Strategy for Suppressing Shaft System Oscillations in Grid-Forming Doubly-Fed Wind Turbine Under Weak Grid Conditions

As the penetration rate of wind power continues to increase, the weak grid characteristics at wind power grid connection points become more apparent. Grid forming doubly-fed wind turbine systems, based on power synchronization, have attracted widespread attention due to their good performance in weak grid environments. In terms of stability, the coupling relationship between reactive power control and active power/speed loops in weak grid conditions can make the system output power susceptible to the inherent oscillation characteristics of the drivetrain structure, leading to the occurrence of low-frequency oscillations. To address this issue, this paper first establishes a small-signal model of the power loop and speed loop for the grid-forming doubly-fed wind turbine, and analyzes the coupling relationship between reactive power, active power, and speed response. Then, based on the small-signal variation relationship between active power and reactive power, the method of adding damping to the drivetrain is employed to suppress the amplification effect of the drivetrain on shaft system oscillation characteristics. The electrical damping analysis method demonstrates that this strategy can effectively reduce the risk of low-frequency oscillations in grid-connected doubly-fed wind turbine systems. Finally, the effectiveness of this strategy is verified through Simulink simulations.