In this paper, the unified admittance model of the DFIGincluding RSC and GSC is established in the dq coordinatesystem and also a method of introducing additional dampingcontrollers in the DFIG’s RSC and GSC to suppress SSO isstudied. Now the main conclusions are as follows:1) A unified admittance model for the DFIG is established.The model considers the effects of rotor side controller’s innercurrent loop, outer power loop, grid side controller’s innercurrent loop, outer DC voltage loop and phase locked loopdynamics.2) According to the GNC, the main influencing factors ofthe SSO of the DFIG’s series compensation system areanalyzed. It is proved that the additional damping controllercan improve system stability, and the change of the admittancecharacteristics of the DFIG after the introduction of theadditional damping controller is analyzed by Bode diagram.3) The additional damping control signal of RSC is selectedas the stator current disturbance amount, and the GSC’s isselected as the GSC current disturbance amount, which fullyconsiders converter’s own control characteristics. When theparameter selection is reasonable, the mutual influencebetween the RSC and the GSC additional damping control issmall.