Study On The Algorithm Of Interharmonics Detection In Power System

Along with the increase of high-capacity loads’ impact and electricity grid connection of a large number of power electronic devices, the complexity of power system harmonic components increases. It is harmful to the electricity grid.Comparing with the traditional harmonics, the frequency of interharmonic is uncertain,which can be any frequency between DC and higher harmonic. This will seriously affect the safety and stability of the power system, and the detection of interharmonics is the premise to inhibit and control it.This paper points out the shortcomings of the IEC standard algorithm, and gives an improved algorithm of the interpolation, the zero filling algorithm and the frequency spectrum correction algorithm. And it is focus on all phase FFT algorithm,with the name "phase invariance", into the detection of interharmonics. The principle of all phase FFT is introduced in detail and an example is given. The theory of spatial spectrum estimation is introduced briefly. The harmonic signal is converted into the spatial domain signal and matrix eigenvalue decomposite based on self correlation through spatial spectrum estimation system, then the signal subspace and the noise subspace are seperated. The paper introduces the principle and process of ESPRIT algorithm and improved algorithm, MUSIC algorithm and its improvement.Not only the all phase FFT and TLS-ESPRIT are explained, but also the advantages and disadvantages of them are analyzed, which provides a good condition for the proposed algorithm. The all phase FFT has a good phase detection function,the phase does not change with the frequency deviation. However, when the frequency of harmonics is closed to that of the interharmonics, the all phase FFT frequency resolving ability is worse than the TLS-ESPRIT algorithm, The TLS-ESPRIT algorithm can deal with the closed frequency problem, but its calculation is complex and it is unable to detect the phase and amplitude. This paper makes full use of the advantages of both, and proposes a comprehensive algorithm for the all phase FFT and the TLS-ESPRIT. The comprehensive algorithm proposed in this paper can not only ensure the accuracy of phase and frequency detection, but also can reduce the amount of calculation to some extent and accelerate the speed of calculation. Besides, the simulation examples verify the effectiveness and superiority of the algorithm.