A Modified Current Reference Generation Method for Minimizing Active Power Oscillations During Asymmetrical Low-Voltage Ride-Through (ALVRT) in Grid-Tied PV-Fuel Cell Systems

In recent updates to grid codes, various regulations for multiple countries have been updated to improve the reliability and robustness of power systems. One of these regulations is Low Voltage Ride-Through (LVRT), which states that photovoltaic (PV) systems must maintain continuous connection to the utility grid in the event of voltage sags at the Point of Common Coupling (PCC). This work is dedicated to the injected power oscillations at the PCC location, especially for asymmetrical voltage sag conditions, where the presence of negative sequence components gives rise to oscillations at twice the grid frequency. A modified reference generation strategy of currents based on the synchronous reference frame is developed to reduce these effects. Using the newly defined factor to realize the voltage unbalance factor (VUF) along with the gain parameter <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$m$</tex>, the proposed method is found to significantly reduce oscillations. It reduces the overall content of imbalance in the system and prevents overvoltage in healthy phases while reducing power oscillations. Additionally, the gain factor helps to limit the ripples of the DC link voltage, thus contributing to improving the lifespan of the capacitor. This study is consistent with the requirements of the Indian grid code, considering the standards for reactive current injection. The proposed control scheme is tested with the help of MATLAB/Simulink simulations.