基于稀疏表示的电力系统谐波信号频率分析

谐波污染对电力系统和电力设备产生严重的危害和影响,当电力信号中存在强大的噪声成分时,传统的快速傅里叶变换(fast fourier transform,FFT)无法准确提取出谐波成分。该文在信号稀疏表示理论的基础上,提出基于稀疏表示的电力系统谐波信号频率分析方法,并设计出谐波频率分析快速算法。通过Matlab仿真,结果表明该方法能准确提取谐波成分的频率,具有较强的抗噪能力。     

Operational method of measuring the parameters of a harmonic signal

A method of measuring the parameters of a harmonic signal containing a constant an slowly varying component is proposed and investigated. The method has optimum interference proctection. Expressions are obtained for the algorithms for processing the input signal in analog and digital versions, an estimate of the errors in measuring the parameters is given, and the principle for constructing a digital microprocessor measuring instrument is described. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 47–51, July, 1995.     

瞬频特征的谐波小波域提取与应用

为了能精确提取出复杂信号中特征分量的瞬频特征,提出了谐波小波域内的分量瞬频估计方法。该方法首先在分析谐波小波变换的基本原理及其优良特性的基础上,对谐波小波进行加窗光滑处理,改善了谐波小波的时域衰减特性。然后,针对在传统瞬频估计方法的不足之处,将线性回归、自适应滤波、曲线平滑、重采样等方法应用到瞬时相位函数的处理中,提高了瞬时频率特征的提取精度。最后,通过仿真实验与工程实践验证了该方法在信号分量瞬频特征提取中的可行性与有效性。     

植物微弱电波信号的时、频域分析

在时域和频域上对植物电波信号进行了分析.植物电波信号的幅值处于μV级量级,是一种微弱信号;随时间变化剧烈,在不同时刻的取值关系松散;植物电波信号属于低频信号,其功率谱主要分布在小于5 Hz这一频段.     

Multi-user interference cancellation technology in the presence of multiple frequency offsets

The performance of multi-user detectors in the presence of multiple frequency offsets under a Rayleigh fading channel environment is analysed, and techniques to estimate and remove multiple frequency offsets (FOs) for successive interference cancellation (SIC) and parallel interference cancellation (PIC) receivers are also proposed. The closed form expressions derived for bit error rate (BER) of SIC and PIC schemes in the presence of multiple FOs have been verified using extensive simulation results. The PIC is shown to be less sensitive to frequency offsets as compared to SIC. It is demonstrated through analytical and simulation results that the proposed frequency offset estimation and correction techniques provide approximately 8 dB gain in the BER performance over conventional SIC and PIC schemes in the presence of multiple frequency offsets     

Method of measuring signal parameters in the presence of nonstationary noise

A method, based on the maximum optimum maximum likelihood criterion, of measuring the parameters of signals containing quasi-deterministic and random noise is investigated. Translated from Izmeritel'naya Tekhnika, No. 4, pp. 42–47, April, 1997.     

Estimation of composite signal parameters in coherent optical systems

Translated from Izmeritel'naya Tekhnika, No. 10, pp. 14–16, October, 1989.     

Random multiaxial fatigue: A comparative analysis among selected frequency and time domain fatigue evaluation methods

Fatigue analysis of mechanical components subjected to random loads has been recently upgraded through several developments of calculation procedures, with the scope to support the designer within the loading condition numerical simulation. Under such scenario, the frequency domain approach is characterized by interesting features, which support its adoption in alternative or in conjunction with the classic time-domain approach, especially when the frequency domain is applied for the individuation of the component critical locations. The major goal of this paper consists of an overview about the strength and weaknesses of frequency approach with respect to the time domain one by comparing the reference time domain methods with their frequency domain translation. A significant test case development will be shown, representing a classic automotive one (chassis validation). Promising results of the frequency method application will be presented, encouraging its adoption on large scale.     

Estimation of mixing parameters for cancellation of discretized eddy current signals using time and frequency domain techniques

In this paper, we present two methods for estimating the mixing parameters used in scaling, rotating, and time shifting discrete time eddy current impedance plane trajectories in order to suppress unwanted support plate signals. One method operates directly on the time signals. The other method operates on the frequency domain representation of these signals and consequently is computationally more involved. Both methods require the minimization of a functional which measures the energy difference between the horizontal and vertical components of the high and low frequency data. Three illustrative examples are presented, and it is shown that the use of the frequency domain method is justified if the data are corrupted with random noise as well as with unknown multisample time shifts.     

Estimation of laser beam pointing parameters in the presence of atmospheric turbulence

The problem of estimating mechanical boresight and jitter performance of a laser pointing system in the presence of atmospheric turbulence is considered. A novel estimator based on maximizing an average probability density function (pdf) of the received signal is presented. The proposed estimator uses a Gaussian far-field mean irradiance profile, and the irradiance pdf is assumed to be lognormal. The estimates are obtained using a sequence of return signal values from the intended target. Alternatively, one can think of the estimates being made by a cooperative target using the received signal samples directly. The estimator does not require sample-to-sample atmospheric turbulence parameter information. The approach is evaluated using wave optics simulation for both weak and strong turbulence conditions. Our results show that very good boresight and jitter estimation performance can be obtained under the weak turbulence regime. We also propose a novel technique to include the effect of very low received intensity values that cannot be measured well by the receiving device. The proposed technique provides significant improvement over a conventional approach where such samples are simply ignored. Since our method is derived from the lognormal irradiance pdf, the performance under strong turbulence is degraded. However, the ideas can be extended with appropriate pdf models to obtain more accurate results under strong turbulence conditions.     

