An Improved PLL Control Method for DFIG Under Asymmetric Faults

With the continuous expansion of new energy sources, the issue of system instability caused by the large-scale integration of wind power into weak grids has become increasingly prominent. To address this challenge, this paper first develops a sequential impedance model for the doubly fed induction generator (DFIG) grid-connected system with a single-input-single-output (SISO) framework. Building upon this model, the critical role of phase-locked loop (PLL) performance in system stability is analyzed, highlighting that voltage disturbance components can significantly impair PLL performance and potentially lead to system instability. Subsequently, a voltage disturbance separation compensation (VDSC) control strategy based on an improved second-order generalized integrator frequency-locked loop (ISOGI-FLL) is proposed. Nyquist stability analysis and simulation results demonstrate that the proposed control strategy effectively enhances PLL performance and improves overall system stability.