基于小波变换的非线性负载畸变电能计量研究

随着大量冲击性载荷接入电网,电网低压侧信号出现非正弦畸变,严重威胁电网稳定运行。传统电能表多基于正弦信号进行计量,畸变信号会导致漏计大量电能,给电网带来经济损失。基于国内外研究进展,建立了电网信号数学模型,分析了畸变信号下功率的组成成分。采用提升小波变换算法对畸变信号进行处理,验证了db4小波电能计量方法的准确性。研究表明:相比较于快速傅里叶变换和第一代小波变换,db4提升小波变换的基波功率值更接近于理论值。     

一种基于瞬时频率的多普勒畸变声信号校正方法

运动声源信号中广泛存在多普勒效应影响,针对其引起的频移、频带扩展问题提出了一种校正方法。信号的频率非平稳性的还原通常使用重采样方法,而建立一组重采样时间序列就是该方法的核心。对于多普勒畸变信号,瞬时频率与原信号频率有着密切的关系。仿真信号和实验信号处理结果显示,多普勒效应带来的频带扩展问题得到了较好的解决,畸变信号得到了有效校正。     

基于采样值数字特征的压缩感知信号检测方法

由于压缩感知的采样值能够较好的保持原始信号的结构和信息,因此可以不重构原始信号,直接处理采样值完成原始信号的检测任务.目前的检测方法主要是基于信号的部分重构完成检测,这种方法在信噪比较低时,检测效果不好.针对这种情况,本文提出一种基于采样值数字特征的信号检测方法,根据采样值在不同假设下数学期望不同的特点,将实际采样值与其在各假设下数学期望的偏差作为判决依据,完成检测.实验结果表明,与传统方法相比,在低信噪比条件下,本文方法可以使用较少的采样点获得较高的检测成功率.     

Vienna 整流器网压重构功率控制

在电网电压不平衡下采用双闭环 PI 控制策略需对电网电压正负序分量分别控制,同时其参数整定较为复杂、稳定性能 较差。 为了简化在不平衡下的控制结构,提高系统的整体控制效果,提出了一种在电网不平衡下的 Vienna 整流器网压重构功 率控制策略。 首先,通过在 αβ 两相静止坐标系下对电网不平衡电压采用网压重构控制进行处理,减少了坐标变换,取消了正 负序分量分离;然后,从优化整定参数复杂性的角度,建立以瞬时功率理论为基础的预测功率数学模型,取消了 PI 控制器参数 的整定;最后,通过在 MATLAB/ Simulink 中搭建基于网压重构的预测功率控制与 PI 双闭环控制策略的仿真模型进行对比分析。 对比分析表明,相比于传统 PI 控制策略,控制策略在电网不平衡下降低了网侧电流总畸变率约 70% ,在电网不平衡且负载突变 下降低了约 40% ,并进一步在实验平台上验证了该控制策略的可行性。     

基于正交匹配追踪的压缩感知信号检测算法

在不重构信号的情况下,利用检测算法直接处理压缩感知信号获得的采样值可以完成信号检测任务。目前的检测算法中,作为判决依据的特征量仅由一次迭代过程决定。在感兴趣信号存在时,算法获得的特征量波动较大,影响检测性能。基于这种原因,本文提出一种改进算法,在每次迭代中基于正交匹配追踪思想修正特征量,降低特征量的波动,提高检测性能。实验结果表明,与原算法相比,本文算法获得的特征量波动小,相同检测阈值下,检测成功率高,相同检测成功率要求下,需要的采样点数少,允许的信噪比低。     

电网波形随机波动引起的测量误差的补偿

叙述电网电量测量原理，及电网波形随机波动引起的信号采样误差，提出了采样周期的跟踪技术以及在此基础上对采样数据加权处理的有样误差补偿方法。     

基于自适应脉宽的超声信号FRI采样方法及应用

脉冲超声信号求取包络后可视为具有有限新息率(FRI)的高斯脉冲串信号,对于FRI采样框架下的高斯脉冲串信号,时延和幅值的准确估计是以高斯脉冲宽度准确先验为前提的。针对此问题,研究了FRI采样框架下信号脉宽、时延和幅值的关系,并提出一种基于信号峰值先验信息的FRI采样方法,该方法可自适应调整脉冲宽度参数,无需准确先验脉宽参数,解决了传统FRI采样中脉宽准确先验的难题。通过仿真试验和在管道缺陷检测中的应用表明,即使在无法预知信号脉宽真实值的情况下,仍能准确从稀疏采样数据中估计得到信号的准确参数。     

适用于三相四线制的并联有源电网调节器的畸变电流观测方法

三简略介绍适用于三相四线制电路的并联型有源电网调节器系统结构与工作原理基础上,讨论了基于瞬时功率理论的负载畸变电流观测方法与负载零序功率的补偿。给出了两种分别适用于电源电压无高次谐波与含高次谐波的三相不平衡系统和畸变电流观测方法,并通过仿真对提出方法的有效性进行了验证。     

