Frequency Fluctuations in Marine Microgrids: Origins and Identification Tools

Fluctuation of frequency IS arguably the most characteristic feature of marine microgrids. T his concerns both frequency drift during step load change and all quasi-periodic fluctuation due to the impact of various factors like generators' prime movers, the governor's characteristic, and sea conditions. This article aims to provide insight into the latter phenomena. Such quasi-periodic frequency fluctuations can have detrimental effects on electrical receivers' work, especially electric motors. For the study of these fluctuations, the use of time-frequency (TF) analysis methods is the most natural choice. Among TF analysis methods, the Hilbert?Huang transform (HHT) offers some advantages to analyze signals with multiple frequency components. It is well suited for nonlinear and nonstationary signals as it estimates the instantaneous frequency of the signal, which is defined locally as the time derivative of the signal phase. The zoom discrete Fourier transform (zoom-DFT) is another method that can provide an instantaneous frequency representation of the signal using spectral zoom operation [usually a chirp z transform (CZT) method is used] and with that can portray quasi-periodic frequency fluctuations, should they exist.