In this paper, a doubly fed variable speed wind induction generator connected to the grid associated to a flywheel energy storage system (FESS) is investigated. The dynamic behaviour of a wind generator, including the models of the wind turbine (aerodynamic), the doubly fed induction generator (DFIG), a ac/ac direct converter, the converter control (algorithm of VENTURINI) and the power control of this system, is studied. Also investigated is a control method of the FESS system, which consists of the classical squirrel-cage induction machine supplied off the variable speed wind generator (VSWG) through a rectifier-inverter cascade arrangement. Simulation results obtained on the basis of the dynamic models of the wind generator are presented, for different operating points, to demonstrate the performance of the proposed system. (C) 2007 Elsevier Ltd. All rights reserved.