Wind turbine and method for detecting low-frequency oscillations in an electrical supply grid

A wind power system for detecting low-frequency oscillations in an electrical supply grid having a line voltage and a rated line frequency, the wind power system comprising:

• a controller configured to:
• record a first series of measurements and a second series of measurements;
• perform a first frequency analysis on the first series of measurements for a lower frequency range and determine a first amplitude spectrum for the lower frequency range;
• perform a second frequency analysis on the second series of measurements for an upper frequency range and determine a second amplitude spectrum for the upper frequency range;
• determine whether the first amplitude spectrum has a first low-frequency oscillation component;
• determine whether the second amplitude spectrum has a second low-frequency oscillation component;
• and
• detect a presence of a low-frequency oscillation in response to at least one of:
• determining that the first amplitude spectrum has the first low-frequency oscillation component, and
• determining that the second amplitude spectrum has the second low-frequency oscillation component,
• wherein the low-frequency oscillation has a lower frequency than the rated line frequency, and
• wherein:
• the controller is configured to repeatedly run a first process loop, wherein the first process loop includes recording the first series of measurements, performing the first frequency analysis, determining the first amplitude spectrum, and determining whether the first amplitude spectrum has the first low-frequency oscillation component,
• the controller is configured to repeatedly run a second process loop, wherein the second process loop includes recording the second series of measurements, performing the second frequency analysis, determining the second amplitude spectrum, and determining whether the second amplitude spectrum has the second low-frequency oscillation component, and
• the first and the second process loops are matched such that the second process loop is run more frequently than the first process loop.