基于光通量特征参数比对的IEC闪变仪适用性分析方法

传统IEC闪变仪在检测由间谐波引起的闪变的准确性上存在不足。针对IEC闪变仪的适用范围及间谐波引起的闪变算法进行了研究。通过搭建IEC闪变仪检测模型及光通量数学模型,测得调幅波和间谐波下的闪变测量值、光通量波动频率及波动值,对调幅波引起的闪变值和光通量数据进行多变量数据拟合,得到光通量与闪变之间的关系,并将其作为光通量与闪变之间的标准关系式。依据标准关系式探讨了IEC闪变仪在检测间谐波引起的闪变时的适用性,采用基于升-降采样及峰值检测相结合的方法,弥补了IEC闪变仪在检测由间谐波引起的闪变的不足。     

间谐波导致的闪变特征及闪变限制曲线

电力系统中广泛使用的变频装置产生的间谐波导致了不容忽视的电能质量问题--电压闪变。依据白炽灯热平衡方程,对含间谐波电压作用下白炽灯输出光通量的时变波形进行了理论分析。研究表明,高、低频间谐波电压都可能造成白炽灯闪变,且间谐波幅值和频率、与间谐波最靠近的谐波次数及其奇偶性都是影响光通量波动频率和波动深度的因素。基于IEC闪变仪标准和光通量波动特征与电压间谐波分量参数的关系,提出了间谐波的闪变限制曲线。     

基于热平衡方程的改进的白炽灯闪变仪模型

IEC闪变仪作为闪变强度测量的国际标准被广泛接受.但存在对高频间谐波造成的闪变不能测量的缺陷.文章根据IEC闪变仪的工作过程分析了导致这种缺陷的原因,并基于白炽灯的热平衡方程及其热辐射发光特性,建立了能反映间谐波电压影响的白炽灯光通量表达式,进而提出了闪变仪的改进模型.模型的计算机仿真结果与实验结果的比较表明,改进的白炽灯闪变仪模型能有效地克服IEC闪变仪的缺陷.     

On the phase sequence characteristics of interharmonics

Phase sequence is an important attribute of voltages and currents in three phase power systems. This paper investigates the sequence characteristics of interharmonic components. Three common cases involving interharmonics are analyzed. These are variable frequency drives (VFD), motors with fluctuating mechanical loads and general fluctuating impedance loads. The results reveal that interharmonics can have either positive or negative sequence and are rarely zero sequence. Its sequence cannot be determined by examining the interharmonic frequency alone. The general rule is that the sequence of interharmonics is the same as that of the supply system harmonic components being modulated. If the resulting interharmonic frequency produced by the modulation process is negative, the sequence of the interharmonic component will change from positive to negative or vice versa. The findings of this paper will help to improve our understandings on the characteristics of interharmonics and can be useful for the development of interharmonic simulation programs.     

计及负频率影响的新能源发电低频间谐波检测方法

近年来,随着新能源发电的快速发展,越来越多的电力电子设备应用于发电单元,导致电网中出现了频率为次同步的间谐波。在对这类低频间谐波进行参数估计时,由于受负频率影响,现有的离散频谱校正方法存在较大的误差。为提高其频谱分析精度,文章在IEC 61000-4-7推荐的测量环境下,提出了一种计及负频率影响的离散频谱校正方法。根据信号FFT后的频谱特性,建立包含负频率在内的离散频谱校正模型;依据离散频谱的周期性,利用局部谱峰附近的4条谱线构建谱线方程组来求解低频间谐波的频率校正分量;根据估计出的频率,利用间谐波峰值谱线的频谱值及其共轭值来修正其幅值和相位参数。仿真结果表明,所提方法可以有效降低负频率成分对信号频谱谱线干涉的影响,提高低频间谐波的频率、幅值和相位校正精度,同时具有较好的抗噪性能。     

间谐波相序特性的研究

相序是三相电力系统中电压和电流的重要特性。为了认识间谐波的相序特性，文中以两种典型的间谐波源(变频驱动装置和电动机)为例，通过理论分析和实验探讨了它们产生的间谐波的相序。研究表明间谐波可以表现为正序或负序。但是间谐波的相序特性不同于谐波，同一频率的间谐波可以具有不同的相序。一般规律是：间谐波的相序与被调制的系统基波(或谐波)分量的相序相同。如果调制后得到的频率为负值，则间谐波信号的相序将变反，即由正序变负序或由负序变正序。文中的研究成果有助于深入认识间谐波的特性和发展间谐波仿真软件。     

A new method for measurement of harmonic groups in power systems using wavelet analysis in the IEC standard framework

The paper presents a new method based on the wavelet-packet transform for the analysis of harmonic groups in power systems, compatible with the standards of the International Electrotechnical Commission. The paper studies the performance of the new method in the analysis of harmonic groups and the spectral leakage associated with the presence of interharmonic components, synchronized and non-synchronized with the fundamental component, and also due to the loss of synchronization between the sampling window width and the fundamental frequency. Finally, the results obtained in the application of this method to different test waveforms are compared with the results obtained using the IEC method.     

