【作者】 江亚群；

【导师】 何怡刚；

【作者基本信息】 湖南大学 ， 电工理论与新技术， 2009， 博士

【摘要】 随着国民经济和现代科学技术的飞速发展,电能质量问题正受到越来越多的关注。全面有效的检测和分析是改善和提高电能质量的前提和依据,快速、先进、有效的参数估计算法是实现有效检测和分析的基础。由于电力信号的复杂性和电能质量内涵的扩展性,以及不断提高的测量精度、广度与测量速度的要求,电能质量指标参数测量技术有待进一步发展和提高。本文依据国内外相关电能质量标准,结合电能质量研究现状和工程实际需要,应用数字信号处理技术及电力系统自动化技术,研究电能质量中最重要和最受关注的指标参数的测量理论和估计算法。主要工作包括:1)提出了一种基于自适应短时傅里叶变换的基波参数估计算法,并以此算法为基础计算电压偏差、频率偏差、三相不平衡度和功率因数等基本电能质量参数。算法采用固定的采样周期,采样频率不需随信号频率的变化而调整,实现简单;算法不需要迭代运算,可一次得到参数估计值,计算量小,响应时间快;通过采用矩形自卷积窗,并自适应地确定与信号频率相适应的时间窗宽度,有效抑制了频谱泄漏对基波参数测量的影响,测量精度高。2)根据谐波和间谐波各自的频谱特征,提出了一种新的谐波、间谐波实时检测算法。算法根据正余弦函数的特性,将各次谐波分量变换成直流分量,经由低通滤波后估计其有效值和初相角;从原信号中去除基波和谐波分量,再通过搜寻频谱极大值获取间谐波频率及有效值和初相角。算法实现简单,精度高,动态跟踪特性好,适合于离散频谱电压、电流信号的谐波、间谐波参数实时估计。3)谐波、间谐波和闪变关系密切,但现有谐波、间谐波的检测与闪变的检测实现方法不同且无关联。本文推导了间谐波和调幅波对于闪变的等价关系,在此基础上,将间谐波检测和闪变检测结合起来,根据国家标准和IEC标准的闪变检测技术规范,提出了一种基于间谐波估计的闪变参数检测新算法。新算法除了能求取瞬时视感度、短时间闪变值和长时间闪变值等反映闪变强弱的参数外,还能提供电压波动频度和幅度的信息,有利于电压波动与闪变的分析和治理,为闪变检测提供了一种新的实现模式。4)应用数字图像处理理论,采用图像边缘形态检测算子,实现了暂态电能质量扰动的检测和时间定位。该方法具有实现简单,计算量小,对采样频率要求低,实时性好等特点,可对电压暂降、暂升、短时中断、短时高频振荡、陷波等常见暂态电力扰动进行有效检测。5)减小背景梯度是实现暂态电能质量扰动检测的关键。针对非扰动情况下电力信号周期交替变化引起的背景梯度,提出了基于Top-Hat形态变换的抑制方法,针对噪声引起的背景梯度,构造了合适的形态滤波器,提高了扰动检测的灵敏度。6)提出了基于顺序形态学和Top-Hat形态变换的扰动检测方法,既可有效抑制信号平稳变化引起的背景梯度,又具有较好的抗噪声能力,同时很好地保留了扰动信号突变的局部细节,保证了扰动检测灵敏度和时间定位精度。7)提出了一种改进的单相电压暂降特征参数实时检测算法。通过构造新的变换矩阵,减小了传统方法构造虚拟三相系统的延时,可对单相电压暂降幅值、持续时间和相位跳变等特征参数进行近乎瞬时的估计。分析了单相电压暂降检测时“异动”现象的产生原因,提出了基于形态运算的解决方法。8)提出了一种改进的三相电压暂降检测算法。针对三相不平衡电压暂降,通过正序dq变换和负序dq变换,经由形态低通滤波得到三相电压的基波正序、负序分量,采用改进的单相电压暂降检测算法得到零序分量,进而得到各相电压暂降的特征参数。改进方法实时性好,参数估计精确,满足电压暂降实时检测的要求,可应用于电压暂降监测、评估及动态电压恢复器(DVR)对电压暂降的实时补偿控制。本文提出的电能质量参数估计理论和系列算法,为电能质量实时检测和离线分析提供了有效的工具。仿真研究验证了所提算法的可行性和有效性;算法已成功应用于“基于虚拟仪器技术的电能质量综合测试仪”的研制和开发中。更多还原

