Mitigating harmonics and voltage disturbances in PV systems through intelligent multi-level inverter modulation and active filtering under grid disturbances

Abstract

High-penetration photovoltaic (PV) plants integrated into weak or distorted grids suffer from power quality degradation. Voltage sag/swell, unbalance, and background harmonics may exacerbate inverter distortion and lead to unintended tripping. In this paper, a novel approach for harmonic and voltage distortion mitigation in grid-connected PV systems is presented. The methodology combines intelligent multi-level inverter modulation with coordinated shunt active power filtering. A disturbance-aware modulation layer dynamically modulates switching states to nullify dominant harmonic clusters, and a joint active filter extracts and compensates harmonic/reactive components with minimal interference in DC-link regulation. A supervisory disturbance classifier with waveform features, such as sag depth and negative sequence content, adapts control weights and filter gains online. Some case studies on simulation and hardware-in-the-loop simulate balanced operation, sag and swell events, unbalanced faults, and harmonics-polluted grids. Under disturbed conditions, the proposed scheme reduces THD for grid current from around 5–8% to less than 2%, complying with IEEE 519, while tracking a near-unity power factor and maintaining stable DC-link voltage. The voltage sag has an approximately 30–50% reduction in voltage deviation envelopes from fixed-modulation baselines, and recovery occurs within just a few oscillations depending on the disturbance level. Correlated smart multi-level modulation, together with adaptive active filtering, enhances disturbance ride-through capability and harmonic behavior under weak-grid conditions. The approach offers an applicable way to interconnect PV-based sources with better power quality support and less resonance sensitivity in cases of changing grid impedance.