谐波与电能计量

文章对谐波的产生和谐波对电力系统危害作了简单的介绍,并通过普通电子式多功能电能表和基波电子式多功能电能表电能计量的对比,阐述了谐波对电能计量的影响,并对这两种电能表的测量方式做了详细的分析,最后提出推广基波电能表的可行性。     

准同步采样在电力系统频率、频偏和相位差测量中的应用

本文介绍测量电网频率、频偏和相位差的准同步采样方法。它能有效地抑制谐波对测量结果的影响和减小未完全同步所产生的误差,从而使上述参数的采样数字式测量具有很高的准确度,为电力系统提供了一种快速可靠的测量方法。     

基于场强法的高压线路谐波检测仪的研究与设计

为了对高压输电线路电压谐波含量进行直接测量,及时了解输电线路谐波情况,本文提出了一种基于场强法测量高压线路电压谐波信号的新方法,克服了传统测量方法不能获得高压线路电压谐波信号问题。通过建立场强法获得电压信号的数学模型,并从理论上证明了其正确性;同时设计了谐波检测仪实际测量电路,包括数据采集器和数据接收器,二者之间通过无线发送数据,解决了高低压隔离问题,高压输电线路谐波检测仪可以方便地检测出高压线路上电压的谐波含量。     

基于iP-iQ理论的谐波影响下电能计量改进方法研究

电力电子设备随其在电力系统的广泛应用,已成为电网中主要的谐波源,其危害性早已引起了国内外的广泛关注,尤其是谐波影响下电能计量问题一直是计量领域的焦点和难题。文章基于iP -iQ 理论提出一种改进谐波电流检测方法,能够快速、准确地区分基波和谐波参数,从而实现基波电能和谐波电能的分别计量,通过仿真与实验结果验证了所提出方法的有效性。     

电磁式电压互感器谐波误差测量方法研究

为实现电磁式电压互感器在基波叠加谐波的实际波形下的计量误差测试,提出一种基于有源电子分压器的测量电磁式电压互感器谐波计量特性测量方法.以有源电容式分压器作为宽频比例标准装置,采用误差反馈技术,提高互感器二次转换单元测量准确度,基于LabVIEW和高精度数字化仪完成信号的测量和误差的计算,完成对4台电磁式电压互感器进行谐...     

电力参数间谐波测量算法的研究

DFT的泄漏和栅栏效应不能测量电力系统的间谐波和分析电力系统谐波误差。一般通过加窗插值DFT能测量间谐波,然而需要构造窗函数使得分析及实际运行变得复杂。本文通过简单的频域变换结合多谱线插值并且给出了一种相应的算法,仿真结果表明该方法运行简单便于分析,精度高,因此为电力系统谐波分析提供了一种满意的工具。     

基于小波变换的介损测量方法研究

高压介质损耗测量是电力系统中检测高压电气设备的常规项目，对于高压电气设备的正常运行至关重要。依据小波分析理论、阐述了信号分解重构的过程，并且结合损耗测量中的波形特征，提出了利用小波变换来提取基波信号计算介质损耗角的检测方法，能够有效的消除谐波和噪声的影响。仿真分析表明，小波变换在介损测量中有较好的应用效果。     

基于小波变换的电力系统谐波测量方法

小波变换具有时-频局部化特性,在电力系统的分析中具有无比广阔的应用前景.本文将小波变换方法应用于电力系统谐波检测中,并提出了同步检测与小波变换相结合的电压闪变测量方法,仿真结果表明此方法适用于电压闪变信号的检测和分析.     

