Transient Stability Analysis and Control of PLL-Synchronized Grid-Connected Inverters for Low-Voltage Ride-Through

Abstract: (This webinar is sponsored by PELS Young Professionals) As renewable energy sources and inverter-based resources (IBRs) continue to dominate modern power systems, ensuring their transient stability during grid faults becomes increasingly critical. This webinar focuses on the dynamic behavior of phase-locked loop (PLL)-synchronized grid-connected inverters under low-voltage ride-through (LVRT) conditions. It provides a systematic overview of theoretical modeling, transient mechanism analysis, and control strategies to ensure inverter stability throughout the entire fault process—from pre-fault to post-fault recovery. The webinar highlights how PLL-synchronization dynamics, fault-clearing characteristics, inverter–grid and inter-inverter interactions jointly influence transient behavior. Advanced analytical methods combining the equal-area criterion and phase portraits are introduced to characterize different dynamic responses and reveal new instability phenomena, such as the emergence of unstable regions after fault recovery. The webinar further examines the influence of the practically used and crucial PLL frequency limiter (FL) on synchronization stability, clarifying its dual role in enhancing or degrading stability depending on system conditions. In addition, it extends the analysis to multi-inverter systems, demonstrating how inter-inverter interactions can pose both challenges and opportunities for transient stability, potentially inducing instability even when each inverter is individually stable, yet also enabling coordinated control to enhance overall system resilience.