基于改进递归DFT与SVR融合的实时谐波检测

根据电力系统中以整数次谐波检测为主要目标的情况,通过对递归离散傅里叶变换(DFT)和快速傅里叶变换(FFT)算法的分析比较,提出了改进递归DFT算法,即在递归DFT运算之前对首次采样做FFT运算,再将此运算结果作为递归DFT运算的初始值以进一步减少运算量.为同时提高检测精度,提出了基于改进递归DFT与改进序列最小最优化(SMO)的支持向量回归(SVR)融合的整数次谐波检测新方法.通过算例仿真,并与递归DFT及改进递归DFT相比较,证明了改进递归DFT与改进SMO的SVR融合的方法检测精度高,非常适合整数次谐波的实时检测和分析.     

基于递推离散傅里叶变换和同步采样的谐波电流实时检测方法

目前普遍采用的谐波检测方法存在工频周期延时、计算量大等不足,文章提出了一种基于离散傅里叶变换的快速谐波检测方法。该方法采用递推方式动态更新频谱,并根据相位计算结果实时跟踪电网频率变化,动态调整采样频率,实现同步采样,有效抑制了电网频率波动对检测精度的影响。4种不同情况的仿真实验结果表明,该方法实现简单、计算量小,能实时检测出基波与指定次谐波的参考指令电流。     

一种测量电信号基波分量的快速算法

针对传统的ＤＦＴ和ＦＦＴ算法的缺陷,讨论改进的受谐波干扰的电信号基波分量快速算法。此算法较大地提高了计算效率,可用于实时控制、无功功率和谐波补偿以及功率和能量实时计算等领域。     

基于同步旋转变换及DFT的SVG指令电流检测法

为使静止无功发生器(Static Var Generator,SVG)具备无功、谐波及不对称电流综合补偿能力,提出了一种基于同步旋转坐标变换及离散傅立叶变换(Discrete Fourier Transform,DFT)的SVG指令电流检测方法。该方法通过在同步旋转坐标系下进行递归离散傅立叶变换,能够实时检测出负载电流中的无功分量、不对称分量以及特征谐波。利用该方法只用一个控制器就能同时对两种特征谐波分量进行补偿,相对于其他方法运算量大大减小,便于工程实现。仿真和实验验证证明了该方法的有效性。     

Real-time electrical variables estimation based on recursive wavelet transform

In frequency and phasor estimation algorithms, the undesired components are required to be filtered out from the original signals. In power systems, the undesired components are the decaying dc offset and harmonics. These components could cause delay in algorithm convergence time and deviation from the desired results to a great extent. This paper proposes a new recursive algorithm for accurate and fast estimation of the instantaneous electrical variables such as frequency, amplitude and phase angle. The new algorithm provides an improvement over the existing recursive wavelet transform and, therefore, it is called IRWT. The IRWT performance is compared with the commonly used full-cycle discrete Fourier transform (DFT) and the recursive wavelet transform (RWT) methods. Since it uses a special mother wavelet function, it reduces computational complexity compared to the conventional DFT based method. Compared to the recursive wavelet transform (RWT) method, it has a faster response time. It is shown that IRWT possesses an improvement over a wide range of decaying dc component, harmonic distortions, frequency deviation and sampling frequency compared to the previously proposed methods. This characteristic of IRWT makes it a good candidate for the real-time applications in any power systems.     

A practical method to improve phasor and power measurement accuracy of DFT algorithm

Centralized control, which can overcome the ill interactional effects among decentralized controllers, impels a real need for fast and reliable computational algorithms to improve the accuracy of phasor and power measurements. This paper deals with discrete Fourier transform (DFT)-based measurement techniques. Based on the practical frequency tracking method proposed by the same authors in another paper, this paper develops practical compensation method to improve the phasor and power measurement accuracy of the DFT algorithm. The method proposed by this paper takes full advantage of the DFT algorithm. It simply modifies the DFT results. With notable accuracy improvement, the calculation burden of the proposed method is little more than the DFT algorithm. The method can be used for on-line purposes. Though the analog signal studied in this paper is sinusoidal signal, the method proposed by this paper has good performance in the presence of harmonics. Some examples are given to demonstrate the feasibility, simpleness and robustness of the proposed method.     