接收机测量谐波的方法及优缺点分析

本文提出了一种采用测量接收机HP8902A测量射频信号源谐波的方法,对该方法的特点及应用范围进行了分析与说明,并通过与常规的频谱分析仪测量谐波的方法进行比较,确定了该测量方法的可行性,可以用于没有频谱分析仪的情况下射频信源谐波的检定。     

变频空调缺陷：引起电网谐波污染及其危害

目前市场中采用交流变频技术的家用空调的核心是变频器，变频器就是电网中的非线性负载，其运行过程中工频电源整流成直流电压信号，经电容滤波及大功率晶体管开关元件逆变为频率可变的交流信号。在整流电路中，输入电流的波形为不规则的矩形波，波形按傅立叶级数分解为基波和各次谐波，其中的高次谐波将干扰输入供电系统。输出回路电流信号也可分解为只含正弦波的基波和其它各次谐波，谐波与电力系统中基波叠加，造成波形畸变从而引起电网谐波污染。     

Measurement uncertainty and temporal resolution of Doppler global velocimetry using laser frequency modulation

A Doppler global velocimetry (DGV) measurement technique with a sinusoidal laser frequency modulation is presented for measuring velocity fields in fluid flows. A cesium absorption cell is used for the conversion of the Doppler shift frequency into a change in light intensity, which can be measured by a fiber coupled avalanche photo diode array. Because of a harmonic analysis of the detector element signals, no errors due to detector offset drifts occur and no reference detector array is necessary for measuring the scattered light power. Hence, large errors such as image misalignment errors and beam split errors are eliminated. Furthermore, the measurement system is also capable of achieving high measurement rates up to the modulation frequency (100 kHz) and thus opens new perspectives to multiple point investigations of instationary flows, e.g., for turbulence analysis. A fundamental measurement uncertainty analysis based on the theory of Cramér and Rao is given and validated by experimental results. The current relation between time resolution and measurement uncertainty, as well as further optimization strategies, are discussed.     

功率流测量以及振动能量参数估计试验研究

本文搭建了功率流测量以及能量参数估计试验平台,分析了功率流不同计算方法对功率流传递规律的影响,建立了功率流和振动能量参数间的关系。通过在振源和接受体之间插入阻抗头传感器,获得同点同方向的力和加速度信号,分别应用时域平均法、基波频域法和二次谐波频域法计算功率流。研究表明当激振频率为各阶模态频率分倍频时,其谐波振动需要加以控制。负功率流是功率流测量中不可避免的现象,本文从多自由度振动的角度揭示负功率流的成因。针对能量参数难以测量的难题,分别运用驱动点阻抗和导纳法估计振动能量,并通过系统损耗因子验证了功率流和能量参数间的关系。     

Autocorrelation measurements of bursts of picosecond pulses

In a master oscillator power amplifier system a powerful train of pulses can be generated. A simple method is described to measure the duration of these pulses. The measurements have been performed both at the fundamental frequency (1053 nm) and at the second harmonic (527 nm). In accordance with theoretical expectations we have observed a narrowing of the pulse owing to frequency doubling.     

谐波信号的闭环检测和估计算法及其应用

从联合检测估计的角度讨论了检测器和估计器之间的耦合机制,并就水声目标线谱特征提取问题研究了一种谐波信号的闭环检测和估计算法.该算法通过迭代形式在检测器和估计器之间不断交换信息,用以改善未知参数的先验分布,从而得到较好的检测和估计性能.对海试数据的仿真结果表明,该算法可以有效地提取目标的线谱特征.     

Analog-to-digital conversion and harmonic noises due to theintegral nonlinearity

Analog-to-digital conversion inherently introduces unwanted harmonic noises due to the nonlinear transfer function error. It is essential to set proper models of the noise generation mechanisms, to quantify and compare the analytic performance of the high-resolution measurement systems including analog-to-digital converter (ADC). We addressed the importance of the integral nonlinearity in the analysis of the ADC system. We modeled the nonlinearity via a linear combination of simple power functions with single parameters and calculated the magnitudes of the harmonic noises generated by the sigmoidal shape of the ADC transfer function, analytically and numerically. For a typical ADC, a model x^(1+ν)+μx² was reasonably adopted, which produced the most significant harmonic noises at the second-and the third-order multiples of the fundamental frequency. Practical examples of the high-resolution ADC were observed, and demonstrated to show that the simple model explains the harmonic noises     

