  Rising wind energy integration, accompanied by a decreasing level of system
inertia, requires additional sources of ancillary services. Wind turbines based
on doubly fed induction generators (DFIG) can provide inertial and primary
frequency support, when equipped with specific controls. This paper
investigates the effect of frequency support provision by DFIGs on the
small-signal stability of power systems. To this end, a modified version of the
Kundur two-area test system is employed to analyze different scenarios. Wind
energy generation is either added to the existing system or displaces part of
the synchronous generation. Simulations show that primary frequency support
tends to improve the damping of electromechanical oscillations and deteriorate
it for converter control-based ones. On the other hand, inertial response may
be either beneficial, detrimental or negligible to damping, depending on the
tuning of control parameters.
