Study On Detection Method Of Power Grid Interharmonic Based On Subspace Decomposition

With appear in large number of of nonlinear,fluctuation and impact load in powersystem,there are not only harmonic whose frequency is integer times of powerfrequency exist in the power grid,but also frequency components whose frequency isnot integer times of power frequency, namely interharmonic. Harmonic and inter-harmonic bring more and more serious pollution to power network, and caused harm tothe safe, reliable and economic operation of the power system so they must bemanagemed. Accurate detection of parameters of harmonic and inteharmonic is theprerequisite to realize effective governance.Detection methods of interharmonic both at home and abroad After weresummaried and analysised in this article, and analyzes modern spectrum analysis withhigh resolution, put forth the subspace decomposition method to detection inteharmonicparameters of power grid based on the spatial spectral estimation principle. Subspacedecomposition method divide the observation data matrix from the sampling data intoand noise subspace. Noise subspace algorithm and signal subspace algorithm make useof the characteristics of noise subspace and signal subspace respectively, they areMUSIC algorithm and ESPRIT algorithm.After analysis of estimate principle of MUSIC, this paper uses traditional MUSICand Root-MUSIC to estimate interharmonic parameters of power grid, then analysis andimprove the key problems of solving process. In view of characteristics of real samplingsignal of actual power grid, puts forward the real realization forms of Root-MUSICbased on real-valued MUSIC. After analysis of several least squares estimating methodsof amplitude and phase, the method of real-valud Root-MUSIC combined with Pronycan greatly reduce computation cost, improve the estimation precision. Through thesimulation analysis, comparison and verify the estimated performance of interharmonicparameters of MUSIC and the improved method.Based on the idea of ESPRIT algorithm, we use the basic ESPRIT, LS-ESPRITand TLS three methods to realize estimation of interharmonic parameters of power grid,this paper analyzes the matrix calculation and characteristic value or singular valuedecomposition times of three methods, put forward improvement ESPRIT with only aeigenvalue decomposition used in analysis of inter harmonic, simulates the influence of the number of array and noise to estimate accuracy of interharmonic parameters ofseveral ESPRIT methods, and validates the real-time and effectiveness of improvedmethod.Real-valued Root-MUSIC and TLS-ESPRIT with better estimation performance intwo kinds of subspace decomposition methods are detailed analysis, it is provedaccuracy of using AIC criterion to estimates the number of source with lowsignal-to-noise ratio in this paper, thus noise subspace and signal subspace can bedivided accurately, simulates the influence of noise, sampling number and array numberto estimation precision of two subspace decomposition methods, the estimationaccuracy of two methods increases with the number of samples, and TLS-ESPRIT ismore sensitive to sampling number.It is not need whole cycle sampling to signal forsubspace decomposition method.Improved subspace decomposition method has higherfrequency resolution, and low computing complexity with smaller hits.It is providedwith better application research value.