Studies Of Transient Stability For Grid-Connected Wind Turbine With Induction Generator

Due to the increasingly tense energy and the incremental rate of environmental concern, wind power generation technologies have been widely applied all over the world. With large-scale wind farms in the planning and construction, the penetration of wind power in electrical power systems gradually increase, the influence of wind power to the power systems raise. Therefore, deeply studying the transient behavior of power systems with high penetration level of wind power, especially in the transient stability of wind power generator system including transient stability mechanism, modeling and transient stability assessing method, has become a hot issue in domestic and international research field.This thesis mainly focuses on gird-connected wind turbine with squirrel cage induction generator. Firstly, based on comparatively analyzing the transient stability difference between asynchronous generator and synchronous generator, the transient stability mechanism of grid-connected wind turbine with induction generator is studied. Secondly, based on combinations of the generator models and turbine shaft models, the transient behaviors of wind turbine system by using different models are investigated, under the condition of mechanical disturbance and electrical disturbance. Then the more suitable models for transient stability analysis of grid-connected wind turbine with induction generators are obtained. Based on the suitable model, the influences of wind turbine parameters to the transient stability of wind turbine system are studied. And a three mass wind turbine equivalent model considering both blade and shaft flexibility is firstly proposed to study the influence of wind turbine blade stiffness. Again, Based on analyzing the existing control strategies, a new pitch control strategy considering shaft flexibility is proposed to improve the transient stability of wind turbine system. The effects of these control strategies are compared and these strategies also mixed to enhance the transient stability. Lastly, based on the transient stability assessment of the conventional power system, a Normal Form method based on the theory of stability boundary for nonlinear dynamic system are introduced to assess the transient stability of grid-connected wind turbine with squirrel cage induction generator, a model of critical clearing time calculation based on normal form theory is developed. And the calculation results were also comparatively analyzedThe conclusions obtained in this thesis, including transient models of gird-connected wind turbine with induction generator, measures to enhance the transient stability of wind turbine system, and transient stability accessing method, will provide theory basis and decision support for transient stability analysis of power systems with large-scale wind farms.