【作者】 温和；

【导师】 滕召胜；

【作者基本信息】 湖南大学 ， 控制科学与工程， 2009， 博士

【摘要】 谐波的准确检测是研究电力系统谐波问题的重要内容,为谐波潮流计算、绝缘设备检测、谐波电能计量、谐波补偿与抑制等提供科学依据。基于快速傅里叶变换(fast Fourier transform,FFT)的谐波分析方法易于嵌入式系统实现而应用广泛。然而,非同步采样情况下直接采用FFT进行谐波分析时,受频谱泄漏和栅栏效应影响,谐波参数检测准确度较低。因此研究新型窗函数与改进FFT谐波分析方法,并将其在嵌入式系统中实现,对提高谐波检测准确度和实时性具有重大的理论和现实意义。本论文针对电力系统谐波检测中存在的问题,提出了系列新型窗函数及改进FFT谐波分析方法,研究内容主要包括:1)三角自卷积窗、余弦卷积窗和梯形自卷积窗及基于上述窗函数的改进FFT谐波分析方法;2)改进FFT谐波分析方法在谐波电能计量、介损角测量中的应用。论文首先分析了影响FFT谐波分析准确度的关键因素,从改善窗函数、充分抑制频谱泄漏的角度,提出并建立了三角自卷积窗及其改进FFT谐波分析方法。三角自卷积窗由三角窗进行时域自卷积运算获得,其频谱泄漏抑制能力随卷积次数的增加而迅速增强。基于三角自卷积窗的改进FFT谐波分析方法通过对离散频谱的局部峰值搜索,确定谐波频率附近的幅度最大和次大谱线,再根据两根峰值谱线的比值,并利用基于最小二乘多项式拟合方法,得到离散频谱频率偏差插值多项式和谐波参数计算式。仿真研究表明,三角自卷积窗旁瓣性能优良,可有效减少谐波对基波的泄漏干扰,提高了基波参数提取的准确度,且具有较强的抗干扰能力。其次,论文利用余弦组合窗的优良旁瓣特性,提出并建立了余弦卷积窗,定义了余弦混合卷积窗和余弦自卷积窗,建立了余弦卷积窗的时频特性。余弦卷积窗的主瓣宽度与参与卷积的余弦组合窗中主瓣最窄的窗相同;余弦卷积窗的旁瓣衰减速率等于参与卷积的各窗的旁瓣衰减速率之和;余弦卷积窗的旁瓣峰值电平出现在参与卷积的余弦组合窗中主瓣最窄的窗的旁瓣峰值电平处,且等于参与卷积的各窗在该处的幅度值之和。余弦卷积窗的时频特性研究为进一步深入研究基于余弦卷积窗的改进FFT谐波分析方法提供了理论依据。论文以Hanning窗为例,提出并建立了Hanning自卷积窗及其改进FFT谐波分析方法,建立了基于Hanning自卷积窗的离散频谱相位差校正算法。与三角自卷积窗相比,Hanning自卷积窗旁瓣性能优越,抑制频谱泄漏能力强;基于Hanning自卷积窗的改进FFT谐波分析方法提高了谐波分析的准确度,特别适合于高次谐波分量、弱幅值谐波分量的分析。随后,在提出三角自卷积窗和余弦卷积窗的基础上,论文提出并建立了梯形自卷积窗,分析了梯形自卷积窗时频特性,建立基于梯形自卷积窗的改进FFT谐波分析方法。论文一方面通过调整系数优化梯形窗主瓣与旁瓣性能,另一方面采用时域卷积方法使其旁瓣性能得到进一步提升。与三角自卷积窗和Hanning自卷积窗相比,梯形自卷积窗更适合于频率分辨率要求较高的场合,如间谐波分析等。最后,利用Hanning自卷积窗、三角自卷积窗分别适合于高次谐波分析、基波参数提取的特点,论文将所提出的改进FFT谐波分析算法应用于谐波电能计量、介损角测量中,提出了基于Hanning自卷积窗的谐波电能计量算法和基于三角自卷积窗的介损角测量算法,并利用嵌入式系统平台实现了谐波电能计量与介损角测量,研究出了基于数字信号处理器的三相多功能谐波电能表和介损角测量终端。三相多功能谐波电能表可实现高准确度谐波电能计量和实时谐波分析,谐波存在时有功电能计量达到0.2S级,且完全满足GB/T-14549-93的A类谐波测量仪器要求。介损角测量终端的仿真与模拟实验结果表明其测量结果准确度高,为进一步介损角实际测量提供了有力保证。更多还原

