrids. The proposed controller is modular, flexible, intelligent, inexpensive, portable, adaptive and designed to positively contribute in low voltage microgrids in which the lines R/X ratio is greater than the transmission lines. Therefore, the proposed control strategy is developed for operation in distribution lines. The controller strategy is different from the conventional grid-connected inverters which are designed based on transmission line characteristics. This controller, using a Texas Instrument general purpose DSP （digital signal processor）, is programmed and tuned using MATLAB/SIMULINK in order to enhance self-healing, reliability and stability of the grid. This general purpose controller makes proper decisions using its local measurements as the primary source of data. The controller has the capability of communicating with the adjacent controllers and sharing the information if/when needed. The power flow output of the inverter is tested for both islanded and grid-connected modes of operation. The inverter positively contributes to active and reactive power supply while operating in grid-connected mode. The proposed control method has been implemented on a Texas Instrument DSC （digital signal controller） chip and tested on a hardware test bench at the Alternative Energy Laboratory at WVU1T （West Virginia University Institute of Technology）. The system＇s experimental results veri~ the validity and efficiency of the proposed controller.

基于线性规划的中低压不平衡配电网电压无功实时优化

高间歇性、高波动性分布式电源(distributed generation,DG)的持续大量接入给配电网的无功电压管理带来严峻挑战,对无功优化的时效性提出了更高要求。现有电压无功控制研究普遍基于单一电压等级和三相平衡网络模型假设,但实际中低压配网两侧的DG、负荷通过配电变压器的耦合互动不断加剧。同时,由于换相缺失、线路不对称布置、负荷及DG不均匀接入等因素,配电网不平衡特性日益加剧,沿用单一电压等级和三相平衡网络可致电压无功控制决策结果不合理甚至不可行。为此,提出一种基于线性规划的中低压不平衡配电网电压无功实时优化方法。具体通过中压配网静止无功发生器(static var generator,SVG)和低压配网分布式光伏逆变器的协调控制,在满足电网运行约束和控制设备能力约束的情况下,实现中低压不平衡配电网节点电压偏差的最小化。同时,为满足高间歇性DG接入对电压无功控制实时性的要求,对上述非线性电压无功优化问题进行线性化逼近,并采用CPLEX求解器对相应线性规划问题进行有效求解。最后,基于某澳大利亚真实配网开展24h仿真,验证了所提基于线性规划的中低压不平衡配电网电压无功实时优化的有效性和优越性。

基于时频分析的雷达非匀速运动目标参数估计

针对合成孔径雷达(SAR,synthetic aperture radar)地面非匀速运动目标参数估计问题,提出了基于吕分布(LVD,Lv′s distribution)的自适应陷波器(ANF,adaptive notch filter)方法。首先,根据地面非匀速车辆目标运动情况建立雷达回波数学模型,并分析推导了回波信号多普勒参数和运动参数的理论公式;其次,利用伪魏格纳分布(PWVD,pseudo Wigner-Ville distribution)算法提取回波信号中由高阶运动引起的高阶相位,通过多项式拟合方法进行补偿,并对运动补偿后的动目标信号沿方位向进行孔径分割,对各个子孔径数据块分别进行基于吕分布算法时频表示,估计得到多普勒调频率值的变化曲线;再利用自适应陷波滤波器对调频率信号中由运动目标的径向加速度引起的高频分量和由航向速度引起的低频分量进行精确分离;最后,对提取的调频率高低频分量进行反演计算,得到非匀速运动目标的径向加速度和航向速度估计值。将本文所提方法与基于吕分布低通滤波器方法进行对比实验,验证本文所提方法在运动参数估计方面取得了更高精度。

可通信式智能选择性漏电保护系统的研究

分析了目前矿井低压电网漏电保护系统存在的不足 ,提出了基于附加直流电源检测和零序功率方向的漏电保护新判据 ,介绍了基于这些新判据的智能漏电保护装置 ,该装置构成的可通信式漏电保护系统可以实现无级差的选择性漏电保护 。

基于大数据的低压配电网无功运行评价体系

我国低压配电网无功运行补偿方式多样,且补偿设备相对分散,无功运行的管理工作存在一定难度,低压配电网的无功运行缺乏有针对性的评价体系,亟需完整科学的方法进行指导。针对上述问题和需求,文章提出了基于电力大数据的包含数据层、指标层和应用层的完整的低压配电网无功运行评价体系。该体系充分发掘了大数据技术在无功运行评价的应用价值,并通过对评价对象的网格划分和评价指标的完整构建,最终实现了对低压配电网格单元的横向比较,将低压配电网的无功运行管理工作推向科学化与精细化。将该评价体系应用于某区域低压配电网算例,验证了其合理性,并可以结合电力大数据的优势,为低压配电网的无功运行管理提供更加有针对性的评价和科学有效的指导。

中压配电变压器优化规划

建立了城市电网中压百己电变压器位置、容量和供电范围优化规划的模型，然后在此基础上给出了求解这一大规模、非线性混合整数规划问题的实用的、大范围自动寻优的三角连续分割算法。实际算例表明，该模型和算法能更好地满足规划的要求。

基于零序电流方向的选择性漏电保护系统的研究

在分析国内外漏电保护装置现存问题的基础上，文章提出了一种基于零序电流方向的矿井低压电网选择性漏电保护系统，重点讨论该系统的工作原理、硬件结构、软件设计及抗干扰技术。最后介绍试验结果和应用情况。

山区配电变压器防雷措施探讨

分析了山区配电变压器易遭雷害的主要原因,提出了山区配电变压器加强防雷保护的措施。

矿井电网过电流特征分析及其保护系统的研究

分析了电网中过电流的故障特征 ,描述了过电流保护系统的工作原理 .重点介绍了对称短路相敏保护特性曲线的确定方法 ,设计了负序电流滤波器 ,建立了过负荷保护的数学模型 .给出了以单片机为中央控制单元所构成过电流保护系统的硬件结构和软件框图 ,下井前对保护系统进行了试验 ,动作指标符合设计要求 ,提高了保护灵敏度 ,增加了保护范围 .现场运行表明 ,该保护系统性能稳定 ,动作可靠 。