Low Voltage Ride-Through Capability of Grid-Connected PV Systems: A Comparative Study of Grid-Following and Grid-Forming Converters Under Current Limits

This study investigates the Low Voltage Ride-Through (LVRT) capabilities of grid-connected photovoltaic (PV) systems, focusing on the comparative performance of Grid-Following (GFL) and Grid-Forming (GFM) converters under current limit constraints. The two converters are designed to improve grid integration using systematic methodologies to ensure high performance and are compared under various grid fault conditions. A detailed model of the overall grid-connected PV system is first developed, including the PV array with its parameters extracted from the datasheet, Maximum Power Point Tracking (MPPT) algorithm, power converter topology, modulation technique, converter control structure (GFM or GFL) and the filter. The GFM converter employs a PQ droop control strategy. In contrast, the GFL converter utilizes conventional control techniques using a cascaded control structure along with the phase-locked loop (PLL) to synchronize the injected current with the grid voltage. The study evaluates the performance of both converters under several grid fault scenarios, considering current limit constraints imposed by the PV system and converter ratings. While GFM converters can enhance grid stability in weak grids due to their autonomous voltage and frequency regulation, the results demonstrate that GFL converters can exhibit superior performance under certain conditions, particularly when current limitations significantly impact the GFM converter’s response. Conversely, GFM converters demonstrate faster clearance times in specific scenarios, highlighting their potential advantages in dynamic stability. Using MATLAB/Simulink simulations, this research provides valuable insights into the impact of current limitations on the LVRT performance of both GFL and GFM converters across varying grid strengths, characterized by Short Circuit Ratio (SCR) and Grid Impedance Ratio (GIR), enabling the selection of the most suitable converter topology for specific grid conditions.