tailieunhanh - From Turbine to Wind Farms Technical Requirements and Spin-Off Products Part 8

Tham khảo tài liệu 'from turbine to wind farms technical requirements and spin-off products part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Power Fluctuations in a Wind Farm Compared to a Single Turbine 129 The shadowed area in Fig. 19 indicates the 5 25 50 75 and 95 quantiles of the time delay T between the oscillations observed at the turbine and the farm output. Fig. 19 shows that the time delay is less than half an hour days the 90 of the time. However the time delay experiences great variability due to the stochastic nature of turbulence. Wind direction is not considered in this study because it was steady during the data presented in the chapter. However the wind direction and the position of the reference turbine inside the farm affect the time delay T between oscillations. If wind direction changes the phase difference p 2nf T can change notably in the transition frequency band leading to very low coherences in that band. In such cases data should be divided into series with similar atmospheric properties. At frequencies lower than 40 cycles day the time delays in Fig. 19 implies small phase differences Ap 2nf T colorized in light cyan in Fig. 20 and fluctuations sum almost fully correlated. At frequencies higher than 800 cycles day the phase difference Ap 2nf T usually exceeds several times 2n radians colorized in dark blue or white in Fig. 20 and fluctuations sum almost fully uncorrelated. It should be noticed that the phase difference Ap exceeds several revolutions at frequencies higher than 3000 cycles day and the estimated time delay in Fig. 10 has larger uncertainty Ghiglia Pritt 1998 . Thus the unwrapping phase method could cause the time delay to be smaller at higher frequencies in Fig. 11. This methodology has been used in Mur-Amada Bayod-Rujula 2010 to compare the wind variations at several weather stations wind speed behaves more linearly than generated power . The WINDFREDOM software is free and it can be downloaded from . 7. Conclusions This chapter presents some data examples to illustrate a stochastic model that can be used to estimate the smoothing effect .

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