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A PI-based control algorithm to govern the net reactive power flowing between wind farms composed of doubly fed induction generators (DFIG) and the grid is proposed in this paper. The motivation underlying consists in demonstrating that secondary voltage control strategies may take advantage of such wind farms as if they were continuous reactive power sources. For that purpose, the local control structure of DFIGs is first described in some detail. The open-loop behavior of a 33 660-kW DFIG wind farm regarding the net power factor is then analyzed via simulation. Based on this study, a net reactive power control algorithm is devised for wind farms made up exclusively of DFIGs. Experimental results obtained by testing it both local and remotely, over a real wind farm located in Navarre-northern Spain-are also provided. In particular, net reactive power set-points supplied remotely to the wind farm are derived by an Optimal Power Flow (OPF) algorithm running at the operation central office of the utility company.