Considerations on the aggregation of harmonics produced by large wind farms

One aspect of assessing the harmonics tolerated by a power system is the estimation of the aggregation or sum of harmonics arising from the various sources. The estimation of harmonics is not exact or uniform, since there will be unpredictable variations in either the non-linear sources and/or parameters of the system which affect the summation. The combination of a number of harmonic sources will generally lead to less than the arithmetic sum of the maximum values due to uncertainty of magnitude and phase angle. Hence the resulting summation is difficult to estimate accurately. In this paper the harmonic summation caused by large wind farms with harmonic sources is investigated. The work verifies, by computational simulations, the harmonic aggregation in the point of common coupling (peC) of a typical wind farm under study by the Brazilian Systems Operator. Results show that the harmonic summation estimates for different conditions. The results are also compared with the lEe 61400-21 recommended aggregation factors. The results indicate that aggregation of harmonics at the point of common coupling cannot be easily generalized. The topology of the wind farm, the type of electronic converter, the wind variations, the frequency range and the upstream supply system impedance play a very role in the determination of the aggregation coefficients.