An improved virtual inductance control method considering PLL dynamic based on impedance modeling of DFIG under weak grid

Impedance-based method is an effective method to analyze the system stability. Based on the impedance stability theory, an improved virtual inductance control method considering PLL dynamic is presented for the stability of doubly-fed induction generator (DFIG) under weak grid condition. Firstly, equivalent input admittance model of the DFIG system including all its controller is developed in the synchronous reference (d-q) frame. Secondly, the generalized Nyquist criterion (GNC) proves that the stability of the DFIG system can be improved by increasing the rotor inductance. Then, a virtual inductance term is introduced into the RSC current controller to emulate additional inductance in the rotor. However, the virtual inductance method may be ineffectual due to the influence of the PLL dynamic under weak grid condition. Therefore, an improved virtual inductance control method considering the PLL dynamic is implemented to improve the stability of the DFIG system under weak grid condition, and the simulation is used to verify the effectiveness of the improved virtual inductance control strategy.