Intravascular ultrasound tissue harmonic imaging in vivo

Tissue harmonic imaging (THI) has been shown to increase image quality of medical ultrasound in the frequency range from 2 to 10 MHz and might, therefore, also be used to improve image quality in intravascular ultrasound (IVUS). In this study we constructed a prototype IVUS system that could operate in both fundamental frequency and second harmonic imaging modes. This system uses a conventional, continuously rotating, single-element IVUS catheter and was operated in fundamental 20 MHz, fundamental 40 MHz, and harmonic 40 MHz modes (transmit 20 MHz, receive 40 MHz). Hydrophone beam characterization measurements demonstrated the build-up of a second harmonic signal as a function of increasing pressure. Imaging experiments were conducted in both a tissue-mimicking phantom and in an atherosclerotic animal model in vivo. Acquisitions of fundamental 20 and 40 MHz and second harmonic acquisitions resulted in cross sections of the phantom and a rabbit aorta. The harmonic results of the imaging experiments showed the feasibility of intravascular THI with a conventional IVUS catheter both in a phantom and in vivo. The harmonic acquisitions also showed the potential of THI to reduce image artifacts compared to fundamental imaging.     

Multiharmonic generators for relative phase calibration ofnonlinear network analyzers

Multiharmonic generators are of interest for determining coupler phase dispersion of nonlinear network analyzers inherently dealing with nonsinusoidal waveforms for RF current-voltage (I-V) measurements. Supported by simple waveform analysis, two on-wafer devices are experimentally evaluated: a single diode and a nonlinear transmission line (NLTL). The investigation uses an active harmonic load-pull system with 2 GHz fundamental frequency. It turns out that the NLTL is well suited as a reference generator. We present measurement examples of phase dispersion for different directional couplers up to 18 GHz and the application to RF I-V waveforms of a 1-W power HBT with harmonic load tuning     

A Simple Method for Design of Adaptive Filters for Sinusoidal Signals

Filtering of input signals in algorithms for measurement of power system electrical parameters is very important. Filters are used to minimize the noise effect and eliminate the presence of higher order harmonics. In addition to that, a number of measurement algorithms apply orthogonal signal components obtained by two orthogonal finite-impulse response filters. The frequency response of the filters must have nulls at the higher order harmonic frequencies that are expected to be present in the signal and must have a unity gain at the main harmonic frequency. In the case of a time-varying frequency, the filter parameters have to be adapted during frequency estimation. In this paper, a simple method for online design of digital filters for sinusoidal signals is proposed. It is based on closed-form solutions for calculating filter coefficients. A simple linear algorithm for frequency estimation was used, and a derived algorithm for online adaptation of the filter coefficients is computationally very efficient. The number of subsections in the cascade and data window lengths can also be changed, depending on the frequency variations during measurement.      

A new filter-bank configuration for harmonic measurement

In this paper a new adaptive filter-bank structure suitable for the accurate harmonic measurement in power supply systems is presented. This adaptive measurement technique is based on the resonator-in-a-loop filter-bank structure and includes a new modified Gauss-Newton gradient algorithm. Using this filter-bank structure and a least-squared-error approximation method, simulation results are presented to establish the performance of the technique. The effects of time-varying fundamental frequency are also investigated using this filter-bank structure. Simulation results show that the fundamental frequency can be tracked with very small error. The technique is also successfully applied to a measured voltage signal sampled from the mains to demonstrate performance     

Two-dimensional weak-object transfer functions in the scanning harmonic microscope

Abstract

The two-dimensional imaging properties of scanning harmonic microscopes are considered. The two-dimensional weak-object transfer functions for non-confocal (point source and large-area incoherent detector) and confocal (point source and point detector) scanning harmonic microscopes are calculated. Results show that the harmonic microscopes are capable of super-resolution in that the spatial frequency cut-off is twice that for a microscope working at the fundamental wavelength. Confocal scanning harmonic microscopes exhibit better resolution than the conventional type.