Power components estimation using two-stage Newton type algorithm

In this paper an efficient two-stage Newton type algorithm for power components estimation is presented. In the first algorithm stage the spectra and fundamental frequency of input currents and voltages are estimated. In the second stage the power components are calculated based on the results obtained in the first stage. By this, power components definitions according to the IEEE Standard 1459-2000 are used. In the algorithm the signal frequency was considered as an unknown parameter simultaneously estimated with signal spectrum. By this, the algorithm becomes insensitive to frequency changes. On the other hand, the signal model became non-linear, so the strategies of non-linear estimation were used. The algorithm performances are tested using computer simulated and laboratory tests.     

非正弦非平衡电力系统视在功率研究

电力系统中非线性元件的急剧增加,造成电流电压波形的畸变和不对称日益严重。尽管非正弦波形下有功功率的定义已确定无疑,但视在功率的定义存在争议,导致功率因数的差异。对工业界广泛使用的算术视在功率和矢量视在功率与IEEE1459-2000试行标准中有效视在功率的定义进行了对比分析,通过线损和视在功率的关系证明了传统定义的局限性和有效视在功率定义的科学性;以三相不对称的牵引电力网为例,根据德昌牵引变电所实测数据进行了仿真试验,通过计算结果的分析,证实了有效视在功率在实际应用中的现实意义。     

STLS Algorithm for Power-Quality Indices Estimation

This paper introduces a new two-stage, self-tuning least-squares digital signal processing algorithm for power-quality (PQ) indices estimation according to the power components and PQ indices definitions given in the IEEE Standard 1459-2000. The algorithm is based on the nonrecursive least error square technique accompanied with an tuning procedure, which generally improves the algorithm properties: the measurement range, the immunity to a random noise, convergence, and accuracy. The presented algorithm models typical signal distortions and it can be used for the real-time PQ indices estimation. In order to estimate signal spectra and fundamental frequency, current and voltage signals are processed in the first algorithm stage, whereas in the second stage, the power components and PQ indices are calculated based on the results obtained from the first stage. To demonstrate the efficiency of the proposed algorithm, the results of computer simulated and laboratory tests are presented.     

Performance evaluation of WPT based islanding detection for grid-connected PV systems

Recent developments in power electronics technology have emerged towards the generation of electrical power from the renewable energy sources. Among renewable energy sources, solar energy has garnered more importance because of less maintenance and environmental friendly. In grid connected mode, distributed power generation system (DPGS) requires reliable islanding detection technique to find the electrical grid status and operate the grid connected inverter effectively. This paper investigates a comparative performance analysis of wavelet transform (WT) and wavelet packet transform (WPT) based detection in a three-phase grid connected PV inverter system under various power quality disturbances and islanding situation. The WT and WPT coefficients are determined by applying db4 wavelet basis functions, which are obtained optimally for analyzing perturbations that occur in grid connected PV system. The wavelet transform produces large errors due to spectral leakages in frequency bands. On the other hand, WPT provides uniform frequency subband with better time frequency resolution over WT. Finally, the feasibility of proposed WPT based islanding detection method is verified by simulating the system in MATLAB/SIMULINK environment. The simulated results demonstrate the better performance of WPT over WT technique and proved as an accurate, fast and reliable detection technique.     

Accurate and Computationally Efficient Implementation of the IEEE 1459-2000 Standard in Three-Phase Three-Wire Power Systems

The definitions for the measurement of electrical power quantities under sinusoidal, nonsinusoidal, balanced, or unbalanced conditions are established in IEEE Standard 1459-2000. Measured magnitudes, such as apparent powers or effective quantities, are evaluated considering the frequency spectrum of voltage and current signals (fundamental, nonfundamental, and combined magnitudes). Previous papers implement these definitions in the frequency domain (DFT) and in the time domain (Clarke-Park Transformations). In the time domain, low-pass filters (LPFs) must be applied to obtain the fundamental magnitudes but, in this case, the quality of the measurements depends on the LPFs orders and their cutoff frequencies. This paper proposes a time-domain implementation of the standard definitions without LPFs and employs a recursive averaging algorithm which improves the measurements precision and reduces the computational burden. Simulation and experimental tests showing the proposed method performance are included     

