A PSCAD simulation model of direct-drive wind farm connected to the grid via VSC-HVDC is provided. Because there are a large number of power electronic devices and complex multi-time scale control links in the system, there is mutual coupling between power electronic devices or between power electronic devices and the power grid, which may lead to the risk of oscillation in the wide-band range from several hertz to hundreds of hertz.



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.



A typical model of doubly-fed wind farm connected to the grid through series compensation is provided, which can be used to study subsynchronous oscillation(SSO). LC resonance may occur between the stator inductance and the capacitance in the 500kV line. At some frequencies, the equivalent resistance of the rotor is negative, and the proportional factor of the inner current loop of the rotor-side converter(RSC) will amplify the negative resistance, resulting in unstable subsynchronous control interaction(SSCI) in the system.