Systematic Design and Performance Evaluation of LCL-Filtered Grid-Forming Inverters under Different Operating Conditions

Abstract

This study aims to develop a systematic design for inductor-capacitor-inductor (LCL)-filtered grid-forming inverters (GFMIs) and evaluates their performance under various operating scenarios. The proposed methodology presents the mathematical modeling of GFMI in the dq reference frame, designs the LCL filter parameters within a stable resonance-frequency region, and employs a bandwidth-coordination scheme to design cascaded current and voltage controllers. Small-signal stability analysis based on eigenvalues is used to assess stability under varying grid strength and parameter variations. Results from MATLAB/Simulink show that the proposed design provides stable operation and acceptable dynamic performance in both grid-connected and stand-alone modes. Furthermore, the inverter output voltage and current achieve low total harmonic distortion (THD) of 4.3% and 1.2%, respectively, at rated load. Although current THD increases under light-load grid-connected mode, the total demand distortion (TDD) remains below 5% for all tested conditions, thereby satisfying the requirements of IEEE Standard 519.