A novel approach of reference current generation for power quality improvement in three-phase, three-wire distribution system using DSTATCOM

This paper presents a novel approach based on an improved instantaneous active and reactive current component theory for generating reference currents for distribution static compensator (DSTATCOM). Three-phase reference current waveforms generated by proposed scheme are tracked by the three-phase voltage source converter in a hysteresis band control scheme. The performance of the DSTATCOM using the proposed control strategy has been evaluated under various source and load conditions. The performance of the proposed control strategy has been evaluated in terms of load balancing, reactive power compensation, compensator rating and harmonic mitigation. A three-phase, three-wire distribution system supplying star connected linear as well as non-linear unbalanced load is considered for simulation study. The detailed simulation results using MATLAB/SIMULINK software are presented to support the feasibility of proposed control strategy.     

Selection of minimal tripping times for distance protection using fault trees with time dependencies

Correct coordination between protection relays is an essential requirement to maintain stability and integrity of electrical power systems. Time settings of protection relays have to be adapted to time characteristics of electrical power systems and time settings of other protections. In the paper, fault trees with time dependencies (FTTD) are used for selecting time delay settings of remote back-up distance protections. In FTTD, events and gates are characterized by time parameters, which are derived from time characteristics of protection devices and the inherent delays of protection equipment. Two case studies are presented. First, the coordination of protections for the simple transmission line composed of two identical sections is studied. Next, the transmission line that contains two sections of different lengths and transformer between them is analyzed. In both cases, formulae for time delays of protections are derived. According to calculations executed for the first case, our method gives time delays that often are significantly smaller than values suggested by generally recommended and accepted rules.     

安森美半导体应用于LED区域照明的电源、保护及联网方案

本文介绍了安森美半导体LED区域照明应用中的电流可调节恒流功率因数校正及超高能效大功率等驱动电源方案,LED串保护方案以及联网型LED街灯控制方案。     

保护用电流互感器饱和特性及其误差曲线研究

当电力系统发生故障时,一次电流比正常运行时的电流大几倍甚至几十倍,此时,保护用电流互感器的铁芯发生饱和,引起二次电流的畸变,从而使继电保护及其二次设备误动作。笔者对保护用电流互感器的误差与饱和特性进行了分析,介绍了实际工作中电流互感器误差曲线的绘制以及二次负载的校核方法,并提出了减小电流互感器误差的具体措施。     

一起单相接地引起消弧线圈事故分析

对某变35 kV系统一起消弧线圈单相接地事故作了分析,在此基础上对消弧线圈阻尼电阻的选取提出建议,可供实际应用参考。     

基于灰关联性理论的小电流单相接地故障选线及其仿真

传统的、基于待测的故障特征量的小电流单相接地故障选线方法存在局限性,针对此问题,提出一种基于灰色理论、融合多种判据、有效利用已有的故障特征量的选线方法,以各出线、母线单相接地故障的电流、电压等特征量组成选线系统的典型接地故障样本,通过待测样本与比较样本之间的关联度判断所属状态,然后利用灰关联序来判断故障线路。利用电力系统计算机辅助设计(power system computer aided design,PSCAD)软件与Matlab软件进行仿真实验,实验结果验证了该方法可靠、有效。     

高压直流输电系统中的全桥直流变压器研究

研究了一种高压直流输电系统中的重要组成部分,即直流变压器。全桥直流变压器具有输入输出电压成比例,易于实现软开关等优点。详细分析了全桥直流变压器的工作原理,介绍了电流连续和断续两种工作模态,讨论了全桥直流变压器的输出特性以及漏感的选取,并在此基础上进行了实验验证,分析了影响直流变压器特性的因素。实验结果表明,直流变压器可以实现功率的传输和电压的提升,适用于高压输电系统。     

斜线PWM及其派生电流跟踪方法

对用于电压型脉宽调制（pulsewidthmodulation,PWM）变换器的滞环法进行分析。首先提出抛物线PWM电流跟踪方法,该方法将抛物线状的电流环与纹波电流（误差电流）比较产生开关频率基本恒定的PWM信号,并进而提出开关频率更稳定的改进抛物线法,最后提出斜线法,该方法将纹波电流斜率与斜线状的电流环比较,产生开关频率基本恒定的PWM信号,且能在一个开关周期内使变换器电流精确跟踪电流指令值。以半桥电压型PWM变换器为例,仿真验证了上述方法的有效性。     

基于间接矢量控制的感应电机高速弱磁区电流控制

感应电机弱磁高速运行,由于低磁场、强耦合和大时滞的影响,使得目前的间接矢量控制系统难以实现电流有效控制。针对5～6倍基速及以上速度运行时的电流控制问题,考虑电压、电流、参数变化以及转速等多状态的耦合影响,以基于模糊推理的专家系统,构建电流给定自整定控制器,即使在整定失败的情况下也可以使用一个次优参数替代,克服了一般专家系统存在无法找到满足性能指标参数,导致整定失败的缺点,通过控制器对电流给定进行预处理,保证电流的有效跟随,提高电流控制的稳定性。最后进行仿真和物理实验验证,结果表明本方法具有有效性和实用性。     

基于内模原理的自适应电流检测系统研究

传统自适应电流检测方法因受到低信噪比检测环境引起的交互式误差干扰的严重影响,难以兼顾检测方法的快速性和精确性。本文提出了一种新颖的自适应电流检测方法,引入滑动积分滤波器(SIF)消除谐波电流的干扰,并获取基波有功、无功电流幅值估算误差。基于内模控制原理构成有功、无功电流的自适应检测闭环系统,快速、准确地分离提取畸变负载电流中的目标电流分量。文中对所提出的自适应电流检测方法建立了数学模型,并基于控制理论中的方法对本文电流检测方法的收敛性及其快速性、精确性进行了理论分析,为自适应电流检测方法的性能设计提供了理论指导。最后,通过仿真和实验证明本文所提出理论和方法的正确性与有效性。