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In this article, stabilization methods of wind farms composed of fixed-speed wind turbines and variable-speed wind turbines are analyzed. A current-controlled voltage source converter scheme for a variable-speed wind turbine driving doubly fed induction generator is proposed. The proposed scheme is then compared with two other doubly fed induction generator control schemes to show the effectiveness of the proposed controller. Different types of symmetrical and unsymmetrical faults are analyzed considering wind farm recent grid codes. Though all of the schemes are able to stabilize the wind farms during transient conditions, the proposed current-controlled voltage source converter scheme offers the advantage of less intricacy of controller design, better performance during grid fault, and omission of DC-link protection scheme, which can reduce the overall cost of the system. Moreover, extensive simulation analyses by using PSCAD/EMTDC (Manitoba HVDC Research Center, Manitoba, Canada) are performed to determine the optimum amount of the fixed-speed wind turbine system that can be stabilized by variable-speed wind turbine system. [ABSTRACT FROM PUBLISHER]

In this article, the blade and shaft torsional oscillations of wind turbine generator system (WTGS) when a network disturbance occurs in the power system are analyzed. Several reports are available in the literature, where the damping of shaft torsional oscillations of steam turbine generator system is discussed. Though a huge number of wind generators are going to be connected with the existing network, the damping of blade-shaft torsional oscillations of WTGS has so far not been reported. In this work, for the damping of blade-shaft torsional oscillations of WTGS, the voltage source converter (VSC) based three-level STATCOM is proposed. The six-mass drive train model of WTGS is used for the sake of precise analysis. Moreover, the damping of blade-shaft torsional oscillations of WTGS by using pitch controller is analyzed also, since a pitch controller is attached with most of the recent wind turbines. Both symmetrical and unsymmetrical faults are considered as the network disturbances. Simulation results clearly show that the pitch controller can somewhat, and the STATCOM can significantly, decrease the blade and shaft torsional oscillations of WTGS, where the simulations have been done by PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

In order to investigate the impacts of the integration of wind farms into utilities networks, it is necessary to analyze the transient characteristic of wind turbine generator system (WTGS). In most of the cases, the simple one mass lumped model is considered for stability analysis of wind generator. It is not analyzed yet which order shaft model is sufficient for transient stability analysis of WTGS. In this study, a detailed transient analysis has been done with the consideration of two mass and three mass shaft models of WTGS. Finally, it is concluded that two mass shaft model is sufficient enough for transient stability analysis of grid connected WTGS. [ABSTRACT FROM AUTHOR]