Stability Analysis and Harmonic Filtering Enhancement of Single-Voltage-Loop PI- Controlled Grid-Forming Converters

Grid-forming converters (GFMCs) remain on a strong growth trajectory in the field of power electronics due to ac voltage formation and frequency regulation capabilities. Compared with multiloop control strategies, single-loop voltage control benefits from the simplicity of sensors and controllers, rapid dynamics, and no voltage/current control interaction. However, as revealed by this article, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i>-filtered GFMCs with single-voltage-loop proportional–integral (PI) controllers feature a high resonance frequency for stable operation in grid-tied and islanded scenarios, which deteriorates switching harmonic filtering due to the small filter size. As such, we propose a switching harmonic filtering enhancement strategy for GFMCs by the use of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLCL</i> filter, whose <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> trap forms a serial resonance at the switching frequency and, thus, allows improved harmonic attenuation. In this way, we achieve strong switching harmonic filtering of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLCL</i>-filtered single-voltage-loop PI-controlled GFMCs. Furthermore, this article derives relevant stability regions. Finally, simulation and experimental results verify the theoretical analysis and switching harmonic attenuation capability.