Comparison of methods for estimating short-term damping of idling wind turbine modes from measurements

Abstract Three methods for estimating time-varying (Hilbert-Huang transform, continuous wavelet transformation and partial Floquet analysis) one time-invariant (stochastic subspace identification) natural frequencies viscous damping ratios based on free responses are tested compared. The methods’ performance sensitivities to several system characteristics with a series of simulated responses. It is shown that, the group three methods, most suitable Hilbert-Huang transform unsuitable tested. Of four tested, stochastic identification method be robust measurement noise, but its estimates contain notable bias error due short time used. Natural edgewise blade modes estimated measured from single output location. median these have been calculated almost same.