The growing integration of renewable energy sources (RESs), especially solar photovoltaic (PV) systems, has intensified the demand for high-quality and stable grid connections. This study reviewed shunt active power filter (SAPF) configurations and multilevel converters (MLCs), with a focus on improving power quality, scalability, and fault diagnostics in large-scale PV and battery energy storage systems (BESS) applications. A comprehensive methodology was employed to review and analyze multilevel SAPF topologies, inverter control strategies, modulation techniques, and hybrid semiconductor devices. The research discussed integration challenges, including current harmonics, voltage instability, and fault localization in MLCs using model-based and data-driven strategies. Review findings highlight the superior performance of five-level MLC-based SAPFs in reducing harmonic distortion, improving waveform quality, and enhancing control flexibility. Additionally, hybrid Si/SiC switch strategies and advanced modulation techniques like LS-PWM and predictive control demonstrate improved efficiency and fault tolerance in grid-connected applications. The study recommends further development of intelligent control schemes, modular SAPF design, and integration with energy storage for robust and adaptive grid systems. Advancements in semiconductor technologies and AI-based diagnostics are key to future reliability and performance enhancements.

The increasing integration of photovoltaic (PV) systems and nonlinear loads intensifies harmonic distortion and reactive power imbalance in modern power networks. Conventional shunt active power filters (SAPFs) often employ control strategies that perform poorly under uncertain and dynamic grid conditions. This paper develops a hybrid sliding mode control with disturbance observer (SMC+DOB) technique for a PV-integrated SAPF to achieve effective harmonic mitigation, reactive power compensation, and enhanced system robustness. The study models the PV-SAPF system in MATLAB/Simulink (R2025b), where the SMC ensures robust current tracking, while the DOB estimates and suppresses unknown disturbances in real-time. The controller’s performance is evaluated under varying nonlinear and reactive load conditions, as per IEEE 519-2014 standards. Simulation results show that the proposed SMC+DOB scheme reduces total harmonic distortion (THD) by 96.7%—from 31.45% to 1.05%—while maintaining DC-link voltage stability and unity power factor. The integrated control architecture enhances the dynamic performance of SAPF, providing superior harmonic suppression, fast transient recovery, and improved grid stability for PV-connected systems.