Abstract
In the last decade, wind generation techniques have been actively developed, and wind farms comprising doubly-fed induction generators (DFIGs) have been widely deployed. As a result of the increasing penetration of wind generation, the output power of DFIGs requires adjustment to ensure an adequate supply of reactive current under fault conditions. Many studies show that the reactive capability of a DFIG is constrained by the rotor current and terminal voltage. However, the power adjustment of DFIGs changes the grid power flow and the terminal voltage of DFIGs due to the coupling between DFIGs and the grid. The permissible power range of DFIGs also changes because of the terminal voltage variation. The DFIG–grid coupling has not been considered, and the permissible power range is not accurate. The control methods based on the existing permissible power range do not maximize the power controllability of DFIGs. In this paper, the fault power characteristics of DFIGs under the constraints of rotor current and rotor speed are analyzed on the basis of a fault model. The permissible power range of DFIGs with consideration of internal and external constraints is established by analyzing the terminal voltage under the effect of the grid power flow. A control method for maximizing fault voltage is proposed on the basis of the established permissible power range. The simulation results verify the accurate calculation of the permissible power range. The power controllability of DFIGs could be fully utilized to improve fault voltage by adopting the proposed method.
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