Tool for detecting waveform distortions in inverter-based microgrids: A validation study

摘要

This paper presents a validation methodology based on data analysis aimed at identifying the cause of atypical behavior observed in a microgrid's data. The data of a standalone PV microgrid in Bhutan is used for the analysis. Voltage waveform distortions observed in the data were analyzed by utilizing the Hilbert-Huang Transform (HHT) and the discrete Fourier transform (DFT). When using HHT, a time-varying frequency, new to electrical systems, is revealed by the microgrid data analysis, while the mathematical derivation hints on amplitude modulation. The distortions appeared in the form of a leakage spectrum composed of multiple numbers of constant frequency components when using a DFT-based frequency power spectrum. The different observations from these methods have raised questions of interpretation of their physical meaning. In an attempt to provide a physical meaning and to understand the cause of the time varying frequency revealed by the HHT, an analytical investigation of the micro-grid controller is performed. The results obtained indicate that modern power electronics introduces new types of distortions that can be traced back to the control of the inverters in the microgrid. The analytically obtained results compared with the analysis of simulated and field measurements hint on the existence of a time-varying frequency in the voltage waveforms of the stand-alone microgrid. The results of this paper will lay the foundation for future studies into more accurate diagnosis tools for microgrids to enable affordable access to electricity in isolated communities.