I found this answer for your question

from Dr. pisupati sadasive subramanyam

Reactive Power(leading0 can be generated by over excited synchronous motor running on no load or light load.Then it is known as Synchronous Condensr

When two alternators are connected in parallel,changing the excitation of one alternator changes the power factor of both the machines causing exchange of reactive power between the two machines(Refer parallel operation of two alternators).

http://www.labvolt.com/downloads/download/86376_F0.pdf

Doubly Fed Induction Motor: A three-phase wound-rotor induction machine can be set up as a doubly-fed induction motor. In this case, the machine operates like a synchronous motor whose synchronous speed (i.e., the speed at which the motor shaft rotates) can be varied by adjusting the frequency of the rotor ac currents fed into the rotor windings. The same wound-rotor induction machine setup can also serve as a doubly-fed induction generator. In this case, mechanical power at the machine shaft is converted into electrical power supplied to the ac power network via both the stator and rotor windings. Furthermore, the machine operates like a synchronous generator whose synchronous speed (i.e., the speed at which the generator shaft must rotate to generate power at the ac power network frequency can be varied by adjusting the frequency of the ac currents fed into the rotor windings.

When operating as Synchronous Motor, as there is no separate D.C. Field Excitation,it cannot be run as Synchronous Condenser.

Doubly-fed induction generators come into play, as they allow the generator output voltage and frequency to be maintained at constant values, no matter the generator rotor speed (and thus, no matter the wind speed). As seen in the previous section, this is achieved by feeding ac currents of variable frequency and amplitude into the generator rotor windings. By adjusting the amplitude and frequency of the ac currents fed into the generator rotor windings, it is possible to keep the amplitude and frequency of the voltages (at stator) produced by the generator constant, despite variations in the wind turbine rotor speed (and, consequently, in the generator rotation speed) caused by fluctuations in wind speed. By doing so, this also allows operation without sudden torque variations at the wind turbine rotor, thereby decreasing the stress imposed on the mechanical components of the wind turbine and smoothing variations in the amount of electrical power produced by the generator.

Using the same means, it is also possible to adjust the amount of reactive power exchanged between the generator and the ac power network. This allows the power factor of the system to be controlled (e.g., in order to maintain the power factor at unity).

P.S.

thank you very much for your accurate answer.