Repetitive control of the stator-side four-leg converter in stand-alone DFIG-based wind energy conversion system

An improved back-to-back PWM converter topology is proposed for the stand-alone DFIG-based wind energy conversion system (WECS). The intermediate DC-link is supported with a battery energy storage system (BESS) in order to feed steady and uninterrupted power to custom load under varying wind speeds; a three-phase four-leg converter is employed as the stator-side converter to provide a path for the zero-sequence load current. Based on this topology, the stator voltage could be controlled by the stator-side converter (SSC), and the rotor speed is regulated by the rotor-side converter (RSC) for maximum power point tracking (MPPT). The control scheme incorporating repetitive control and state-feedback control is adopted for the stator-side converter to ensure sinusoidal stator voltage for all types of loads including balanced, unbalanced, linear and non-linear in any arbitrary combination. This proposed method avoids the tedious calculation for the harmonic extraction and the positive and negative sequence decomposition. The Simulation results verify the correctness and feasibility of the system.