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Wind energy is gaining the most interest among a variety of renewable energy resources, but the disadvantage is that wind power generation is intermittent, depending on weather conditions. Energy storage is necessary to get a smooth output from a wind turbine. This paper presents a new integrated power generation and energy storage system for doubly-fed induction generator based wind turbine systems. A battery energy storage system is connected to the DC link of the back-to-back power converters of the doubly-fed induction generator through a bi-directional DC/DC power converter. The energy storage device is controlled so as to smooth out the total output power as the wind speed varies. Control algorithms are developed for the grid-side converter, rotor-side converter and battery converter, and are tested on a simulation model developed in MATLAB/Simulink. The model contains a DFIG wind turbine, three PWM power converters and associated controllers, a DC-link capacitor, a battery, and an equivalent power grid. Simulation studies are carried out on a 2MW DFIG wind turbine and the results suggest that the integrated power generation and energy storage system can supply steady output power as the wind speed changes.