چكيده به لاتين
Application of power electronic converters in wind turbines results in generation of harmonic and interharmonic. Also, the switching of converters results in turbines active output power distortions. Harmonic interaction of wind farms with external grid, harmonic propagations in it and amplification of these propagations due to resonance of underground transmission cables, can leads to increase in power quality problems. Hence, this thesis was planned to carry out a harmonic survey on these wind farms.
Harmonic emission situation from individual wind turbines as well as at the point of common coupling (PCC), containing harmonic current and voltage spectra, its phasor analysis, and dependence of harmonic emission on wind farm output power is addressed. Individual frequency components depend on the power production in different ways: characteristic harmonics are independent of power; interharmonics show a strong correlation with power. The impact on the grid, with reference to permissible levels of voltage distortion, is biggest for the interharmonic components. It is concluded that the power production is not the only factor determining the current emission of a wind energy conversion system.
A method is provided for study and classification of conventional current harmonic emissions in a wind farm based on transfer function and harmonic modeling of wind farm components in frequency domain in order to evaluate the harmonic contributions of each wind turbines at point of connection as well as the contribution of external grid background harmonic voltage on each turbine current harmonic distortion. Aggregation effect of complex harmonic currents from individual wind turbines through the collector network, evaluated based on transfer function: complex harmonic current emissions originated from ten wind turbines, at the collection grid after aggregation, transmitted to the external grid with severity and infirmity. The complex currents are spread around a center point. For interharmonics, this center corresponds to the origin of the complex plane. For integer harmonics, this center is offset from the origin.. In addition, transfer function is used to decomposes primary emission from secondary emission. In order to evaluating aggregation effect of primary and secondary emission, accuracy of these function will be increased by average modeling of type III wind turbine converters.
Keywords: Doubly-fed induction generators,Wind farm, Harmonics, Active power, Primary and secondary emission, Transfer function, Resonance, Harmonics aggregation, Average modeling.
