An implementation of Short Time Fourier Transform for Harmonic Signal Detection

Abstract

Power electronic components has the tendency to induce a non-linear signal called harmonic distortion. Without proper monitoring tools, harmonic distortion can harm sensitive electronic equipment, and in worse case scenarios, may lead to unreliable operation of controller and misalignment of motoring unit. This matter can be compromised by taking safety precaution, by identifying the level of harmonic rise in the electrical system. This paper presents analysis on different characteristics of harmonic signal using frequency distribution technique, namely Fourier transform (FT), and proposal of time-frequency distribution (TFD) technique, which is a short time Fourier transform (STFT). The novelty of utilizing STFT is the analyzed signal is represented in both time and frequency marginals, hence providing extra information of the spectral over the time. Simulation was carried out using MATLAB, by means the results consisting of the magnitude of multi-frequency components signal were represented in time-frequency representation (TFR). From the TFR, parameters such as instantaneous RMS fundamental voltage, V1RMS(t), instantaneous RMS voltage, VRMS(t), instantaneous total waveform distortion, VTWD(t), instantaneous total harmonic distortion, VTHD(t) and instantaneous total nonharmonic distortion, VTnHD(t) had been extracted. The performance of different harmonic signals such as normal, single-level harmonic, multi-level harmonic, short duration harmonic and interharmonic had been analyzed. The performance based on absolute percentage error (APE) index indicated average of 93% of correctness using 256 window length in STFT measurement.