This paper presents how wind farms, adequately controlled, can improve the stability properties of a power system. Considerations of modeling of wind farms are presented. Then, the wind farm control laws under normal conditions are presented. Next, other wind farm control laws are added to the first ones looking for damping the system electromechanical oscillations after a network disturbance. These laws are based in the capability of the double fed induction generators of feeding active and reactive powers. Finally, some simulations are shown to support the theoretical considerations