【Abstract】 The accurate harmonic analysis of power system is an important task for the research of harmonic pollution, which is also the basis for the identification of excessive harmonic flow, diagnosis of high voltage insulation, measurement of harmonic electric energy, compensation and suppression of power harmonic. The FFT is the most commonly used technique for power system harmonic analysis because of its simplicity and easy implementation in embedded system. However, the direct application of FFT for harmonic analysis may lead to inaccuracies due to the spectral leakage and the picket-fence effects with asynchronous sampling. Hence, it is of great theoretic and practical importance to study and implement novel FFT-based methods for accurate and real-time harmonic analysis.This dissertation proposes new kinds of windows and improved FFT-based harmonic analysis methods, especially on the Triangular self-convolution window (TRISCW), the cosine-combined convolution window(CCCW), the Hanning self-convolution window(HSCW), the Trapezoid self-convolution window(TRASCW), the improved FFT-based harmonic analysis methods with these proposed windows, the application of the proposed methods in harmonic electric energy measurement and dielectric loss angle online measurement.Firstly, the key factors of the FFT-based harmonic analysis method are analyzed. The TRISCW is proposed, which is constructed by self-convolutions of the Triangular window in time domain. With the increase of the self-convolution times, the spectral leakage can be more efficiently suppressed by using the TRISCW. The improved FFT-based harmonic analysis method based on the TRISCW is presented, where the harmonic parameters are calculated by spectral interpolation accurately.Then, the CCCW is proposed, and the cosine-combined cross-convolution window and the cosine-combined self-convolution window are defined and studied. The CCCW has the same major lobe width with the window who is one of the original window and also has a narrow major lobe width. The peak side lobe level and side lobe roll-off rate of the CCCW are the sum of the original windows. The study of the CCCW paves the way for the FFT-based harmonic analysis with the CCCW.This dissertation takes the Hanning window for example, proposes the HSCW and the improved FFT-based harmonic analysis method. The HSCW has a low peak side lobe level, a high side lobe roll-off rate. Hence, leakage errors and harmonic interferences can be considerably reduced. The improved FTT-based harmonic analysis method with the HSCW achieves better performance for applications where the spectral leakage is a main problem, such as the weak harmonic analysis of power system.Subsequently, based on the proposed TRISCW and CCCW, the TRASCW is proposed. The Trapezoid window is optimized by adjusting the window parameters, and the TRASCW with better sidelobe behavior is then obtained by self-convolutions in time domain. The TRASCW has narrow major lobe width, which makes it suitable for applications where the high frequency resolution is required, such as the inter-harmonic analysis.Finally, the proposed FFT-based harmonic analysis methods are implemented to the harmonic electric energy measurement and dielectric loss angle measurement. The harmonic electric energy measurement algorithm based on the HSCW and the dielectric loss angle measurement algorithm based on the TRISCW are proposed and realized in the embedded system, i.e. the digital signal processor. The testing and application results show that the three phase multi-function harmonic power energy meter achieves a precision of grade 0.2S for electrical power measurement, and completely fulfills the requirements for class A power harmonics measurement stated in GB/T14549-1993 Power Quality, Harmonics in Public Power Grid, the terminal can perform high accuracy of the dielectric loss angle online measurement, which can provide a basis for further practical application.更多还原