The Application In Detection Of Power Quality Disturbances Based On STFT And S-transform

In recent years, with the increase of nonlinear impact load in grid and frequency control devices, it results power quality problems such as grid interruption, voltage fluctuations,voltage sags, and harmonics in voltage distribution have become more and more serious. In order to suppress and control power quality problems, the device must be added to compensate for the power quality in the grid, development and tuning of these devices require accurate, detailed power quality parameters. Therefore, understanding the mechanism of the disturbance signal, accurate detection of the characteristic parameters of signal disturbance(including amplitude, frequency, start and end time, phase, etc.), and the disturbance signal classification play a very important role in improving the quality of power supply and ensuring the safe operation of the power system.This research is based on transformation approaches to detect a variety of power disturbance signals. Firstly, it uses short-time Fourier transform to detect harmonic signal, and to obtain the defect of short time Fourier transform from the analysis. then it uses Stransform method to detect power quality Problems such as typical harmonic signal, voltage fluctuations and flicker, voltage swells and voltage sag and two composite signals. during the Matlab simulation, 50 db white Gaussian noise is joined in the disturbance signals., from which to simulate a variety of signals to obtain the corresponding amplitude-frequency curve, phase frequency curve, and time-frequency distribution of them. In addition, it extracts their various curves characteristic values and selects the best combination of characteristic values, using SVM(support vector machine) algorithm for power quality disturbance signal automatic classification to make the classification accuracy to achieve the best.In terms of hardware, signal conditioning circuit is designed according to the system of PCI8620 data acquisition card, using CLF call dynamic link library to achieve the connection of non-NI’s data acquisition card and Labview. Program design uses FFT algorithm to calculate the amplitude of the signal acquisition and other contents and describes how to call Matlab in Labview program. Experimental measurements demonstrate that the system design is reasonable and effective, in line with the relevant national standards.