Detection And Analysis Of Harmonics And Interharmonics In The IEC Standard

Power quality plays a very important role in people’s lives. It is related to the safety and efficiency of the power system and electrical equipment, energy saving, and production and life and the overall efficiency of the national economy. In recent years, with the wide application of various non-linear power electronic devices in power systems, harmonics and interharmonics, as an important indicator of the power quality problems, cause increasingly serious harm to power grids, and the impact on power quality is increasingly prominent. Therefore, harmonics and interharmonics should be controlled without delay. High-precision detection and analysis is the precondition of harmonics and interharmonics control. Aiming at international standard IEC 61000-4-7, the paper is expended through studing the harmonics and interharmonics detection used in the standard. First, the thesis briefly analyzes the theory basis--Fourier transform theory which is recommended by the standard; Secondly, the testing and evaluation methods of the standard are sorted; Finally, the validity of this method is verified through the simulation of the standard method. Meanwhile, the inherent defects of the method are pointed out. Then, aiming at the existing problems in the standard, three different solutions are proposed:(1) A new algorithm of harmonics and interharmonics detection based on Morlet complex wavelet transform is presented in the thesis. First, the paper briefly introduces the theory of wavelet transform. Through the time-frequency characteristics comparison with Fourier transform method, it shows that the algorithm has ability of local analysis, and it theoretically demonstrates that this method can be applied to harmonics and interharmonics detection of the power system simultaneously. Moreover, through the analysis of the wavelet aliasing phenomenon, it shows that the wavelet aliasing is the major bottleneck restricting the development of wavelet in the applications field, and the current workaround of wavelet aliasing problem are outlined. Secondly, the theoretical analysis of the algorithm based on Morlet complex wavelet transform is conducted, and a testing procedure based on the method is provided. Finally, the validity and value of this method in practical applications are verified through simulation and analysis of the typical signal.(2) A new algorithm of harmonics and interharmonics detection based on least squares method is presented in the thesis. First, the paper briefly introduce the theory of least squares method. Secondly, the mathematical derivation to the algorithm is conducted, and the feasibility of this method is demonstrated through mathematical theory and engineering application in harmonic and interharmonic detection. Finally, the validity and value of this method in practical applications are verified through simulation and analysis of the typical signal.(3) A new algorithm of harmonics and interharmonics detection based on empirical mode decomposition (EMD) is presented in the thisis. First, the dissertation briefly introduce the theory of EMD. Through the description of the EMD method, it shows that the algorithm has the advantage as follows:without having a basis function, adaptability, the ability to have a local analysis, no Heisenberg uncertainty principle restrictions, etc, and it theoretically demonstrates that this method can be applied to harmonics and interharmonics detection of the power system at the same time. Secondly, the paper points out the problems of the theory and improved algorithms for these problems are proposed. Finally, the validity and value of this method in practical applications are verified through simulation and analysis of the typical signal.