Double-Synchronous-Reference-Frame-Based Power-Synchronized PLL-Less Grid-Following Inverters for Unbalanced Grid Faults

This article proposes a double-synchronous-reference-frame-based power-synchronized grid-following inverter (DS-PSGFLI). In contrast to existing types of phase-locked-loop (PLL)-based inverters (GFLIs) and PLL-less GFLIs (PSGFLIs), the suggested DS-PSGFLI operates seamlessly during unbalanced grid faults in both strong weak connections, while maintaining stability avoiding oscillations. Furthermore, unlike previous control strategies for PSGFLIs that regulate terminal output power, proposed method regulates power at point common coupling (PCC). approach aligns with PCC grid-forming inverters, thereby impacts voltage drop across filter high harmonics terminal. DS-PSGFLI, positive negative sequences current measurements are first extracted. Then, an outer controller is employed active reactive desired references. The generates internal angle required synchronization reference inner sequence loop. When occur, loop adjusts its signals mitigate resulting oscillations twice fundamental frequency. effectiveness strategy validated through simulations experimental tests, demonstrating reliable performance wide range test scenarios.