大信号网络分析中的包络域

超越S参数的大信号网络分析是解决非线性问题的一个行之有效的方法,包络域是该分析法的一个重要概念,是指能同时表征载波基波和载波各高次谐波的包络的一种方法,它充分而形象地表征了系统的非线性特性.作者从基本原理出发详细分析了包络域的概念.     

Fourier analysis of harmonic frequency transmission dielectric structures

We use an analytical calculation based on the Fourier-transform method to study the transmission spectra of multilayer dielectric optical structures as a function of the relative widths of the layers that constitute the unit cell. We can select which harmonics of the fundamental design frequency are transmitted. The results of this Fourier-transform approach are compared with the exact transmission calculated by means of the transfer matrix method and provide a more intuitive understanding of the transmission spectrum. A simple phasor diagram is derived from this Fourier-transform analysis for this purpose. Inasmuch as it is difficult for us to perform experiments in the optical region, we fabricate rf analogs of these structures, using coaxial cables that have different impedances. Experimental results agree with theory.     

扬声器低频谐波失真的数值分析

扬声器作为一种非线性振动系统，在低频段仅考虑力学恢复力非线性可用经典的Duffing方程来描述；同时考虑恢复力和磁场非线性可用广义的Duffing方程来表征。Yoshinisa研究了仅含恢复力非线性扬声器低频非线性现象中的低频谐波失真现象，但对恢复力和磁场非线性同时存在的扬声器低频谐波失真问题未作研究。西方利用Matlab软件求解扬声器非线性振动系统的广义Duffing方程的数值解，又利用Spectra Plus频谱分析软件得到扬声器低频谐波失真与频率的关系曲线，通过分析低频谐波失真与频率的关系曲线，并着重讨论磁场的非线性对扬声器低频谐波失真的影响，得出一些有价值的结论。     

Coupled finite-element/boundary-element analysis of a reciprocating self-excited induction Generator in a harmonic domain

This paper suggests a general method for analysis of a reciprocating self-excited induction generator based on the coupled finite-element/boundary-element method in a harmonic domain. The finite-element method is used for iron and copper parts in order to deal with nonlinearity and eddy currents, while the boundary-element method is utilized for the air-gap region between the moving parts using a free-space Green function that facilitates the application of a linear time periodic movement. The proposed method leads to a static global matrix that is symmetrical for particular boundary conditions. The results agree well with those obtained by the time-stepping methods.     

Electromagnetic optimisation using sensitivity analysis in the frequency domain

Gradient-based optimisation relies on the response Jacobian whose evaluation constitutes a major computational overhead in full-wave numerical analysis. Adjoint-based techniques may offer numerically efficient solutions, but their implementation is too involved in the case of full-wave computations. A simple approach that uses the self-adjoint sensitivity analysis and Broyden's update is proposed. The overhead of the Jacobian computation is greatly reduced because an adjoint system analysis is not needed and because Broyden's update is used to compute the system matrix derivatives. To improve the robustness of the Broyden update in the sensitivity analysis, we propose a switching criterion between the Broyden and the finite-difference estimation of the system matrix derivatives. We illustrate and validate the proposed method using full-wave commercial electromagnetic solvers based on the finite-element method as well as on the method of moments. Different gradient-based optimisation algorithms are exploited in the examples where efficiency is compared in terms of CPU time savings.     

Application of frequency domain analysis in the testing of packages

The sine sweep is a standard method of excitation used experimentally to evaluate the transmissibility characteristics of a package/product. This paper critically analyses this method, points out potential sources of error and shows the advantages of frequency domain analysis. The measurement of transmissibility of packages/products as the frequency response function (FRF) from auto- and cross-spectra is demonstrated. Two ways of broadband excitation are investigated, namely white noise and impulse excitation.     

分数傅里叶变换域的调频信号稀疏性研究

调频信号广泛应用于声纳、雷达、激光和新兴光学交叉研究领域,其紧致性(稀疏性)是调频信号采样、去噪、压缩等研究中面临的共性基础问题。本文致力于研究调频信号在分数傅里叶变换域的稀疏性,提出了一种最大奇异值法来估计调频信号的紧致分数傅里叶变换域。该方法利用调频信号幅度谱的最大奇异值来度量其紧致域,并应用鲸鱼优化算法来搜寻紧致域,有效改善了现有方法的不足。与MNM和MACF方法相比,本文方法给出了调频信号在分数傅里叶变换域更加稀疏的表征,具有更少的重要振幅数。最后,给出了该方法在调频信号滤波中的初步应用。