Enhanced Seamless Transition Control of Grid-Tied Converters Using Dual-eSOGI Vector-Based Synchronization Under Grid Faults

This article proposes a vector-based synchronization (VBS) technique using dual-enhanced second-order generalized integrator (eSOGI) for seamless transitions between grid-connected (GC) and standalone (SA) modes. Conventional methods, such as synchronous reference frame phase-locked loops, suffer from slow response and inaccurate voltage estimation during voltage sags, leading to long transients. The proposed VBS using the dual-eSOGI method enables faster and more accurate voltage estimation. An angle alignment method is introduced for presynchronization to enhance performance, minimizing phase mismatches, and frequency transients between the SA and GC transitions. Simulation results on a 1-MW system demonstrate that the proposed method reduces the load fluctuation from 25.75% to 6.89% during unbalanced voltage sag in GC to SA mode transitions and shortens the transition time by 42.26% in SA to GC modes compared to conventional methods. Experimental results on a 1-kW setup validate its effectiveness, demonstrating a stable load current with minimal disturbances.