Improving Power Quality in Grid-Connected Photovoltaic Systems with FLL-Based Control for Nonlinear Demands

This study introduces and evaluates a 5 kW single-phase grid-connected photovoltaic (PV) system designed to operate effectively with nonlinear loads. Unlike conventional phase-locked loop (PLL) approaches, the system employs a second-order generalized integrator with a frequency-locked loop (SOGI-FLL) to improve power quality, support dynamic load management, and deliver accurate phase and frequency detection. The proposed control method utilizes FLL features to reduce harmonic distortion and ensure rapid adaptation to changing operating conditions. A voltage source converter (VSC) facilitates grid integration, ensuring robust synchronization and effective harmonic compensation. Comprehensive MATLAB/Simulink modeling and simulation were conducted across diverse solar irradiance profiles and nonlinear load scenarios. The results indicate that the source current consistently maintains a Total Harmonic Distortion (THD) level below 5%. This outcome not only confirms compliance with the IEEE 519 standard for harmonic control in power systems but also demonstrates the effectiveness of the proposed methodology in ensuring high-quality power delivery.