Comparison and evaluation of induction generator models in wind turbine systems for transient stability of power system

In order to analyze the transient stability of grid-connected squirrel cage induction generators (SCIG) in wind power generating systems, various mathematical models, including the detailed and reduced generator models as well as the one-mass and two-mass shaft system models, are studied in this paper. Based on the different wind turbine system models, the dynamic behaviors are simulated and compared by using Matlab/Simulink, under the condition that the generator stator terminal is subjected to a three-phase short-circuit fault. In addition, the critical clearing time (CCT) is calculated and compared by using a direct method with critical clearing slip of induction generators and a method of trial and error by simulation, for different system models at the various operation conditions. The models and methods suitable to analyze the transient stability of the wind turbine systems based on SCIG are discussed in detail. Several comparative results have shown that the valid transient stability model of SCIG in wind turbine systems has to incorporate the two-mass shaft system model, the direct method of CCT estimation based on critical clearing slip is incompatible to determine the transient stability limit, owing to the large multi-oscillation of the generator rotor speed during the fault period.