Synchronization Instability Analysis of Phase-Locked-Loop Interfaced Grid-Tied Inverter Under Abnormal Grid Conditions

Grid synchronization is essential for grid-tied inverters because it needs crucial information on the phase, frequency, and voltage amplitude of the grid. For grid-connected inverters (GCIs), phase-locked loop (PLL) is considered as an indispensable part of the control system to synchronize the inverters to the power grid. However, for abnormal grid operations, the PLL synchronized inverters typically exhibit low stability, phase error, frequency overshoot and frequency error problems which lead to synchronization instability of the inverters to the grid. Very few studies have addressed all the concerns and challenges regarding synchronization of GCIs, when the power grid suffers from various abnormalities like voltage sag/swell, phase jump, frequency jump and harmonic distorted phenomenon. In this study, the performance of widely used synchronous reference frame PLL (SRF-PLL) and dual second order generalized integrator PLL (DSOGI-PLL) considering various grid abnormal conditions is studied. This analysis clearly reveals the synchronization challenges, concerns, and research opportunities of designing robust PLL for power electronics dominated future grid, which will suffer from various abnormalities and instability issues. A three-phase LCL filter based GCI system is considered to investigate the performance of the PLLs under abnormal grid conditions.