Transient stability analysis of grid connected wind turbines employing induction generators

Abstract

The number of grid connected wind turbines has been recently in a continuous growth. Therefore, it becomes extremely essential to analyze the transient stability of power systems with these new units. In this thesis, the transient stability of fixed speed wind turbines is investigated. A power flow algorithm is established to provide the necessary initial conditions for the dynamic simulation. The transient machine models are presented further together with their comprehensive initialization and integration techniques. These comprise the synchronous machine two-axis model, the AVR excitation system model, and the wind turbine electrical and mechanical system models. The validity of the proposed models is verified by a transient stability program that is developed in MATLAB and used to perform a case study on the 220-150 KV Lebanese network with a wind farm. In this study a three phase fault is simulated and the machine angles along with the turbine speeds are noted. Simulations show that a one mass model doesn’t adequately represent the oscillatory response of a windmill in contrast to a two mass model. The former yields optimistic results in terms of the critical clearing time, which in turn is affected by the reactive power consumption, the fault location, the penetration level and the machine parameters.