Research On The Application Of The Spectrum Analysis Theory In The Detection Of Harmonics And Inter-harmonics

In recent years, along with the extensively application of the power electronic technology, the pollution of the harmonics becomes more and more seriously and it influences the electric power quality seriously. As a result, harmonics and inter-harmonics problems have attracted widespread attention.Firstly, this paper introduces the derive, harm and lots of detection algorithms of harmonics and inter-harmonics, analyses the advantage and disadvantage of every algorithm, and then details the Fourier transformation theory and the theory of modern spectral estimates, which elucidates the research background.Secondly, this paper details the basic theory of Fourier transform, and the problems which must be paid attention to in the practical application. The reasons of the error caused by the traditional electric signal detection methods based on the windowed DFT are thoroughly analyzed. Besides, many cosine windows are introduced.Based on the spectrum correction theory, we propose an algorithm which is suitable for harmonics and inter-harmonics measuring. The simulation of the Matlab proves that the algorithm can meet the demand of harmonics and inter-harmonics detection when choosing suitable length of data window, sampling frequency, and corresponding windows. However, this algorithm is not fit for the detection of the signals whose frequencies are very close to each other.Therefore, using the AR model and the Prony model to measure the inter-harmonics, an inter-harmonics measuring algorithm which is based on advanced spectral estimation is presented. Because of the spectral line splitting of the Burg algorithm, the recursive algorithm of the AR model, we choice the Hamming weighted Burg algorithm in this paper. The modified Burg algorithm can weaken the spectral line splitting effectively. However, the AR model can't gain the phase of the inter-harmonics. So the Prony model is adopted to detect the inter-harmonics. Although the Prony model can achieve high precision, it is much more sensitive to noise and can be applied only under the higher SNR circumstance. The studying results show that the advanced spectral estimation is more predominant than DFT algorithm and its corrected algorithms in the field of inter-harmonics measuring, especially for the inter-harmonics which is too close to harmonics. Hence, it is effective and feasible to introduce the advanced spectral estimation into inter-harmonics measuring.