Multi-Synchrosqueezing Transform-Based Hybrid Method for Frequency Components Detection of Nonstationary Voltage and Current Waveforms

Harmonics, inter-harmonics, and low-frequency (below the fundamental frequency) components produced by nonlinear loads and renewables may cause undesired effects on electric power equipment including overheating, resonance, and voltage flickers. This paper presents a hybrid method for the detection of frequency components of the measured waveform that is nonstationary (time-varying) in a holistic manner. In the proposed method, the multi-syncrosqueezing transform (MSST) is firstly applied to determine time-frequency ridges for the low-frequency, fundamental, harmonic, and interharmonic components. Next, the algorithm of density-based spatial clustering of applications with noise (DBSCAN) is adopted to precisely identify the prominent frequency components (i.e., intrinsic modes) using the MSST results. The time-domain waveforms corresponding to each detected frequency component and the original signal are then reconstructed via the inverse operation of MSST to assess the rms, and total harmonic and interharmonic distortion (THD and ITHD) trends of the recovered waveforms. The proposed method is validated by simulations and actual measurements to show its usefulness. Results are also compared with different time-frequency analysis methods to show the superiority of the proposed method.