Non-fundamental effective apparent power defined through an instantaneous power approach

This paper proposes a new definition of non-fundamental effective apparent power based on an analysis of instantaneous power flows. This new instantaneous power approach for the calculation of the non-fundamental effective apparent power extends, and adapts for new electrical conditions, the procedure applied by IEEE Std. 1459 for the quantification of active and reactive power in single-phase systems.This proposed approach is based on the analysis of per-phase and three-phase instantaneous power flows when a three-phase four-wire balanced non-linear load is connected to an ideal power network that supplies a set of positive-sequence fundamental voltages. The per-phase and three-phase instantaneous power flows caused by positive-, negative-, and zero-sequence harmonic load currents are analyzed. The results obtained for the load zero-sequence harmonic currents disagree with the results obtained when applying IEEE Std. 1459. As a consequence, a new definition of the effective quantities is proposed. A comparison between the new definitions and IEEE Std. 1459 definitions is made in the paper.     

一种基于小波包变换的电力系统谐波检测方法

非线性设备的大量使用和分布式电源的投入使得谐波污染愈加严重,文中提出了一种基于小波包变换的谐波检测方法,能对电能质量进行有效的分析。该方法在五层db40小波包变换的基础上,利用希尔伯特变换做移频运算,避免了中间频段小波混叠对检测精度造成的不利影响,并将各次谐波分量转移到精度较高的边频带进行小波包分解并重构信号,实现了各次谐波的高精度检测,同时通过Matlab工具对不同算法的仿真进行了比较和误差分析。仿真表明,相比于传统傅里叶变换,该算法具有高分辨率时频分析能力,能有效定位暂态干扰;与经典小波包变换相比,测量精度也有了较为明显的提高,实验结果一致显示了该算法的可行性和优越性。     

Novel power quality indices based on wavelet packet transform for non-stationary sinusoidal and non-sinusoidal disturbances

High power quality (PQ) level represents one of the main objectives towards smart grid. The currently used PQIs that are a measure of the PQ level are defined under the umbrella of the Fourier foundation that produces unrealistic results in case of non-stationary PQ disturbances. In order to accurately measure those indices, wavelet packet transform (WPT) is used in this paper to reformulate the recommended PQIs and hence benefiting from the WPT capabilities in accurately analyzing non-stationary waveforms and providing a uniform time–frequency sub-bands leading to reduced size of the data to be processed which is a necessity to facilitate the implementation of smart grid. Numerical examples’ results considering non-stationary waveforms prove the suitability of the WPT for PQIs measurement; also the results indicate that Daubechies 10 could be the best candidate wavelet basis function that could provide acceptable accuracy while requiring less number of wavelet coefficients and hence reducing the data size. Moreover, a new time–frequency overall and node crest factors are introduced in this paper. The new node crest factor is able to determine the node or the sub-band that is responsible for the largest impact which could not be achieved using traditional approaches.     

基于平稳小波包分解的水轮机非平稳振动信号希尔伯特谱分析

应用平稳小波包变换对信号进行窄带分解,避免了经验模式分解过程中虚假模式分量的产生以及高频本质模式函数瞬时频率的波动,改善了Hilbert谱对于高频宽带信号的频率分辨率,使其更加适合复杂多分量的非平稳信号分析。针对水轮机过渡过程中转子振动响应的复杂性和非平稳性,应用该方法对停机和起动过程现场测试信号进行分析,识别了信号的时频结构特征,主轴振动响应主要由转速频率及其谐频成分组成,其中主导成分为转速频率。与Hilbert-Huang变换的对比验证了该方法在分析水轮机过渡过程非平稳振动信号方面的有效性。     

利用小波包变换实现电力系统谐波分析

小波包变换(WPT)建立在小波变换的基础上,可以实现信号频带的均匀划分,能够更好地提取信号的时频特性,具有更好的谐波分析特性.但是现有的小波包变换算法实现的频带划分不是按频率大小顺序排列的,给系统和谐波分析带来混乱.根据采样定理和滤波器组实现电路分析了小波包变换实现频带划分的特点,并利用改进的小波包变换实现算法进行系统分析,实例验证这种新的小波包分解结构对谐波分析具有更好的特性.     

