Electromechanical Oscillation Analysis and Suppression of Grid Forming DFIG-Based Wind Turbines Under Weak Grid

The current research indicates that the implementation of grid-forming (GFM) control in doubly-fed induction generator (DFIG) wind turbines (WTs) has the potential to enhance the stability of electrical systems in weak grids. However, there is a scarcity of studies on the electromechanical stability of DFIG under GFM control. The investigation begins with formulating a small-signal model for the electromechanical system of a GFM DFIG connected to a weak grid. The theoretical analysis reveals that, as the grid strength diminishes, the system becomes susceptible to electromechanical oscillations near the natural frequency (NF) of the drivetrain. Subsequently, the paper scrutinizes the drivetrain damping branch within the control system, establishes an average energy dissipation model during the drivetrain NF oscillation period, and examines the mechanisms causing drivetrain oscillations (DOs). Additionally, optimization recommendations for oscillations are presented from the perspective of GFM control parameters. Nevertheless, achieving a balance between drivetrain stability and electrical stability remains challenging, especially in extremely weak grids. Therefore, the paper proposes a hybrid <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d-q</i> axis voltage reference drivetrain damping control (HVRDC) tailored for GFM control. Theoretical analysis demonstrates that, even in the presence of an extremely weak grid, the proposed strategy ensures the stability of the GFM DFIG-based WT. Finally, the accuracy of the theoretical analysis is substantiated through a control-hardware-in-loop (CHIL) experiment.