Improved control scheme of stand-alone DFIG-based wind energy conversion system with battery energy storage system

An improved control scheme for stand-alone DFIG-based wind energy conversion system is proposed. The intermediate DC-link of back-to-back PWM converter is supported with a battery energy storage system to smooth the fluctuation of power caused by the variation of wind speed and loads. A three-phase four-leg converter is employed as the Stator-Side Converter (SSC) to provide a path for the zero-sequence current. Based on the modified topology, the stator voltage of DFIG is directly controlled by the SSC. And the rotor speed of DFIG is regulated by the rotor-side converter for maximum power point tracking. Modified repetitive controllers incorporated with the state-feedback controllers are adopted for the SSC to ensure the desirable stator voltage even under the unbalanced loads or non-linear loads conditions. The proposal avoids the complicated operation of the harmonic extraction, and the positive-and negative-sequence current decomposition, which is verified by the simulation results.