Voltage Sags Source Location Based On Modified Incomplete S-transform

With a large number of the high penetration distributed power and high-speed rail impact loads connect to power grid,power quality problems of distribution network become increasingly prominent.Power quality is one of the most serious problems.Quickly and accurately identify voltage sags source and location of voltage sags source are helpful to implement the voltage sags compensation.Firstly,on the basis of analyzing and summarizing the research status of voltage sags identification,further discussing the mechanism of voltage sag and analysis the waveform characteristics of different types of voltage sag.The standard S-transform has the problem that the Gaussian window shape has the invariance and computation of all the frequency points,it is difficult to meet the requirements of the voltage sag signal at different time bands with multi-resolution.Therefore,this paper improves the Gaussian window function of S-transform on the basis of standard S transform,introduces a frequency-dependent variable factor,combines the modified S-transform with the Dynamics,and proposes an modified incomplete S-transform to realize the voltage sag signal amplitude,start and end time,harmonic content and other characteristics of rapid and effective detection.Simulation results indicate that the improved incomplete S-transform has better performance than the S transform.Then,in order to further make full use of the frequency characteristics of the voltage sag signal and realize the accurate judgment of the voltage sags source,proposes voltage sag source identification method combining improved incomplete S-transform and template matching.Using 50 random waveforms of different types of voltage sag signals to improve the incomplete S-transform and standard templates established by scale transform,analysis the similarity between the specific region of the matrix of the test signals and the standard templates.The signals could be classified in accordance with main frequency of signal and the principle of maximum similarity.Next,simulation of various types of voltage sag signals with 20,30,40 dB Gaussian white noise,simulation results indicate that the proposed method can quickly and accurately identify the source of the disturbance caused by voltage sags,without extra classification process,low computational complexity and high accuracy and noise robustness.Finally,on the basis of realizing the classification of voltage sags,the short-circuit fault type of voltage sag source is identified,this paper proposes a faulted phase selection scheme using waveform characteristic of single-mode current.The use of three-phase current and its combined current and mode 1 current waveform cross correlation characteristics to achieve fault phase identification.A typical model of voltage sag simulation system of distribution network is established in PSCAD,which verifies he proposed method is correct and effective in different working conditions,the proposed method on which the phase voltage sag compensation is based.