摘要
随着电力电子器件在电网中的大量应用,电网谐波污染日益严重。谐波的测量和分析是实现谐波治理的前提条件,也是谐波的治理的依据。通过离散傅立叶变换(DFT)对电网谐波信号进行分析是常用的方法。但是,由于非同步采样以及时域、频域有限化和离散化等等原因,常规的DFT对信号进行频谱分析时会产生较大的误差,测量的结果往往难以满足检测的要求以及实际分析的需要。因此进一步探讨电网谐波信号的频谱泄漏问题,以及寻求相应解决的途径,具有重要的理论意义和实用价值。
本文首先对谐波信号频谱泄漏的根源进行了分析,讨论和给出了在非同步采样条件下截断信号与原始待分析信号之间的相位偏转关系。传统的频谱分析方法是通过加窗插值的DFT方法来估计这一相位偏转值,并对原始待分析的电网信号在频谱直接进行频谱校正,虽然该方法大大地改善电网谐波分析的精度,但对微弱高次谐波分析始终存在较大的频谱泄漏误差。最近提出的时域频谱校正分析方法,由于是利用每根估计谱线的相位来进行校正,这样极易产生相位翻转。本文在利用加窗插值的DFT方法来估计相位偏转值的基础上,不是在频域而是在时域上进行偏转值校正,分析表明:再通过一次对校正后信号的傅立叶变换可以达到减少微弱高次谐波存在大的频谱泄漏误差问题。随后,在此分析的基础上,针对同时包含非整数次和整数次谐波的电网信号进一步研究了更广泛的频谱校正分析法——即在电网中存在非整数倍谐波时,如何进行谐波分析的问题。本文通过构造一个残差滤波器,通过将整数次和非整数次谐波进行分离,对于整数次谐波采取提出的时域频谱校正分析法,对于非整数倍频率分量,在其相位的补偿校正之后,提出了一种利用集合均衡方法进行非整数谐波分析的分析。仿真与实验结果都证明了提出方法的有效性和鲁棒性。
最后,将提出的方法应用于实际的模数转换器(ADC)的动态参数测试。给出了在非同步采样的条件下,进行ADC动态性能参数测试的算法,仿真与实验的结果均证明了该算法的实用性。
Along with the electric power and electronic installation's widespread use in electrical network, the overtone pollution condition is serious day by day. The measurement and analysis of harmonics is the precondition and base of harmonics suppression. Discrete Fourier transform (DFT) is one of the most popular methods applied in computer-based measurement of harmonics signals. However, the non-synchronous sampling, finiteization, and discretization of time-domain and frequency-domain during the spectrum analysis of electric signals cause measuring errors, which makes it difficult to satisfy the request of high detection precision. Therefore, it has important theoretical significance and practical value to engage the research and supplement the remove of harmonic signal spectrum leakage.
This paper firstly analyzes the reason of frequency leakage under non-coherent sampling process, concluding that is caused by the phase variations between the original and truncated signals. Traditional solutions are do corrections on spectrum directly, according to the change phase estimated by the window and interpolation algorithm. This process made great improvement in electric power harmonic spectrum resolution; however, it remains large spectrum estimation error on weak high-order harmonic analysis. The recent FXT method based the phase estimate on compute the phase of every spectral line increase the possibility of phase reversal. The algorithm proposed in this paper firstly gets the phase change by the window interpolation method, and then do phase compensation in time domain instead of the frequency domain. The analysis concludes: the truncated data spectral leakages on high order harmonics are compensated when the corrected data sequence is transformed into the frequency domain by the DFT. Based on the analytical result, the paper extend the target signal to a more wide-use situation: how to do effective harmonic research in actual electric power system when the periodical signal contains both Harmonics and Interharmonics. After building a difference filter, the two different kinds of signals will be departed. For the Harmonics part, the time domain spectral compensation method can be applied. For the Interharmonics part, after the phase correction, a new method named group weighted method was proposed to do the non-integer part of harmonic analysis. Both the simulation and experiment results prove the effectiveness and robustness of proposed approaches.
Finally, the algorithm is used on the application of ADC dynamic parameters test. The test method of ADC dynamic performances under non-coherent sampling process was interpreted in this paper. Both simulation and experiment results verify the practicability and robust of the proposed test algorithm.
引文
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