Analyzing R/X Stability Regions of Parallel Grid-Connected Inverters Using Hardware-in-the-Loop Approach

This paper investigates the critical issue of ensuring stable operation in grid-connected inverters and inverter-based distribution grids, focusing on the influence of variable $R / X$ ratios and parallel connections of inverters on system stability in weak grids. Utilizing the power-hardware-in-the-loop methodology, an experimental setup is designed for authentic assessments of grid-connected inverters under diverse conditions. This setup includes an RTDS real-time simulator, a Ponovo 4-quadrant amplifier, a real 4 kW inverter, and a modeled grid with simulated inverters, connected in parallel with the real inverter. The results include experimentally obtained stability regions considering grid R and L parameters. Notably, findings indicate an expanded stability region with parallel inverters, enabling operation with lower $R / X$ ratios. This research contributes to understanding inverter stability at a distribution level of 0.4 kV. The insights gained are crucial for improving grid-connected inverter performance and streamlining the integration of renewable energy sources, thereby advancing the reliability and sustainability of power systems.