short circuit ratio(SCR)

The converter controller of wind turbine presents capacitive impedance characteristics with negative resistance at subsynchronous frequencies. When it is connected to weak AC power grid, it will form an LC resonant circuit with system-side inductance, and generate sub-/super-synchronous oscillations due to negative damping effect. A PSCAD simulation model of direct-drive wind farm connected to AC power grid is provided to study the above phenomenon.