The low-frequency instability in variable speed constant frequency doubly fed induction generator(DFIG)widely used in wind power generation is investigated. The low-frequency oscillation phenomena in DFIG are analyzed via numerical simulation as the input mechanical torque increases. The simulation results show that the low-frequency oscillation enhances total harmonic distortion(THD)of stator current

thus decreases the system performance. Then a mathematical model of the closed-loop system is derived. The Jacobian eigenvalue analysis shows that the low-frequency oscillation is essentially caused by the Hopf bifurcation

thus the stability boundaries are given according to this analysis. This study is helpful to better understand nonlinear dynamics of DFIG

and is valuable to parameter design for guaranteeing stable operation of this system.