A New Method to Study Aggregation Effect of Harmonic Current Emissions in a Wind Farm Based on Type-III Wind Turbine Average Modeling

Assessment of complex harmonic current contribution of each wind turbines at connection point of a wind farm to the grid (primary emission) is presented in this paper. Moreover, contribution of grid background harmonic voltage distortion on harmonic current distortion (secondary emission) of each turbine is also evaluated. Both assessments are represented based on primary and secondary transfer functions and modeling of wind farm components in frequency domain. In order to increase the accuracy of these transfer functions, wind turbine impedance must also be included in transfer functions while studying aggregation effect of complex harmonic current emissions. Accordingly, a new model of primary and secondary emission transfer functions for a type-III wind turbine is proposed to study aggregation effect of harmonic currents in a wind farm. This model is based on average modeling of back-to-back converters of a doubly-fed induction generator, in order to extract total impedance of a wind turbine in its linear working range. By applying this impedance into transfer function models, if turbines emit current with identical magnitude and phase angle, then the total primary emission aggregate less than the number of turbines, and if turbines emit current with identical magnitude but uniform phase angle distribution, then the total primary emission aggregate less than square root of the number of turbines and doesn't follow square root rule.