弱电网条件下的单相频率自适应锁相环

为消除直流偏置和谐波畸变对基于二阶广义积分器( SOGI )的单相频率自适应滤波器锁相环跟踪精度的影响,提出了一种级联结构的弱电网条件下的单相频率自适应锁相方法.分析了输入直流偏置对SOGI２ 路正交输出信号的影响,以及 SOGI 锁相环的频率跟踪特性.设计级联结构的双二阶广义积分器( DSOGI )锁相环,前级 DSOGI 消除单相电网电压采样信号中的直流偏置,生成 ２ 路正交电压信号,后级DSOGI 分离出 ２ 路正交信号中的基波正序分量,并抑制电网谐波畸变对锁相环相角与频率检测精度的影响.功率硬件在环实验装置上的实物实验验证了所提锁相方法的有效性.     

基于交比不变性的镜头畸变参数标定方法

在分析目前的畸变参数标定方法优缺点的基础上，提出了一种能克服现有技术缺点的简单快速的镜头畸变参数标定方法。该方法利用了透视投影中的交比不变性质，在畸变模型为一阶径向畸变的情况下，只需要空间共线的4个点的图像坐标和其交比，建立一元二次方程即可标定畸变参数。该方法的特点是算法简单，易于实施，需要已知条件少。对此标定方法进行了数字仿真实验和真实图像校正实验，证明该方法标定精度高，简单易行。     

Design and implementation of a high accuracy sampling wattmeter under non-sinusoidal and off-nominal frequency conditions

Errors may creep in when measuring active power under non-sinusoidal and off-nominal frequency conditions by a conventional regularly spaced sampling digital wattmeter (RSSDW) due to the existence of higher order voltage and current harmonics, and asynchrony between the signal fundamental frequency and the sampling rate. This paper presents design and implementation of a modified regularly spaced sampling digital wattmeter, called M-RSSDW, immune to above mentioned drawbacks of the conventional RSSDW. The proposed method utilizes a modified/ first degree digital integrator design technique, suitable for the distorted power system signals. The harmful truncation errors of asynchronous sampling have been reduced using numerical compensation method. Compared with the well-established technique such as Liangs’ method, the proposed algorithm provides higher degree of immunity and insensitivity to harmonics and frequency deviation. Structural simplicity, wide range of application and reduced computational load are other salient features of the proposed method. Based on simulation studies, the performance and validity of the proposed algorithm at different operating conditions have been presented and its accuracy and response time have been compared with the Liangs’ approach.     

Pure harmonics extracting from time-varying power signal based on improved empirical mode decomposition

Harmonic decomposition makes a great impact on power system operation, especially devices with frequency converters are widely used in modern society. In this paper, a hybrid method based on improved empirical mode decomposition enhanced with masking signals is presented to extract single-frequency harmonics from disturbed power signals accurately. The parameters for building masking signals are optimized by cooperative chaotic particle swarm optimization, where the Logistic chaos and cooperative evolution are employed to improve the convergence accuracy and avoid trapping into local minima. For improving the performance further, the improved fast Fourier transform based on Nuttall window and harmonics pre-extracting procedure are introduced to enhance the decomposition accuracy and reduce the instantaneous magnitude error in extracting time-varying power signal. The synthetic and field experiments demonstrate that the proposed method reveals significant improvements in the integrality and decomposition accuracy of harmonics extracted from time-varying power signal.     

基于瞬时无功功率理论的无功信号检测

分析了瞬时无功功率理论的ip—iq无功信号检测方法的原理,通过Matlab建立三相瞬时无功信号检测的仿真电路并进行仿真。以TMS320F2812 DSP芯片作为控制器件,采用硬件与软件相结合的方法实现了无功信号的检测,验证了该方法的有效性。     

考虑变幂数的畸变动力学相似试验模型设计方法及试验研究

动力学相似理论广泛应用于大型结构的振动试验，其中畸变相似用于解决结构的设计参数不满足等比例缩放时的相似问题，针对畸变相似关系中幂数为定值导致预测精度低的问题，提出考虑变幂数的畸变动力学相似试验模型设计方法。首先，在敏感性分析与中心差分理论推导的幂数表达式的基础上，将中心差分的范围不断扩大得到一组随相似比变化的幂数。采用最小二乘法将这组幂数拟合为关于相似比的函数并建立相似关系。然后，在多盘转子系统的数值算例中将变幂数法与文献中的两种方法进行对比，结果表明，变幂数法的预测精度较文献中的方法有很大提高。最后，通过试验研究验证了数值算例中动力学模型及临界转速求解的正确有效性。相似关系的建立是以模型的临界转速为基础，因此也验证了数值算例中的相似预测结果。     

A simple and precise real-time four point single sinusoid signals instantaneous frequency estimation method for portable DSP based instrumentation

A simple and precise instantaneous frequency estimation method of single sinusoid signals, using four equal spaced samples, for portable DSP based instrumentation is proposed. An analytical formula is obtained. Four-point instantaneous frequency estimator is sensitive to deviation of the sampling rate and quantization noise. As a demonstration of its simplicity, by implementing the proposed algorithm, a DSP based instantaneous frequency meter was built and tested with satisfactory performance.     

