Comparative analysis of time-frequency transform-based differential protection strategy for distributed generation integrated microgrid

This study presents a differential protection strategy for distributed generation-integrated power systems. It explores and compares two enhanced traditional signal processing methods: the Hilbert-Huang Transform (HHT) and the S-transform. The HHT has been improved by incorporating Variational Mode Decomposition (VMD), while the S-transform has been augmented with a Fourier component to create the Fast Fourier Discrete Orthonormal Stockwell Transform (FFDOST). VMD and FFDOST are applied to three-phase current signals from microgrid buses to calculate the Spectral Energy (SE). Fault detection is based on Differential Energy (DE), which measures the difference in SE between two specific faulty buses, with a tripping signal activated when DE surpasses a predetermined threshold. The effectiveness of this approach is rigorously tested and validated on a typical DG-integrated microgrid that includes synchronous generators and wind farms. A comprehensive set of case studies conducted on an IEC microgrid model examines various fault types (symmetrical and asymmetrical) across different operational modes (islanded and grid-connected) and configurations (radial and looped) under varying noise conditions. The performance of these two modified differential strategies is critically compared to determine the more effective method. Detailed sample-wise analysis and graphical presentations enrich the documentation of results. The VMD-based method outperforms the FFDOST approach, detecting faults 3 to 15 samples sooner and achieving quicker fault detection by approximately 0.05 milliseconds. Comparative analyses suggest that VMD is a faster, more secure, and highly reliable method for fault detection and mitigation, enhancing microgrids' operational security and reliability.