Stability Analysis for DFIG-Based Wind Farm Grid-Connected System Under All Wind Speed Conditions

The stable operation capability of the doubly-fed induction generation-based wind farm grid-connected system (DFIG-WFGS) is closely related to wind speed, and the windward velocity of wind turbine unit at different locations may be discrepant due to wake effect. However, the existing mathematical models of DFIG is limited to some specific wind speed points, which may not be directly applied to stability analysis in all wind speed operating conditions. The wind speed is used to characterize the steady state operating point in this paper, meanwhile considering the wake effect and single-input and dual-output (SIDO) characteristics, the two-variable admittance models of wind farm based on DFIG are proposed. Further, the improved analysis method based on two-variable open-loop transfer function is proposed to investigate the stable wind speed interval with different series compensation level for a 50MW DFIG-WFGS in Qinghai, China. In addition, a design guideline of wind farm for oscillation suppression is studied to enhance the performance of DFIG-WFGS and avoid unstable operations. Theoretical analysis and simulation results show that the wake effect may discontinuous the stable wind speed interval, and the damping variation is not positively correlated with the wind speed, which provides basis for accurate analysis and effective improvement of the stability for wind power generation system.