基于LMD和阶次跟踪分析的滚动轴承故障诊断

变转速工况下的滚动轴承故障振动信号具有多分量调制以及故障特征频率受到转频调制的特点,从而导致故障特征提取困难。对此,将局部均值分解(local mean decomposition,简称LMD)与阶次跟踪分析相结合,提出了一种变转速工况下的滚动轴承故障诊断方法。首先,采用阶次跟踪采样将时域滚动轴承故障振动信号转换到角域;然后,对角域信号进行LMD分解得到若干个乘积函数(product function,简称PF)分量;最后,对各个PF分量的瞬时幅值进行频谱分析,判断滚动轴承的故障部位和类型。通过对滚动轴承实验故障振动信号的分析,结果表明该方法能有效地应用于变转速工况下的滚动轴承故障诊断。     

A spectral estimation method for nonstationary signals analysis with application to power systems

In this paper we analyze a new method for estimating the spectral content of frequency and amplitude modulated waveforms in the context of power line signals where, as well known, the frequency of the fundamental component (50 Hz or 60 Hz) slightly changes over time. The method, proposed here in two distinct implementations, is based on a different choice of the harmonic functions that are usually used in the DFT as a basis to analyze signals. Indeed their frequency is allowed to change over time, according to the output of an instantaneous frequency detector. The orthogonality of the basis is preserved by performing a change of reference in the time. The theory is developed in continuous time and subsequently implemented in discrete time. Simulations and experimental results are provided in order to verify and characterize preliminarily the proposed method.     

Research on iterated Hilbert transform and its application in mechanical fault diagnosis

Multicomponent AM–FM demodulation is an available method for machinery fault vibration signal analysis, so a new method for mechanical fault diagnosis based on iterated Hilbert transform (IHT) is proposed. The principle of computing the asymptotically exact multicomponent sinusoidal model for an arbitrary signal by iterating Hilbert transform is introduced, and some properties of IHT are analyzed. Theoretical analysis for the generic two-component signal shows that there are limitations in the direct estimation of instantaneous frequencies via the phase signals of the previously obtained model. Therefore, a smoothed instantaneous frequency estimation (SIFE) method based on difference operator and zero-phase digital low-pass filtering is proposed, and then the accuracy and validity of this method have been proved by the simulation results. The analysis results of the mechanical fault signals show that the weak features of these signals can be efficiently extracted with the proposed approach.     

Doppler Effect removal based on instantaneous frequency estimation and time domain re-sampling for wayside acoustic defective bearing detector system

The phenomenon of Doppler Effect in the acoustic signal recorded by the wayside acoustic defective bearing detector (ADBD) leads to the difficulty for fault diagnosis of train bearings with a high moving speed, which is a barrier that would badly reduce the effectiveness of online defect detection. In order to improve the performance of condition monitoring of the bearings on a passing train with microphones amounted besides the railway, the elimination of the Doppler Effect should be solved firstly. An effective method for removing the Doppler Effect embedded in the source signal is presented in this paper. The Short Time Fourier Transform-Viterbi Algorithm (STFT-VA) is applied to obtain instantaneous frequency estimation of the distorted signal. According to the acoustic theory of Morse, the non-linear data fitting is then carried out to get the fitting instantaneous frequencies. The necessary parameters for time domain interpolation re-sampling, which is totally based on the kinematic analysis, are acquired from the fitting curve and the re-sampling sequence could be established in the time domain. As a result of the preceding steps, the fault diagnosis for the train bearings could be implemented with the restored signal. The effectiveness of this proposed method is verified by means of a simulation with three adjacent frequencies and an experiment with practical acoustic signals of train bearings with a crack on the outer race and the inner race. The results of the simulation and the experiment indicate that the proposed method has an excellent performance in removing Doppler Effect, and could be well employed to the condition monitoring and fault diagnosis of train bearings with a high moving speed.     

基于参数自适应时频分布的瞬时频率估计

为了跟踪信号在不同时刻的频率变化情况，需要估计其瞬时频率。本文分析了瞬时频率与非平稳信号的时频分布之间的关系，提出了一种采用自适应信号子空间分解的参数自适应时频分布（PAD），以及基于PAD峰值检测的瞬时频率估计方法。数值仿真和对实测信号的瞬时频率估计实验结果表明，该方法对于调频类信号的估计性能优于其他常用的瞬时频率估计法，且抗噪声干扰能力强，为时变频率非平稳信号的瞬时频率估计提供了新的手段。