A Generic Voltage Control for Grid-Forming Converters With Improved Power Loop Dynamics

Abstract

Grid-forming converters (GFMCs) provide voltage support and other grid services, such as inertia and droop, in more-electronics power systems. The GFMCs with small droop coefficients or connected to the grid through a small impedance may have a fast power loop, which leads to serious conflicts with the inner ac voltage control loop, resulting in power oscillations or even instability. To address this problem, an extremely fast ac voltage loop should be expected for GFMCs. On top of that, GFMCs must operate well in both stand-alone and grid-tied conditions. Through detailed analysis, this article first reveals that the grid-tied operation of a dual-loop controlled GFMC with an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> output filter features a much slower voltage control loop than that of the stand-alone mode. To improve the dynamics of GFMCs, we propose a generic voltage control scheme with a high-pass filter in the current feedback loop. The generic voltage controller has fast voltage tracking performances under both grid-tied and stand-alone operations, thereby enabling GFMCs to achieve better power regulation and grid service. The improvements in both voltage tracking and power control are verified via experiments.