This paper proposes a control scheme which allows doubly fed induction wind generators (DFIWG) to participate effectively in system frequency regulation. In this control approach, wind generators operate according to a de-loaded optimum power extraction curve such that the active power provided by each wind turbine increases or decreases during a system frequency changes. The control strategy defined at the wind generator to supply primary frequency regulation capability exploits a combination of control of the static converters and pitch control, adjusting the rotor speed and the active power according to the de-loaded optimum power extraction curve. Results obtained in a small isolated system are presented to demonstrate the effectiveness of the approach.Index Terms -Primary frequency control, dynamic behavior, wind generation. J. A. Peças Lopes is with INESC Porto and Faculdade de Engenharia da Universidade do Porto (FEUP), Rua Roberto Frias 378, 4200-465 Porto,

This paper proposes an optimized dispatch control strategy for active and reactive powers delivered by a doubly fed induction generator in a wind park. In this control approach, wind turbines are supposed to operate over a deloaded maximum power extraction curve and will respond to a supervisory wind farm control after a request from a system operator for adjusting the outputs of the wind park. The definition of the active and reactive powers operating points, for each wind turbine, is defined from an optimization algorithm that uses the primal-dual predictor corrector interior point method. The control strategy used at the wind generator level exploits a combination of pitch control and control of the static converters to adjust the rotor speed for the required operation points. A small wind park is used to illustrate the effectiveness of the developed approach.Index Terms-Active and reactive power dispatch, control systems, nonlinear programming, optimization strategies, wind generators.

This work demonstrates that the integration of variable-speed wind systems with doubly fed induction generators (DFIGs) and a four-quadrant ac-to-ac converter connected to the rotor windings increases the transient stability margin of the electrical grids, when compared with the case where the fixed speed wind systems with cage generators are used. It is due to the influence of the two dedicated rotor current regulators of the DFIG on the dynamic behavior of the other generators in the system. Besides, adequate models to represent the behavior of the DFIG in transient stability studies are presented. From the simulation results, some important conclusions can be extracted to guide the integration of the wind farms on weak or strong grids.Index Terms-Decoupled control, doubly fed induction generator (DFIG) protection, electrical grids, fixed speed wind systems, transient stability margin, variable-speed wind systems.

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