CONTROL STRATEGY FOR THE ROTOR SIDE CONVERTER OF A DFIG-WT UNDER BALANCED VOLTAGE SAG

This paper proposes a new control technique to improve the fault-ride through capability of doubly fed induction generators (DFIG). In such generators the appearance of severe voltage sags at the coupling point make rise to high over currents at the rotor/stator windings, something that makes necessary to protect the machine as well as the rotor side power converter. As a difference with the most extended solution, that reduces these currents by means of the connection of a crowbar circuit, this works intends to enhance the DFIGs response in such conditions without introducing extra hardware in the system. To this end, the proposed control system feedback the stator currents as the rotor current reference during the fault, until they are driven to their nominal values. The feasibility of this proposal has been proven by means of mathematical and simulation models, based on PSCAD/EMTDC, as well as experimental results from a prototype of 6kW rated power.