Transient Stability Analysis of Grid-Connected Induction Generators Using Normal Form Method

This paper explores the possibility of using normal form method for transient stability analysis of grid-connected squirrel cage induction generators (SCIG) considering with rotor electrical transients. The theory of nonlinear dynamic system for power system stability boundary approximation is introduced briefly. The third-order state equations of SCIG equivalent to a synchronous generator with the voltage adjustment mechanism are studied. In order to quickly obtain the trajectory on fault in linear system subspace (z subspace), a nonlinear normal form inverse transformation is derived. A method of critical clearing time (CCT) calculation based on normal form theory is developed, which is applied to the proposed SCIG system dynamic models. Under the condition that the generator stator terminal is subjected to a three-phase short-circuit fault, the CCT at the various initial mechanical torques are calculated by using the normal formal method, and compared with a trial and error method by simulation. Several results have shown that the proposed model and method for transient stability analysis of SCIG are valid