Flicker produced by harmonics modulation

Flicker effect caused by voltage harmonics modulation is discussed. Simple functions are used to show that harmonic components, despite satisfying the specific harmonic limits, may produce flicker due to combined amplitude modulation (AM). Computer simulations, based on the International Electro-technical Commission (IEC) methodology, are numerically validated and then applied to calculate the instantaneous flicker sensation, resulting from different combinations of harmonics modulation. The results are also confirmed in laboratory tests using a flickermeter to measure the flicker levels obtained by synthesizing the same type of signals on a programmable function generator.     

Comparison of analog-to-digital filter conversion methods in a digital flickermeter

A standard of International Electrotechnical Commission (IEC) has defined the flicker measuring specification in an analog manner. But the analog specs are inefficient when implementing a flickermeter in the real world according to the standard. Therefore, it is necessary to convert its original analog filters to the corresponding digital forms as well as applying other digital processing techniques such as data sampling, bit resolution, and filtering theory. Even though a digital flickermeter may meet the requirements of the IEC standard, its outputs will vary according to the analog-to-digital filtering conversion methods used such as bilinear transformation, impulse invariance transformation, and covariance invariant transformation. This paper presents the characteristics of various filter conversion methods and the influences on the digital implementation of a flickermeter, which are simulated by using MATLAB^®. Finally, this paper concludes with which methods are the most adequate to implement an IEC digital flickermeter, helping ultimately to avoid ambiguities from analog prototypes described in original standard.     

基于IEC标准和全相位谱分析的谐波间谐波检测方法

IEC 61000-4-7:2002标准推荐的谐波间谐波测量新方法在同步采样下对非平稳信号具有良好的测量精度,但在非同步采样下测量精度较差,在各次谐波和间谐波相对相位变化下测量值会不同。为提高IEC新方法测量精度并保持测量值恒定,提出基于IEC新方法与全相位谱分析相结合的改进方法。该方法利用全相位谱分析具有优良的抑制频谱泄漏和相位不变性特点,实现在非同步采样下对多种典型非平稳信号谐波间谐波的精确测量,并与IEC新方法和传统加二阶余弦窗IEC新方法对比。仿真结果表明,所提出的改进方法非常适用于在非同步采样下谐波间谐波测量,即使各次谐波和间谐波相对相位出现变化,测量值仍然具有较高的精度并能保持恒定。     

基于FFT和HHT的Kaiser窗校正的风力发电机组电压闪变测量

由于电压闪变是非平稳信号,根据IEC闪变仪规范设计的闪变仪,在实际应用中无法直接进行频谱分析。提出了基于快速傅里叶变换(FFT)和希尔伯特黄变换(HHT)的Kaiser窗校正的风力发电机组电压闪变测量方法。分析了Kaiser窗的旁瓣特性和HHT的原理,通过Kaiser窗减少频谱泄露,利用FFT进行滤波,最后用HHT得到闪变包络。仿真实验结果表明,提出的算法可以测量出闪变发生的时间,并能有效克服单频闪变包络频率变化、多频率成分闪变包络频率变化、电网基波频率波动、谐波、间谐波及白噪声对检测结果的影响,其测量结果不仅稳定而且误差较小,还可以得到闪变发生的起止时间。实验进一步证明了该算法的有效性。     

IEC闪变仪对间谐波引起的电压闪变测量误差的分析

IEC推荐的闪变仪是以白炽灯的闪变问题作为测量分析的对象,由于荧光灯的闪变与白炽灯的闪变在机理方面有本质的不同,因而随着各种节能荧光灯型的大量使用,这种测量原理的局限性将随之显现出来。用频谱分析的方法分析了IEC推荐的闪变仪在测量间谐波引起的电压闪变方面的不足之处,进而引起大家对该问题的关注,以促进电压闪变测量原理和测量方法的进一步改进。     

