Analysis of Power System Harmonic Subgroups of the Electric Arc Furnace Currents Based on a Hybrid Time-Frequency Analysis Method

In this paper, a hybrid time-frequency analysis method is developed to extract the time domain waveform of the harmonic subgroups of the electric arc furnace (EAF) currents so as to serve as reference signals for the active power filters to suppress highly time-varying harmonics and interharmonics being eventuated in power systems by the EAFs. Contrary to classical frequency analysis, in this work, the aim is the detection of harmonics and interharmonics subject to fast changes or sudden events in power system signals. Discrete Wavelet Transform (DWT) based methods have been investigated and utilized in harmonic decomposition operations in many studies carried out so far. Despite being useful at low frequencies, in DWT bandwidth of the analysis bands increases and hence frequency resolution decreases at high frequencies. In this study, to overcome this inefficacy, power signals are modified by a complex exponential modulation technique, which corresponds to shifting harmonic contents to lower and higher frequency bands. With the combination of the modulation with wavelet decomposition, time domain waveform of each frequency band of the EAF currents, which are rich in time-varying harmonics and interharmonics, can be estimated almost ideally. The proposed harmonic and interharmonic estimation method has been verified on both synthetic data and EAF currents collected from the electricity transmission system. Estimated harmonic and interharmonic waveforms can serve as a good reference in many areas including active power filtering operations, limit violation determinations, and etc. in the power system.