Quantities extracted from space-charge measurements as markers for insulation aging

The relation of space charge-derived quantities with aging stresses and time is discussed in this paper. Polyethylene-based materials, aged for different times under electrical and/or thermal stress, are subjected to space charge measurements. Quantities are derived, that is, the threshold for space charge accumulation and the apparent, trap-controlled mobility, obtained by the threshold and the depolarisation characteristics, respectively, which show time variations depending on the level of applied stress and aging time, i.e. on the extent of degradation. This indicates that such quantities can be considered as aging markers useful for the diagnosis of bulk degradation in insulation systems aged under electrical field, dc or ac, and temperature.     

A method for estimation of insulation residual operation capability of electrical equipment

A mathematical model of partial discharge evolution during aging of the dielectric is presented. Experimental data on variation of partial discharge intensity in time are interpreted using the model. This allows for estimation of the residual capability of dielectric use.     

一种基于非线性模型的OFDM信道估计

导频辅助的信道估计方法是OFDM系统中应用最为广泛的一类信道估计方法,其中的2-D维纳滤波是最小均方误差意义下的最佳线性估计器,但是由于其计算量非常大,因而在实际中不能得到很好的应用。2×1-D的维纳滤波器利用信道相关函数的可分离性,对2-D维纳滤波器进行了简化,一定程度地降低了其复杂性,但仍然需要知道或估计信道的统计特性。文中介绍了一种基于非线性模型的信道估计方法,对其算法进行了仿真并与2×1-D维纳滤波的误比特率(BER)性能进行了比较。仿真结果表明,此方法能以较低的复杂性达到与2×1-D维纳滤波相近的性能,且无需对信道特性估计,是一种较实用的信道估计方法。     

一种变频变压的双频注入绝缘监测方法

核反应堆电加热工程环境下的高温、大电流、加热损耗导致的单相绝缘故障是IT系统的主要故障形式,本文分析发生单相绝缘故障的两种情形:①故障支路绝缘电阻偏大时导致总注入源回路电流偏小;②故障支路分布电容过大导致支路阻性电流偏小.基于这两种情形产生的误差,本文总结双频法检测绝缘电阻的基本原理,并在利用双相锁相放大技术提取微弱信...     

A frequency response estimation method based on smoothing and thresholding

A standard approach for estimating the frequency function of a linear dynamical system is to use spectral estimation. Traditionally, this is done by smoothing the noisy frequency data using linear filters. The method has proved to be successful in most cases and is widely used. However, if the frequency response has fine details appearing only locally in frequency, the loss of resolution caused by smoothing might result in unacceptable errors. In this paper, a different method for frequency response estimation is suggested. The method utilizes recently proposed wavelet-based denoising schemes combined with traditional smoothing techniques. The wavelet transform is applied in the frequency domain in order to provide a suitable frequency window. Tested through simulations, this approach provides an alternative when traditional methods fail. © 1998 John Wiley & Sons, Ltd.     

A method for the design of MRI radiofrequency coils based on triangular and pulse basis functions

This paper presents a numerical technique for the design of an RF coil for asymmetric magnetic resonance imaging (MRI) systems. The formulation is based on an inverse approach where the cylindrical surface currents are expressed in terms of a combination of sub-domain basis functions: triangular and pulse functions. With the homogeneous transverse magnetic field specified in a spherical region, a functional method is applied to obtain the unknown current coefficients. The current distribution is then transformed to a conductor pattern by use of a stream function technique. Preliminary MR images acquired using a prototype RF coil are presented and validate the design method.     

A method for the design of MRI radiofrequency coils based on triangular and pulse basis functions.

This paper presents a numerical technique for the design of an RF coil for asymmetric magnetic resonance imaging (MRI) systems. The formulation is based on an inverse approach where the cylindrical surface currents are expressed in terms of a combination of sub-domain basis functions: triangular and pulse functions. With the homogeneous transverse magnetic field specified in a spherical region, a functional method is applied to obtain the unknown current coefficients. The current distribution is then transformed to a conductor pattern by use of a stream function technique. Preliminary MR images acquired using a prototype RF coil are presented and validate the design method.     

