Measurement Of The Power System Interharmonics Based On Higher-order Statistics And The Applied Research

Interharmonics in power system is a kind of the harmonics which are not an integer multiple of the fundamental frequency component. The interharmonics makes the induction motor noisy and vibrative, causes voltage flicker and worsens the power quality, so it is important to measure accurately.Higher-order statistics (HOS) have been received increasing interest in the field of signal process both at china and abroad. The HOS describing the signal higher order digital characteristic, can solve the problems of non-Gauss and non-linear, and may suppress the influence of Gauss colored noise completely,therefore can be used to process noise problems of interharmonics detection.This thesis introduces the HOS firstly, and mainly focuses on the higher order moment ,higher order cumulant and higher order cumulant characteristic in Gauss process, then it analysis several commonly properties and the estimate methods.Secondly, it explains the power spectrum estimate theory in details: parameter estimation method and non-parameter method. The parameter estimation mainly includes several kinds of commonly used parametric model establishment and the solution method, such as AR model,ARMA model. The non-parameter estimate mainly includes the decomposes frequency estimate theory based on the eigenvalue decomposition. Finally the multi-signal classification (MUSIC) computational method is proposed in detail.Based on the higher order cumulant characteristic, this thesis uses the fourth-order cumulant definition the matrix to instead on the traditional second-order statistics matrix, then it presents the linear prediction method and the MUSIC method based on the fourth-order cumulant. The simulation experiment and the computed result indicates that the new method may estimate parameter precisely, and can suppress the Gauss noise effectively, thus it provides one effective method for the electrical power system interharmonics measure.On the basis of interharmonic research, this paper analyzes the characteristic of the recovery voltage when single phase earth fault occurs in EHV/UHV transmission line with shunt reactor. The results show that recovery voltage of temporary fault contains the components of power frequency component and free component, while the recovery voltage of permanent fault only contains power frequency component. According to the different frequency characteristics of recovery voltage, using the distribution of spectral line nearby the power frequency in power spectrum to distinguish the temporary faults. The simulations results show that the proposed method is exact and feasible.