Analysis of transient waveform based on combined short time Fourier transform and wavelet transform

Transient harmonics can be analyzed by short time Fourier Transform (STFT) and wavelet transform respectively. However, there are disadvantages in both of them. The former cannot have favorable result except for having a suitable window, and the latter cannot acquire single harmonic frequency and its amplitude. After comparing the advantages and disadvantages of STFT and wavelet transform which are used to analyze signal of transient harmonic in power system, combining their merits, a novel STFT based on the special frequency band is proposed in this paper. Multiresolution analysis is used to detect the fault time and determine the main frequency range of transient signal. Then the central point and proper width of window of STFT can be obtained. Consequently the accuracy and efficiency of STFT can be improved greatly, frequency components and its amplitudes of transient signal can be obtained accurately and quickly by this method. An on-line system to inspect and analyze transient waveform is designed based on LabVIEW, through which the feasibility and the accurateness of this method have been verified.