Abstract

The rapid integration of inverter-based renewable energy sources has significantly altered the dynamic behaviourofmodern power systems, particularly under low-inertia and weak grid conditions. Conventional grid-following invertersrelyonphase-locked loop–based synchronisation and are inherently dependent on the presence of a strong grid, which limits theirabilityto operate during grid outage events. In contrast, grid-forming inverters are capable of autonomously establishingvoltageandfrequency, enabling stable islanded operation when supported by battery energy storage systems. This paper presents a comparative investigation of grid-forming and grid-following control strategies for a solar photovoltaicsystem integrated with battery energy storage under grid outage conditions. A detailed simulation model is developedusinganidentical system configuration for both control approaches, ensuring a fair and consistent comparison. The analysis focusesonvoltage and frequency regulation, active and reactive power behaviour, and harmonic performance during the transitionfromgrid-connected to islanded operation. Simulation results demonstrate that the grid-following system experiences loss of synchronisation and degraded powerqualityfollowing grid disconnection, whereas the grid-forming system maintains stable voltage and frequency with seamless islandedoperation. Furthermore, the grid-forming control exhibits reduced voltage and current total harmonic distortion comparedtothegrid-following approach. These findings highlight the effectiveness of battery-supported grid-forming control in enhancingsystemstability and power quality during grid outage events in renewable-dominated power systems.