Accurate Modeling and Stability Enhancement Methods for Grid-Following and Grid-Forming Hybrid-Controlled Converters

Abstract

With the widespread application of renewable energy grid-connected technologies in power system, grid-connected converters are increasingly challenged by more complex operating conditions. A particularly notable issue is that the short circuit ratio (SCR) of grid significantly affects the stability of grid-connected converters, and the SCR may vary over a wide range. Consequently, grid-connected converters are required to exhibit strong adaptability when the SCR changes. Therefore, based on a grid-following/grid-forming hybrid control strategy which has been proven to inherently possess strong adaptability to SCR variations, this paper first fills the gap in the mechanistic analysis of this hybrid control strategy. Through accurate modeling, both the couplings among control variables and the interactions between internal control loops and external grid conditions are precisely described. Furthermore, an adaptive adjustment strategy for the weight coefficient of grid-following and grid-forming hybrid control is proposed. This strategy effectively ensures stable grid connection of the converter under wide range SCR variations and improves its phase margin, which increases the robustness of hybrid-controlled converter. Finally, simulation and experimental results validate the effectiveness of the proposed strategy.