闪变仿真法在电弧炉供电系统中的应用

为了仿真评估电弧炉引起的闪变严重度,对闪变仿真法及其在电弧炉供电系统中的应用进行了研究。先基于IEC闪变测量原理设计出闪变仪中各环节的传递函数和具体参数,再在SIMULINK环境下建立闪变仪模型并利用MATLAB语言编写专门的计算短时间闪变值Pst程序,根据IEC推荐的检验标准验证闪变仪模型的正确性和有效性,最后结合交流电弧炉随机模型,对电弧炉引起的闪变严重度进行仿真研究。研究表明运用仿真法评估电弧炉引起的闪变严重度是一种行之有效的方法。     

基于IEC标准的闪变测试系统研究

讨论了国际电工委员会(IEC)闪变测量原理，分析了滤波器参数对系统的影响。将IEC给出的滤波器进行双线性变换得到相应的IIR数字滤波器，给出了数字实现的方法。对短时间闪变值的统计计算方法进行了分析，给出了减小误差的方法。依据IEC推荐的闪变测试仪功能和设计规范，设计了闪变测试系统，软件基于LabWindows/CVI虚拟仪器开发平台。经测试该系统性能指标完全满足IEC没计规范的要求。     

基于FFT和小波变换的交直流并联输电系统间谐波研究

运用谐波调制理论,结合开关函数的傅里叶分析,研究了在交直流并联输电系统下,交流系统供电电源含有畸变谐波时,直流线路和交流侧都产生间谐波的机理。给出了整流侧直流电压、直流电流以及交流电流产生的间谐波的一般形式。经过小波变换除去信号中的非稳态分量以后,再使用加窗快速傅里叶变换可以很好地得出其中的稳态分量。通过一个典型交直流并联输电系统数字仿真,同时在供电电源含有畸变谐波的情况下,对交直流系统的电压和电流量进行了间谐波计算。利用傅里叶小波分析综合分析法得到的仿真结果和计算结果相比较,验证了间谐波产生机理的正确性和有效性。     

Desynchronized Processing technique for Harmonic and interharmonic analysis

A new desynchronized processing technique for harmonic and interharmonic analysis that has general validity and results fully compatible with the IEC standard is presented. This technique is based on a double-stage signal processing procedure: In the first stage, the harmonic components are accurately estimated via interpolations in frequency domain and filtered away from the original signal so that in the second stage, interharmonics can be evaluated without the spectral leakage due to harmonic tones. Since the procedure does not require synchronization, it allows adopting a fixed sampling frequency and, at the same time, the direct use of fast Fourier transform on the acquired samples, thereby reducing the computational burden. The procedure is successfully applied to both numerical tests and onfield measurements. The obtained results are as accurate as those of synchronized techniques.     

基于频谱分析的间谐波闪变效应计算

在分析IEC闪变仪测量原理的基础上,提出一种基于频谱分析的电压闪变计算方法,先利用快速傅里叶变换（FFT）进行频谱分析,得到各频率分量的参数,然后利用这些参数计算电压闪变。新算法不仅能计算调制波和间谐波引起的总瞬时闪变视感度,还能计算出每个间谐波或间谐波对引起的瞬时闪变视感度占总瞬时闪变视感度的比例,即对闪变的贡献。它表明调制波是间谐波的特例,并且,当输入电压中含有间谐波对时,间谐波对引起的瞬时闪变视感度中的共同作用部分与基波和间谐波的初相角有关,而在以往的研究中一般未考虑相角的影响,或将相角默认为0°。仿真算例将频谱法和IEC算法进行了对比分析,验证了频谱法的有效性和准确性。     

电压闪变仪的软件设计及其应用

电压闪变是评定电能质量的重要指标之一,准确检测电压闪变具有重要的意义。根据国际电工委员会(IEC)制定的闪变仪设计规则,将闪变仪的模拟模型转化为数字模型,然后基于COM技术结合VC 编程,完成了数字式闪变仪软件的设计。文中设计的闪变仪软件达到了IEC标准的要求,而且已应用于电气化铁道电压闪变的检测,收到了良好的效果。     

Interharmonics analysis of power signals with fundamental frequency deviation using Kalman filtering

In this paper a spectral decomposition-based method for interharmonic computation is proposed for power systems where the fundamental frequency fluctuates significantly. In the proposed method, the frequency domain components of the voltage waveform are obtained by Kalman filtering. Both the system fundamental frequency and the correct spectrum of the voltage waveform, and hence the exact interharmonics are obtained. The proposed method is tested with both simulated and field data obtained from different electric arc furnace (EAF) plants, where the system frequency deviates continuously due to the fluctuating load demands. Since the interharmonic frequencies are obtained by using Kalman filtering, no leakage effect of the DFT-based methods is involved in case of frequency deviations, which is an important advantage of the proposed method.