Abstract
ABSTRACTThe fast Fourier transform (FFT) algorithm with window interpolation is the most commonly used and most effective method in harmonic analysis. However, the fast Fourier transform has a great dependence on the quality of the signal, and the existence of noise makes the detection result error. A harmonic detection method based on wavelet threshold preprocessing noise elimination and windowed interpolation FFT algorithm is proposed in this thesis. Firstly, de-noising the selected signals, and the wavelet coefficients are used to select the wavelet threshold to eliminate the noise in the signal. Then the signal after the de-noising is analysed by the Nuttall window interpolate FFT algorithm, and the calculation formula is derived by using the amplitude information content of four spectral lines. The simulation results show that the proposed method is more accurate and effective to detect the signal after de-noising.
Highlights
With the interconnection of power systems becoming more and more complex, a large number of nonlinear loads cause the harmonic pollution serious and complex in the power grid
A harmonic detection method based on wavelet threshold preprocessing noise elimination and windowed interpolation fast Fourier transform (FFT) algorithm is proposed in this thesis
The Nuttall window interpolation FFT algorithm is used for analysis, and the correction formula is derived from the weighted operation of the four spectral lines, which effectively utilizes the spectrum information, suppresses sidelobe leakage, and reduces the error caused by the fence effect
Summary
With the interconnection of power systems becoming more and more complex, a large number of nonlinear loads cause the harmonic pollution serious and complex in the power grid. The signal processed by window function can effectively compensate for the spectrum leakage (Zhang, He, & Zang, 2017) and the fence effect when the harmonic parameters are analysed (Chen, Chen, & Cai, 2011; Lan, Li, & Wang, 2009; Li, Li, & Yang, 2017; Zeng, Tang, & Qing, 2014). The double-spectrum interpolation algorithm uses the two spectral lines near the peak spectral frequency to obtain the harmonic parameters by introducing the frequency offset, but the algorithm does not fully take advantage of the information of the leakage line near the frequency (Qing, Teng, & Gao, 2009). The Nuttall window interpolation FFT algorithm is used for analysis, and the correction formula is derived from the weighted operation of the four spectral lines, which effectively utilizes the spectrum information, suppresses sidelobe leakage, and reduces the error caused by the fence effect
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