基于分块雅可比矩阵的最小二乘状态估计算法

提出了一种基于分块雅可比矩阵的加权最小二乘状态估计算法.该方法将全部的注入功率量测、赋予很大权值的虚拟量测和必要的支路量测来构造一组恰好可求解系统全部状态变量的量测集,将余下的支路功率量测作为量测系统的冗余部分看待,并依此对量测雅可比矩阵进行分块,在此基础上推导出了该文算法迭代的修正方程式.该文所提算法既具有很好的数值稳定性,又能够减少计算量.仿真试验表明该方法是快速且数值稳定.     

基于CZT的电力谐波参数高精度估计

提出了一种基于CZT的电力系统谐波参数高精度估计方法.利用CZT实现频谱细化的特点,首先从复杂信号中提取基波分量,将其减去.然后对剩余信号加5项Rife-Vincent窗,进行FFT分析.最后根据提取基波频率求出各次谐波频率,对Rife-Vincent窗函数在频域插值.仿真验证表明5项Rife-Vincent窗抑制频谱泄露效果很好,在非同步采样的情况下,对含有30次谐波的复杂信号进行仿真分析,结果与传统双谱线插值算法有几乎相同的估计精度,但计算时间约节省了一半.     

Theory and application of dynamic aging for life estimation inmachine insulation

After a brief discussion on possible on-line indicators of aging, this paper presents a concept of dynamic aging theory (DAT). Based on the philosophy of a DAT, a dynamic multistress aging model is proposed. Necessary DAT formulation and software have been developed for testing the model against laboratory aging data. In this study, dynamic stagnation voltage (DSV), a derived partial discharge parameter, and the groundwall insulation response to a traveling acoustic wave have been found to be the most appropriate parameters for assessment of remaining insulation machine life. This approach is shown to be a meaningful and practical solution to a very complex problem. Although this study is in its initial stage, it does show significant promise as an on-line tool for dynamically predicting remaining life based on DAT and other appropriate feedback measures     

基于复合EKF算法的锂电池组的SOC估计

动力锂电池组的荷电状态SOC估计是电动汽车能量控制的重要参数。针对串联锂电池组的SOC估计问题,利用扩展卡尔曼滤波法(EKF)和传统的安时积分法相结合(复合EKF算法)优势互补,并运用对于扩展卡尔滤波法较准确地估计电池的Thevenin模型,以电池组的最小单体电池的电压作为参考电压值,用提出的算法结合所选用的电池模型,对模拟电动车的实际工况进行电池组放电实验,证明这种复合算法不但比EKF法估计SOC准确,对误差还有一定的修正能力,而且还能满足电动车SOC准确度的需要。     

A method for experimental determination of defectiveness in the insulation system of induction motor windings taking into account different mechanisms of the production of defects

The existing methods for determining the defectiveness in the winding insulation during the run-in period are analyzed. The methods based on testing the breakdown of the insulation extracted from slots of unimpregnated stators are considered. A method for experimental determination of defectiveness in the insulation systems of impregnated windings of induction motors is proposed. This method takes into account different mechanisms of the production of flaws. A design of the winding models for conducting accelerated tests is developed.     

基于MUSIC的含噪声信号频率估计

频率估计是数字信号处理的重要内容,特别是对含有高斯白噪声的信号进行频率估计一直是信号处理的经典课题。频率估计不仅在理论上,而且在实际应中,都有非常重要的研究价值。本文采用空间谱估计的典型代表MUSIC算法,对含高斯白噪声的信号进行频率估计,同时也通过MATLAB软件对其进行了仿真。仿真结果表明对单、多个含噪声的正弦信号而言,MUSIC算法有良好的频率特性,并能达到预期效果。     

融合RGB特征和Depth特征的3D目标识别方法

针对目标类内差异、类间相似的识别问题,结合RGB图像和Depth图像各自的优势,提出一种基于多核学习的融合RGB特征和Depth特征的3D目标识别方法。该方法提取目标物体的RGB特征和Depth特征;并根据两种特征的类内、类间相似性均值和方差,为特征自适应的分配不同的权重;最后利用多核学习(MKL)的方法对特征进行加权融合,并结合SVM分类器,实现3D目标识别。最后通过在Kinect相机得到的RGB-D数据集上进行实验,验证了该文方法能够有效地实现对RGB特征和Depth特征的融合,很好的解决类内差异、类间相似的3D目标识别问题,提高了3D目标识别的识别率。     

