A comprehensive analysis study about harmonic resonances in megawatt grid-connected wind farms

This paper presents a comprehensive analysis technique about harmonic resonance issues in megawatt grid-connected wind farms where the doubly fed induction generator (DFIG) is used. Wherein, firstly, the background theories of the series resonance, parallel resonance and their impacts on the electric system are described. Moreover, a suitable equivalent circuit of typical grid-connected DFIG wind farms for analyzing impedance in the frequency domain is proposed. Then, mathematical formulas are introduced detail to determine exactly orders and amplifications of the voltage and current distortions on both the medium-voltage (MV) bus and low-voltage (LV) bus. Lastly, results obtained from the proposed equivalent circuit and impedance analysis technique are compared to other results achieved with the detailed wind farm simulated in MATLAB/SimPowerSystems. As well, many different operation cases of the illustrative grid-connected DFIG wind farm, including parametric variations, are also examined to evaluate the accuracy and effectiveness of the proposed analysis technique..