Control strategy for a Doubly-Fed Induction Generator feeding an unbalanced grid or stand-alone load

In this paper, the control systems for the operation of a Doubly-Fed Induction Generator (DFIG), feeding an unbalanced grid/stand/alone load, are presented. The scheme uses two back-to-back PWM inverters connected between the stator and the rotor, namely the rotor side and stator side converters respectively. The stator current and voltage unbalances are reduced or eliminated by injecting compensation currents into the grid/load using the stator side converter. The proposed control strategy is based on two revolving axes rotating synchronously at +/-omega(e). From these axes, the d-q components of the negative and positive-sequence currents, in the stator and grid/load. are obtained. The scheme compensates the negative-sequence currents in the grid/load by supplying negative-sequence currents via the stator side converter. Experimental results obtained from a 2-kW experimental prototype are presented and discussed in this work. The proposed control methodology is experimentally validated for stand-alone and weak grid-connected conditions and the results show the excellent performance of the strategy used. (C) 2008 Elsevier B.V. All rights reserved.