Method of operating a DFIG wind turbine under SSR

A method of protecting a wind turbine with a doubly-fed induction generator (DFIG) against a sub-synchronous resonance (SSR) event, the method comprising:

• measuring a plurality of output values of an output parameter of the wind turbine during a first measurement cycle;
• monitoring an oscillation parameter obtained using the plurality of output values, wherein the oscillation parameter is a counter value of output values that exceed a limit during a single measurement cycle;
• determining, based on comparing the oscillation parameter with a first threshold, whether the plurality of output values indicates a SSR event critical for further operation of the wind turbine;
• and
• shutting down the wind turbine when the oscillation parameter exceeds the first threshold for one or more measurement cycles.

A wind turbine controller of a wind turbine with a doubly-fed induction generator (DFIG), the wind turbine controller being arranged to protect the wind turbine against a sub-synchronous resonance (SSR) event, the wind turbine controller configured to perform an operation comprising:

• receiving a plurality of output values of an output parameter of the wind turbine during a first measurement cycle;
• monitoring an oscillation parameter obtained using the plurality of output values, wherein the oscillation parameter is based on a deviation value calculated based on an integration of differences between the output values and a reference output value, wherein the deviation value is stored when the deviation value exceeds a deviation threshold;
• determining, based on comparing the oscillation parameter with a first threshold, whether the plurality of output values indicates a SSR event critical for further operation of the wind turbine;
• and
• shutting down the wind turbine when the oscillation parameter exceeds the first threshold for one or more measurement cycles.