Adaptive Real-time Power Measurement Based on IEEE Standard 1459-2010

This article presents the theoretical development and implementation of an adaptive algorithm for real-time measurement of electrical powers under sinusoidal, non-sinusoidal, balanced, and unbalanced conditions according to the definitions given by IEEE Standard 1459-2010. The algorithm is based on adaptive filter notch filter implementation, where the parameters are adjusted by tracking the amplitude and phase variations to improve the accuracy of the power measurement. The algorithm uses the filter coefficients to calculate powers, resulting in low computational burden. The results of computer simulation and practical implementation using a fixed-point digital signal controller are shown in detail, proving the accuracy and efficiency of the algorithm.     

Two-Stage Improved Recursive Newton-Type Algorithm for Power-Quality Indices Estimation

In the paper, a new improved recursive Newton-type algorithm (IRNTA) suitable for various measurement applications in the electric power systems is presented. Here, it is applied for power-quality (PQ) indices estimation according to the IEEE Standard 1459-2000. Basically, the algorithm is a recursive nonlinear estimator, improved with a strategy of sequentially tuning the forgetting factor. This approach generally improves the algorithm performance: immunity to random noise, accuracy, and the speed of convergence. The IRNTA considers the power frequency as an unknown model parameter and takes into account distortion of voltages and currents. Therefore, it is suitable for the real-time PQ monitoring. The algorithm has two stages. In the first stage, the input signal spectra and fundamental frequency are estimated, whereas in the second stage, the unknown PQ indices are calculated. To demonstrate the efficiency of the proposed algorithm, the results of computer simulations and laboratory testing are presented.     

Global method for time–frequency analysis of harmonic distortion in power systems using the wavelet packet transform

The paper proposes a method based on the use of the wavelet packet transform for the time–frequency analysis of harmonic distortion in power systems. The magnitude of harmonic and interharmonic groups, as defined in Standard IEC 61000-4-7, the magnitude of the subharmonic group, defined as an extension of the standard method, and the time evolution of odd harmonics in voltage and current waveforms can be simultaneously computed using different levels of the same wavelet decomposition tree applied to the samples of the input signal. The paper shows the performance of the method proposed in different measurement conditions and the comparison of the results with those obtained applying the standard method.     

Improved fault location algorithm for radial distribution systems with discrete and continuous wavelet analysis

This paper presents a novel wavelet based approach for fault location using voltage transient waveforms in power distribution systems. The proposed method includes two main stages. Firstly, the approximate location of the fault or fault section is determined using a new algorithm with discrete wavelet transform. The difference between arriving times of transient components in different measurement units is used for this purpose. The accurate location of the fault is determined in the second stage. Depending on the determined fault section, the difference between arriving times of transient components in different measurement units or the frequency content of the voltage transients are used. The time difference and frequency content are calculated using discrete and continuous wavelet transform (DWT and CWT) respectively. The proposed technique is implemented on an unbalanced 34 bus distribution system with two distributed generation units which is simulated in ATP–EMTP. The comparison of the results of the proposed method with previous works verifies its better accuracy and more robustness to fault conditions including fault inception angle and fault resistance.     