A precise calculation of power system frequency

A precise digital algorithm based on discrete Fourier transforms (DFT) to estimate the frequency of a sinusoid with harmonics in real-time is proposed. This algorithm, that the authors call smart discrete Fourier transforms (SDFT), smartly avoids the errors that arise when frequency deviates from the nominal frequency, and keeps all the advantages of the DFT e.g., immunity to harmonics and the recursive computing can be used in SDFT. These make the SDFT more accurate than conventional DFT based techniques. In addition, this method is recursive and very easy to implement, so it is very suitable for use in real-time. The authors provide the simulation results compared with a conventional DFT method and second-order Prony method to validate the claimed benefits of SDFT     

基于递推积分PI的混合型有源电力滤波器电流控制

在采用混合型有源电力滤波器消除谐波时，由于滤波器的检测精度、指令电流计算延时和输出滤波器的相移等因数的影响，滤波效果不够理想，针对被控量是以20ms为周期的电流，文中提出了应用于混合型有源滤波器的递推积分PI控制算法，并且引入了参考电流模糊加权前馈控制。该控制方法有效地提高系统的目标跟随特性、抗干扰性和鲁棒性，并且具有计算量小、容易工程实现的特点，实验结果证明了所提出的控制方法的可行性。所提出的递推积分H控制算法还可以对周期性的被控量实现无静差控制，如交流电机的闭环控制。     

一种适用于微机保护的新的递推DFT算法

为减少离散傅里叶变换(DFT)算法的计算量,人们利用一种很自然的增减数据项的方法提出了递推傅里叶变换算法,但在某些情况下,该传统递推算法并不太适用。文中基于三角函数的和差公式以及线性方程组的求解,提出了一种新的递推离散傅里叶变换算法,它的计算量与传统递推算法接近,但可以解决传统递推算法不易解决的许多问题,如适用于人们提出的克服电力系统中衰减直流分量对DFT影响的一些方法中,因而具有广阔的应用前景     

一种新型混合型大功率有源电力滤波器电流控制方法

在采用混合型大功率有源电力滤波器消除谐波时,由于滤波器的检测精度、指令电流计算延时和输出滤波器的相移等因数的影响,滤波效果不够理想,针对这一问题,笔者提出了应用于混合型大功率有源滤波器的模糊递推积分PI控制算法。该方法能有效地提高系统的目标跟随特性、抗干扰性和鲁棒性,并且具有计算量小、工程容易实现的特点。实验结果证明了所提出的控制方法的可行性。所提出的模糊递推积分PI控制算法还可以对周期性的被控量实现无静差控制,如交流电机的闭环控制。     

含分数次谐波环境下提取整数次谐波信息的新方法

提出了一种在含有分数次谐波环境下,以一定的规律逐渐降低的频率序列依次作为基频,利用傅里叶级数展开电力系统中实际的电压、电流信号,再通过迭代算法从中提取出工频量及其整数次谐波分量信息的新方法。该方法回避了现有的加窗DFT算法中选取窗函数困难的问题。新方法的原理进行了详细的数学推导和说明,并给出程序框图。为了验证方法的正确性,利用程序对一实际信号进行了分析。实例结果表明,与传统的FFT算法比较,新方法在富含间谐波和次谐波环境下依然能够提出基波和整数次谐波的幅值和相角,且精度满足工程需求。同时,该方法还具有实现简单等优点,易于在工程实际中应用。     

基于高精度测频的修正DFT相量及功率测量算法

为了提高频率偏移时电力系统相量及功率测量精度,提出了一种基于改进扩展卡尔曼滤波(IEKF)频率测量的修正离散傅里叶变换(DFT)相量及功率测量算法。分析了频率发生偏移时非同步采样下DFT的测量误差,建立了相角、幅值与频率偏移量和初相角之间的函数关系式。由IEKF得到频率偏移量,然后对DFT计算结果进行修正即可得到输入信号的真实相量和功率。仿真结果表明:该算法相比较于传统自适应DFT算法能有效消除或减弱谐波、噪声以及频率偏移对相量同步测量的影响,提高了相量及功率测量精度。     

Covariance management based RLS algorithm for phasor estimation inseverely noisy systems

This paper presents a new algorithm, derived from the recursive least squares (RLS), to estimate power system voltage and current harmonics for digital relay purposes. The algorithm is based on the RLS covariance matrix management, by making use of the covariance resetting in a different way. The approach provides a kind of attractor that absorbs all nonmodeled dynamics. In order to demonstrate its effectiveness, the proposed algorithm is applied to simulated signals and its performance is compared with other conventional methods     

