A DFIG Impedance Reshaping Method Based on Offsetting Rotor Current Dynamic to Solve the Instability Issue Caused by PLL

The grid-following control strategy based on phase-locked loops (PLL) is widely used in doubly-fed induction generator (DFIG) systems. However, the PLL will lead to frequency coupling as well as negative resistance characteristics, which may worsen the stability of the DFIG grid-connected system and even lead to oscillation risk in low frequency, especially in weak grid conditions. According to the eigen-loci of the DFIG interconnected system considering different simplified conditions, this paper revealed the impact of different PLL-related matrices and presented a DFIG stability-enhanced method through offsetting the dynamic of rotor current to solve the instability issue related to PLL. Meanwhile, the effectiveness of the stability-enhanced method is verified by simulation based on the Matlab/Simulink platform.