【Abstract】 With rapid development of economy and science technology, power quality (PQ) problems have increasingly become a substantial concern in recent years. Completely and accurately assessing power quality is the first step in solving and mitigating the problems, fast and advanced algorithms are the basis for effective measurement and evaluation.Due to the complexity of power system signal and the variety of power quality event, it is a challenge to detect power quality indices completely, accurately and promptly.In accordance with national and international power quality standard, a systematic and in-depth research about power quality major indices evaluation is carried out based on analyzing domestic and overseas research situations. By use of digital signal-processing methods as well as power system automation techniques, the research works pay more attention to the measurement theories and estimation algorithms of important indices. The main contributions of this dissertation are listed as follows:1)A new digital algorithm based on adaptive Short-Time Fourier Transform (STFT) is presented to estimate some basic power quality indices, such as voltage deviation, frequency deviation, voltage unbalance degree and power factor of fundamental component. The algorithm employs fixed sampling period although the frequency of the signal varies. No recursive calculation is needed to get evaluation values of above mentioned parameters. As a result, the algorithm is easy to implement with less computation burden and short response time. To restrain the spectrum leakage of harmonics, a novel kind of window called Rectangle Self-Convolution Window (RSCW) is adopted and the window length is adjusted according to the frequency variation of the signal. It is thus suitable for real-time measuring with high presicion.2)According to the spectrum characteristics of harmonics/inter-harmonics, an approach is proposed to compute harmonics/inter-harmonics in real time. Considering the characteristic of sine/cosine function, the harmonic component can be transformed into DC component, the rms value and initial phase angle of harmonic then can be got after low-pass filtering. As to inter-harmonics, it is generally considered to be a challenge because the inter-harmonics only have small ratio, it is hard to estimate them accurately. By subtracting fundamental and harmonic components from the original signal, maximum spectrum searching technique is used to compute frequency, rms value and initial phase angle of inter-harmonic. The proposed approach is easy to implement with high precision and good dynamic tracking feature, it suits to estimate harmonic/inter-harmonic parameters of voltage or current signals with discrete spectrum.3)It is known that flicker phenomena are closely related with harmonics and inter-harmonics, but at present, the detection methods of harmonics/inter-harmonics and flicker are completely different. Based on deducing the equivalent relation of inter-harmonic and amplitude modulation wave to flicker, the detection methods of inter-harmonic and flicker are combined. Therefore, according to national and International Electrotechnical Commission (IEC) standard, a new flicker evaluation algorithm is presented based on inter-harmonic estimation. The algorithm can not only compute instantaneous visual acuity, short-term flicker severity index and long-term flicker severity index, but also provide frequency and amplitude imformation of voltage fluctuation, thus, it benefits to analyze and manage voltage fluctuation and flicker. Furthermore, it provides a novel implemental model for flicker detection.4)To detect and locate non-steady-state disturbances, digital image processing theory and image edge morphology detecting method are introduced. The outstanding features of the method are easy implementation, less computing complexity, high time resolution and low demand of sampling frequency, therefore, it can be used to effectively detect common power disturbances such as voltage sag, swell, short-time interruption, short-time high frequency oscillatory, notching , etc.5)Deep analysis reveals that restrain background gradient is the key step for disturbing detection. Based on examining the origin of background gradient, two different methods for restrain background gradient are proposed. One uses Top-Hat morphology transform to restrain the background gradient produced by normal periodic alternation of analyzed signal, the other constructs suitable morphology filters to restrain the background gradient introduced by noises. Thus, the detecting sensitivity can be improved obviously.6)A new disturbing detection method based on order morphology and Top-Hat transform is then presented. It can not only restrain the background gradient produced by steady variation of analyzed signal, but also resist noises while keep the partial details of signal’s abrupt change. Therefore, it ensures the sensitivity and time locating precision of distrurbing detection.7)An improved single phase voltage sag dececting algorithm is put forward. A new matrix, which is designed to decrease the phase delay that is unavoidable in traditional fictitious three phase systems, is constructed. The improved algorithm can almost instantaneously quantify the magnitude, duration and angel jump for voltage sag in single phase systems. Since‘abnormal variation’phenomenon presents in the detecting process, a corresponding solving measure is carried out based on morphology calculation.8)As to three phase unbalanced voltage sag, an improved detection method is also presented. After carrying out positive and negative dq transform, morphology low pass filter which possesses the superiority of high accuracy and fast dynamic performance compared with traditional Butterworth filter is used to obtain positive-sequence fundamental component and negative-sequence fundamental component, and the zero-sequence component is obtained by using improved single phase voltage sag detection method, then, voltage sag characteristics can be got easily. The improved method can estimate the sag parameters with high accuracy in real time. Therefore, it is not only efficient for the real-time detection of voltage sag but also effective for the real-time voltage sag control and compensation in dynamic voltage restorers(DVRs).The purpose of the dissertation is to form an arithmetic system that related to some main power quality problems. It will provide effective theorem basis and algorithms for power quality on-line detection and off-line analysis. The validity of the proposed algorithms has verified by normorous simulations, and the algorithms have been successfully applied in the development of a practical device named‘the VI-based Electric Parameter Measurement Device’.更多还原