Novel VSG Control to Enhance DFIG Oscillatory Stability in Weak Grids via Admittance Modeling: Analysis and Experimental Validation

Doubly-fed induction generators (DFIGs) often display negative resistance characteristics at low frequencies when using traditional grid-following control, which can lead to oscillation issues in weak grids. To address these challenges, this paper proposes a virtual synchronous generator (VSG) control method-a grid-forming control strategy-that enhances phase and frequency stability of power systems, even under off-grid conditions. However, existing small-signal models of VSG-DFIG systems fail to account for frequency coupling effects, which can result in inaccurate assessments of system stability. To address this deficiency, this paper develops a Multi-Input Multi-Output (MIMO) frequency-coupled admittance model for the VSG-DFIG system, which accounts for VSG control, cascaded inner control loops, and control delay effects. Through this model, we systematically analyze the impact of various parameters on frequency coupling and system stability within weak grids. Building on these analytical insights, a novel VSG control method is introduced to ensure the stability of the DFIG system. Experimental results validate the theoretical analysis and demonstrate the effectiveness of the proposed control strategy.