基于DFT的电力系统相量及功率测量新算法

随着全球定位系统(GPS)的全面民用化以及通信技术的发展，电力系统实时相量测量技术日益受到关注。传统的基于离散傅里叶变换(DFT)的频率跟踪算法对相角误差的考虑不全面，从而其频率、相角、幅值等计算结果也不够准确。文中对 DFT 在非同步采样情况下的误差产生机理进行了全面分析，给出了非同步采样情况下 DFT 相角计算结果的精确误差表达式，基于该相角误差公式，提出了一种新的基于 DFT 的电力系统相量测量算法。与传统算法相比，该算法具有精确度高、可以自适应地抑制谐波干扰、计算量不大等优点，并用算例验证了这些优点。此外，还给出了实用的利用传统 DFT 方法计算功率的误差估计公式。     

具有快速动态响应的数字功率因数校正算法

为了提高功率因数校正(power factor correction,PFC)输出电压对负载变化的动态性能,在分析电压环对输入输出谐波影响的基础上,提出一种快速动态响应数字PFC算法。该算法通过增大电压环带宽来提高负载动态响应速度,采用矢量旋转方式产生谐波补偿量来抵消因电压环带宽增大引起的二次谐波。它无需增加外围硬件电路,通过与控制芯片相对应的图形化编程方式完成快速动态响应数字算法。实验结果表明当负载功率发生大范围变化时,所设计的系统具有快速动态响应能力,同时输入电流总谐波畸变率(total harmonic distortion,THD)小于10%,功率因数达到0.99。     

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     

一种实用的幅值和功率测量新算法

为解决电力系统全局信息的快速准确测量问题,提出了一种实用的幅值和功率测量算法。结合电力系统实际情况,对离散傅里叶变换(DFT)算法中的强非线性部分进行了合理简化,从而可以方便地利用DFT计算结果对其自身进行补偿修正。该算法充分利用了DFT算法的快速、对谐波有抑制能力的优点。与传统DFT方法相比,文中方法测量精度有明显提高,且计算负担增加很少。算例验证了这一特点。     

用于谐波和间谐波检测的频谱分解法

在使用离散傅里叶变换进行电力系统谐波/间谐波分析时,若所分析信号中两频率成分过于密集,就会产生主瓣干扰。本文分析了传统方法在两频率成分发生主瓣干扰时失效的原因,在10个周波采样长度下,提出一种用于抑制主瓣干扰的改进傅里叶算法:根据频域谱线的相位特性,将两个密集频率成分的傅里叶变换结果拆分成两组谱线,分别对这个两组谱线进行频率、幅值以及相位的校正。计算机仿真算例和实测分析表明,该方法计算简单,能在抑制旁瓣干扰的同时,有效拆分出信号中频率差小于频率分辨率的谐波与间谐波成分,或两个间谐波成分,满足工程精度要求。     

Removal of decaying DC in current and voltage signals using amodified Fourier filter algorithm

Protecting transmission lines frequently involves applying distance relays. Protective relays must filter their inputs to reject unwanted quantities and retain signal quantities of relevant interest. Accuracy and convergent speed of filter algorithm are essential for protective relays. A widely applied filter algorithm, the discrete Fourier transform (DFT) can easily remove integer harmonics using simple calculation. However, the voltage and current signals contain serious harmonics and decaying DC during the fault interval. In addition, the decaying DC and higher order harmonics seriously decrease the precision and convergence speed of fundamental frequency signal from DFT. In this investigation, the authors derive a novel algorithm which combines the appropriate analog low pass filter and modified full cycle DFT (FCDFT) or half cycle DFT (HCDFT) algorithm to remove the decaying dc in a voltage or current signal. Using the Electromagnetic Transients Program (EMTP) simulates the transient responses of transmission lines during the fault period. Applying the proposed algorithm in distance relays effectively suppresses the decaying DC and quickly decomposes the accurate fundamental frequency components     

Slow sampling on-line harmonics/interharmonics estimation technique for smart meters

This paper presents a modified gradient search (MGS) technique to estimate harmonics/interharmonics of power system voltages and currents. The proposed technique, which is applied to spectral estimation, consumes very low processing power and needs a few samples per cycle for real-time implementation in smart meters. The computational burden of the proposed technique is lower than the discrete Fourier transform (DFT) and fast Fourier transform (FFT) and can be implemented recursively on digital signal processors (DSPs). In addition, the effects of slow sampling on the accuracy and estimation latency have been investigated. Performance of the proposed method is evaluated by simulations in MATLAB-Simulink and confirmed by experimental results.