关键词: 傅里叶变换, 谐波与间谐波检测, 栅栏效应, 频率偏移偿相频特性

Abstract: The wide use of nonlinear components in power system produces integer and non-integer harmonics in the electrical power system. The conventional harmonic measurement algorithm-Fast Fourier Transform(FFT) is suitable for harmonic analysis under synchronized sampling condition, but is not capable to analyze non-integer harmonics due to its leakage effect. The leakage of FFT algorithm is caused by the different characters between the theoretic implementation of the Fourier Transform which deals with infinite signals and the practical implementation of Fourier Transform which deals with finite signals. The differences give rise to the measurement errors of inter-harmonics of FFT algorithm. In order to overcome the leakage effect of FFT algorithm, a new desynchronized signal processing technique is proposed, which is based on poly-item cosine window(CW) interpolation. The general expression of parameter estimation by K-item cosine window is obtained. Generally, extensive simulation results are provided to verify the validity and effectiveness of the proposed algorithm based on rectangular window and hanning window, which reveals that the frequencies, amplitudes and phase angles of the harmonics and the inter-harmonics are accurately calculated, even under significant fundamental frequency deviations in the input signal by adopting hanning window interpolation. Moreover, the proposed technique is found to have overwhelming advantages in terms of the improved estimation accuracy and the reduced computational burden compared to the existing unsynchronized sampling techniques in literature.

Key words: fast Fourier transform, harmonic and inter-harmonic detection, leakage effect, deviation