EXTRACTING TIME-VARYING MEAN OF THE NON-STATIONARY WIND SPEEDS BASED ON WAVELET TRANSFORM (WT) AND EMD

According to Gramer theorem,the non-stationary wind speed may be decomposed into a deterministic time-varying mean wind speed component plus a stationary fluctuating wind speed component with zero mean value.Time-varying mean wind speed is able to characterize the non-stationary performance of wind speed.Hence,its correct extraction may make the analysis of non-stationary wind speed easier.In the present paper,the appropriate levels for decomposing the time-varying mean wind speed were quantitatively determined by the saltation of simple scale wavelet energy.The accurate time-varying mean wind speed was then gained by the inverse discrete orthogonal wavelet transforms of approximate coefficients in this level.The numerical results indicate that the obtained time-varying mean wind speed based on wavelet transform is more accurate and realistic than that with resorting to the empirical mode decomposition approach.