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Tham khảo tài liệu 'from turbine to wind farms technical requirements and spin-off products part 7', 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 109 linearly averaged periodogram in squared effective watts of real power per hertz . The trend is plotted in thick red the accumulated variance is plotted in blue and the tower shadow frequency is marked in yellow. The instantaneous output of a wind farm or turbine can be expressed in frequency components using stochastic spectral phasor densities. As aforementioned experimental measurements indicate that wind power nature is basically stochastic with noticeable fluctuating periodic components. Fig. 3. PSDP f parameterization of active power of a 750 kW wind turbine for wind speeds around 6 7 m s average power 190 kW computed from 13 minute data. The signal in the time domain can be computed from the inverse Fourier transform P t T r P f ẹj df dT rP f cos12nft v f I df 2 - P f P -f 0 1 J An analogue relation can be derived for reactive power and wind both for continuous and discrete time. Standard FFT algorithms use two sided spectra with negative frequencies in the last half of the output vector. Thus calculus will be based on two-sided spectra unless otherwise stated as in 2 . In real signals the negative frequency components are the complex conjugate of the positive one and a Vi scale factor may be applied to transform one to two-sided magnitudes. b Spectral power balance in a wind farm Fluctuations at the point of common coupling PCC of the wind farm can be obtained from power balance equations for the average complex power of the wind farm. Neglecting the increase in power losses in the grid due to fluctuating generation the sum of oscillating power from the turbines equals the farm output undulation. Therefore the complex sum of the frequency components of each turbine Pturbine i f totals the approximate farm output Pfarm f 110 From Turbine to Wind Farms - Technical Requirements and Spin-Off Products N NN turbines d Pf turbines turbines Pfarm f dP Pturbine i f niPturbine i f niPturbine i f P 3 i
