A Hardware-in-the-Loop Approach to Enhanced Harmonic Suppression in Grid-Connected Inverters Using LCL Filters with Trap Branches

Harmonic suppression in grid-connected inverters is critical for maintaining power quality and ensuring the reliable operation of electrical systems. While traditional LCL filters are widely used for their superior harmonic attenuation capabilities, they often struggle with resonance issues. They are inadequate for suppressing higher-order harmonics under varying grid conditions. This paper presents a novel approach to enhancing harmonic suppression in grid-connected inverters through an optimized LCL filter design incorporating a trap branch. The proposed filter significantly reduces Total Harmonic Distortion (THD) and improves overall power quality by tuning the trap branch to the third harmonic. The effectiveness of the design is validated using a Hardware-in-the-Loop (HIL) simulation, which replicates real-world operating conditions with varying DC link voltages and current references. The results demonstrate a substantial THD reduction to 2.99% and the delivery of purely active power characterized by in-phase inverter current and grid voltage. This work advances the state of LCL filter design and offers a practical solution for improving power quality in modern renewable energy systems.