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A dc series-parallel wind farm was proposed as an alternative to an ac wind farm. But, the operation of such a wind farm results in significant wind turbine (WT) output voltage variation, which may lead to severe stress being seen by the turbine capacitors. The output voltage variation problem is demonstrated and rigorously analyzed with proposed power flow calculation. In order to mitigate the voltage variation a dc WT with integrated storage along with strategies for control and storage sizing is proposed. The time domain simulation results for 120 MW 2 × 6 dc series-parallel wind farm shows that a large voltage variation, with maximum value reaching close to 2 p.u and low voltage of about 0.2 p.u, is obtained when WT output voltage is not limited. The power input variation of a single turbine affects voltages and currents of all the WTs in the wind farm. A 48 kWh storage integrated with the WT appears to significantly alleviate the WT voltage variation.
Bahirat et al. (Thu,) studied this question.