【作者】 张超；

【导师】 王维庆；

【作者基本信息】 新疆大学 ， 电气工程， 2019， 硕士

【摘要】 新能源风力发电中广泛使用的电力电子装置会产生次同步谐波,严重影响电网电能质量。此外,可能导致火电机组发生轴系扭振,造成轴系损坏,危害整个电力系统安全稳定运行。故精确地检测出次同步谐波分量具有重要意义。常用的次同步谐波分析方法是快速傅立叶变换(fast Fourier transform,FFT),对信号进行离散分析时因非同步采样和非整数周期截断导致频谱泄露和栅栏效应现象,因此利用谱线信息难以高精度检测谐波各参数。针对此现象,加窗插值算法和全相傅里叶变换(all-phase FFT,ap FFT)可以提高参数估计的精确度。本文在对经典纳托尔窗(Nuttall)频谱特性分析的基础上,提出以4项5阶Nuttall窗通过自卷积运算得到1-4阶Nuttall自卷积窗(Nuttall self-convolution window,NSCW)函数。自卷积窗函数与经典窗函数相比,具有更加优良的旁瓣特性,能进一步减少频谱泄露。基于主瓣与旁瓣特性的综合考虑,选用4阶NSCW函数对信号进行截断。结合四谱线插值法原理,推导出基于自卷积窗的四谱线插值校正公式。因ap FFT具有“相位不变性”,利用理论频点附近主谱线与旁谱线幅值比值,推导出基于Nuttall双窗ap FFT双谱线插值频谱校正算法。加窗插值FFT算法针对幅值及频率参数具有较高估计精度,ap FFT能够有效提取相位参数。由此提出将前者用于幅值和频率检测,后者用于相位检测的组合优化算法。将本文算法与基于经典窗的谱线插值FFT算法分别用于电力谐波信号分析,并在信号存在噪音干扰和频率波动影响情况下,验证本文所提方法测量谐波参数的准确性。通过MATLAB仿真分析表明,该算法能较精确地检测次同步谐波的频率特征值并抑制谱间干扰,且在分析谐波的幅值、相位及频率参数时精度较其他算法有数量级提高。在噪音干扰和频率波动时,本文组合优化算法测量谐波参数时受影响较小,仍具有高的测量精度。最后,将组合算法应用于新疆地区次同步谐波检测,并与加Hanning窗及Nuttall窗谱线插值FFT算法进行对比分析。仿真结果表明,本文算法能够有效并高精度实现次同步谐波检测功能。更多还原

【Abstract】 Subsynchronous harmonics will be generated in power electronic devices widely used in new energy wind power generation system.Subsynchronous harmonics severely affect the power quality of the power grid,and it may lead to shafting torsional vibration of thermal power units,resulting in shafting damage and even endangering the safe and stable operation of the whole power system.Consequently,giving great significance to accurately detecting subsynchronous harmonics components.The commonly used subsynchronous harmonic detection method is fast Fourier transform(FFT),whereas,the spectrum leakage and fence effect are caused by asynchronous sampling and non-integer period truncation in discrete analysis of signals,so it is difficult to detect harmonics with high precision by using spectral information.For this phenomenon,the utilization of windowed interpolation algorithm and all-phase FFT(ap FFT)can improve the accuracy of parameter estimation.Based on the analysis of the spectrum characteristics of classical Nuttall window,1st-4th order Nuttall self-convolution window functions are obtained by several 4 terms 5 order Nuttall window self-convolution operations.Compared with classical window functions,self-convolution window functions have better side-lobe characteristics and can further reduce spectrum leakage.Based on the comprehensive consideration of the main-lobe and side-lobe characteristics,the 4 order Nuttall self-convolution window function is used to truncate the signal.According to the principle of quadruple-spectrum-line interpolation,the rectification formula of the 4th order Nuttall self-convolution window function is proposed.According to the phase invariance of ap FFT,the double-spectral-line correction harmonic analysis algorithm based on Nuttall double window ap FFT is deduced by using the ratio of the main spectral line and side spectral line amplitudes near the theory frequency point.The windowed interpolation FFT algorithm has higher estimation accuracy for amplitude and frequency parameters,and ap FFT can effectively extract phase parameters.A combinatorial optimization algorithm is proposed,which uses the first method to detect amplitude and frequency parameters,and uses the second method to detect phase parameter.The combinatorial optimization algorithm and the interpolation FFT algorithm based on classic window functions are used to analyze power harmonic signals respectively,and the accuracy of measuring harmonic parameters is validated under the influence of noise interference and frequency fluctuation.MATLAB simulation analysis indicates that the algorithm can detect the frequency eigenvalues of subsynchronous harmonics more precisely,and suppress the interference between the spectrums.The accuracy of the amplitude,phase and frequency parameters of the harmonic is increased by orders of magnitude compared with other algorithms.In the case of noise interference and frequency fluctuation,the combined optimization algorithm has less influence on the measurement of harmonic parameters,and still has high measurement accuracy.Finally,the combinatorial optimization algorithm is applied to the subsynchronous harmonic detection in Xinjiang,and compared with the Hanning windowed and Nuttall windowed interpolation FFT algorithm.The simulation results show that the algorithm can effectively and accurately achieve subsynchronous harmonic detection purposes.更多还原