电力信号短时扰动的检测及自动分类

针对电力短时扰动信号具有非平稳、突发性的特点,应用小波变换的多分辨率分析特性检测扰动信号的特征参量,依据IEEE制定的短时电能质量扰动标准,提出了一种逐次逼近型的快速分类法。利用小波变换对扰动信号的奇异点进行检测,发现通过对扰动信号奇异点的检测可以准确地定位短时扰动的起始时刻、持续时间和扰动幅度。提出的逐次逼近型分类法,用一组8位二进制数逼近扰动的持续时间和扰动幅度两个参数,不仅可以将短时扰动信号按照IEEE制定的标准进行准确分类,而且还可以大大减少分类过程中的计算量,充分满足了电力信号监测的实时性要求。     

A new IEEE Std 1459-2000—Compatible time-domain formulation for apparent power

This paper presents the development of new time-domain equations related to the definition of apparent power. These equations are compatible with the IEEE Std 1459-2000 Standard. When the application of these formulations involves an adequate quantity of samples, thus obeying the Nyquist Criterion, they can be utilized without restrictions regarding distortion, imbalance and asymmetry. Thus, they may be used in numeric meters for power measurements. In addition, unlike the above-mentioned standard, they do not oversimplify with respect to the phase and neutral resistance ratio or the percentage of delta-connected and wye-connected loads.     

Definitions of apparent power and power factor in a power system having transmission lines with unequal resistances

Recently, disputes in power theory seem to be settled and a new trial-use standard has been prepared as the IEEE Standard 1459-2000. However, since uniform line resistances are assumed, it is not enough not only for increasing transmission systems, such as parallel ac/dc systems, but for a three-phase four-wire system whose neutral line has a different thickness from the other lines. In this paper, a generalized power theory applicable to a system having transmission/distribution lines with unequal resistances is proposed, which is applicable to any kind of power system: from a single-phase system to a multiline system having transmission lines with equal or unequal resistances under asymmetric and/or nonsinusoidal conditions.     

Summary of IEEE standard 1459: definitions for the measurement of electric power quantities under sinusoidal, nonsinusoidal, balanced, or unbalanced conditions

This paper describes the new IEEE Standard 1459, Definitions for the Measurement of Electric Power Quantities Under Sinusoidal, Nonsinusoidal, Balanced or Unbalanced Conditions. The information is presented in the context of historical events that explain the reasons for new definitions. The new definitions originate from S/sub e/, the effective apparent power definition attributed to F. Buchholz and W. Goodhue. The resolution of S/sub e/ extends from well-established concepts. The need for the separation of 60/50-Hz powers from the non-60/50 Hz-powers is emphasized. The standard serves users who want to evaluate the performance of modern equipment or to design and build the new generation of instrumentation.     

Comparison of control strategies for DSTATCOM in three-phase,four-wire distribution system for power quality improvement under various source voltage and load conditions

This paper presents comparison of three different control strategies to generate reference current components for Distribution Static Compensator (DSTATCOM). Reference currents are tracked by a three-phase voltage source converter in a hysteresis band control scheme. These methods are instantaneous reactive power (IRP) theory, symmetrical component (SC) theory and an improved instantaneous active and reactive current component (IARCC) theory. The performance of three methods has been evaluated under various source voltage and load conditions with new IEEE Standard 1459 power definitions. A comparative study of their performance in terms of rms value of source current, Total Harmonic Distortion (THD), supply power factor and compensator ratings is also presented. A three-phase, four-wire distribution system supplying linear as well as non-linear load is considered for simulation study which is carried out using MATLAB/SIMULINK software. Under balanced and sinusoidal source voltage conditions, all three control strategies similar performance while an improved IARCC theory outperforms, particularly, under unbalanced and distorted source voltage conditions.     

一种基于离散小波变换的谐波分析方法

在离散小波变换的基础上,结合加窗插值FFT,提出了一种组合式谐波分析算法。该算法先用加窗插值FFT计算基波频率,然后对加窗信号进行频率调制,将谐波分量变换成直流或近似直流分量。用离散小波变换分离出这些分量后用于计算谐波幅值和相位。计算机仿真和实验结果表明,该算法可在高噪声污染情况下,准确计算谐波参数,尤其谐波相位角。DSP评估板上的实现证明了该算法可用于实时谐波分析。