The phase locked loop(PLL)used in doubly fed induction generator(DFIG)system can cause frequency coupling phenomena and give negative resistance characteristics in low frequency,which leads to instability issues,especially in weak grid conditions.Firstly,the multi-input multi-output(MIMO)impedance model for DFIG system is established.And then,based on the generalized Nyquist curves of DFIG interconnected system with different simplified conditions,the influence of different PLL-related matrices is revealed,and a low freqnency oscillation suppression strategy based on rotor current compensation is proposed,which can greatly reduce the frequency coupling and negative resistance characteristics introduced by PLL,thus improving the grid-connected stability of DFIG under weak grid conditions.Finally,an electromagnetic transient model of DFIG grid-connected system is established in Matlab/Simulink,and the simulation results verify the correctness of theoretical analysis and the effectiveness of the proposed method.
doubly fed induction generatorphase locked loopsmall signal stabilityoscillation suppression
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