Abstract: Doubly-fed wind turbine is easy to produce sub-synchronous oscillation in series compensation grid.

Using virtual synchronous control structure to improve inertia and damping for grid may also lead to subsynchronous oscillation risk. In view of the causes of sub-synchronous oscillation，firstly，the double-fed wind

turbine impedance model controlled by virtual synchronous machine was established in synchronous rotating

coordinate system，and the influence of series compensation and controller parameters on system stability was

analyzed by generalized Nyquist criterion，and compared and verified by time domain simulation results. Secondly，a voltage and additional damping cooperative compensation control strategy was proposed，and the stability before and after the additional control strategy was analyzed according to generalized Nyquist criterion，and the compensation control method was compared and verified by time domain simulation. The results show that the cooperative control strategy of voltage and additional damping cooperative compensation can effectively suppress sub-synchronous oscillation and improve the stability of grid-connected system.

      Key words: doubly-fed induction generator（DFIG）；series-compensated grid；virtual synchronous machine

control；sub-synchronous oscillation；voltage compensation；additional damping compensation control