Input Admittance Modeling and Stability Analysis of DFIG Under Weak Grid Condition

The interaction between the double fed induction generator (DFIG) control system and the grid has been paid great attention in weak grid connection condition. Traditional DFIG converter control system is normally designed without considering the impact of grid impedance. The impedance-based method is used to analyze the relationship between the converter control system and the stability of DFIG grid connected system. The model of DFIG equivalent input admittance in synchronous frame with PLL dynamics considered is given for the first time. The electromagnetic transients of DFIG and current controller are also included in the input admittance model. Specific analysis is presented on how controller parameter variations affect the input admittance matrix. By applying the Generalized Nyqusit Stability Criterion(GNC), stability of the DFIG system connected to weak grid can be predicted with the proposed input admittance model. Impact of the current loop and PLL proportional and integral parameters on system stability is discussed and demonstrated with the Nyquist map. Simulation results verify the validity of the proposed input admittance model and theoretical analysis.