A new mapping method for phase estimation of single‐phase signals: A new generalization and new realizations of the DFT estimation method

This paper proposes and analyzes a new simple real‐time phase‐estimation method for single‐phase signals, which is based on a vector mapping theory of n‐dimensional to 2‐dimensional vectors. According to the analyses, the proposed mapping method can estimate instantly and properly the true phase of the signals that are contaminated by significant amplitude of noise and harmonics. The mapping method contains the conventional DFT method as a special case. In other words, it can be treated as a generalization of the DFT. Several simple realizations of the mapping method are also newly proposed as a single‐input and two‐output digital mapping filter in both nonrecursive and recursive forms. The recursive realization being able to decrease drastically computing load utilizes the normal form that is robust to finite word length effects. As an application of the proposed mapping method, inverter‐using power control system connected with a single‐phase grid is shown. All analytical results are verified by numerical experiments and the usefulness of the newly proposed mapping method is confirmed. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(1): 27–38, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20263     

Mathematical and experimental analysis of the field drying of powertransformer insulation

A mathematical model was developed to predict the adsorption and diffusion of moisture by oil-impregnated transformer insulation during field installation and the diffusion, desorption and evaporation of moisture during vacuum drying practices. A field drying experiment was performed on a new 93 MVA power transformer to verify the accuracy of the drying model. Four paper models were inserted in the transformer during manufacture to monitor, the course of moisture diffusion during the study. Insulation temperatures were also monitored to evaluate a hot oil spray process in uniformly heating the transformer insulation. Good agreement was achieved between mathematical predictions and field moisture measurements. High temperature processes are essential to the rapid removal of moisture during field vacuum drying operations     

一种基于改进网格搜索和广义回归神经网络的锂离子电池健康状态估计方法

为了准确估计锂离子电池的健康状态,本文提出一种新的基于改进网格搜索(GS)和广义回归神经网络(GRNN)的估计方法.首先,对集中的数据进行处理,并通过相关性分析方法,提取有效的特征数据,包括电压、电流等.其次,提出一种基于改进网格搜索和广义回归神经网络的回归模型来估计电池的健康状态.最后,使用两个锂离子电池公共数据集验...     

A new experimental application of least-squares techniques for the estimation of the induction motor parameters

This paper deals with a new experimental approach to the parameter estimation of induction motors with least-squares techniques. In particular, it exploits the robustness of total least-squares (TLS) techniques in noisy environments by using a new neuron, the TLS EXIN, which is easily implemented online. After showing that ordinary least-squares (OLS) algorithms, classically employed in the literature, are quite unreliable in the presence of noisy measurements, which is not the case for TLS, the TLS EXIN neuron is applied numerically and experimentally for retrieving the parameters of an induction motor by means of a test bench. Additionally, for the case of very noisy data, a refinement of the TLS estimation has been obtained by the application of a constrained optimization algorithm which explicitly takes into account the relationships among the K-parameters. The strength of this approach and the enhancement obtained is fully demonstrated first numerically and then verified experimentally.     

A practical, precise method for frequency tracking and phasor estimation

Comprehensive analysis of discrete Fourier transform (DFT) error is given in this paper, including why it is accurate when used in the case of synchronous sampling and how error rises when sampling frequency does not synchronized to signal frequency. Simple but precise expressions of phase angle error and amplitude error are given. Practical formulas to calculate the true phase angle and amplitude are presented. The formulas are very simple and precise. Based on the formula to calculate true phase angle, a new frequency tracking method is developed. The proposed method can be calculated recursively. And, with notable accuracy improvement, the calculation burden is little more than the traditional DFT method. Also, an adaptive method to suppress the effect of harmonics is presented, which adds very little calculation burden with satisfying performance. The most distinguished feature of the proposed method is that it is not only precise, but also simple. Some examples are given to demonstrate the feasibility, precision, simpleness and robustness of the proposed method.