Unbalanced-Grid-Fault Ride-Through Control for a Doubly Fed Induction Generator Wind Turbine with Series Grid-Side Converter

The grid codes now require doubly fed induction generator (DFIG) wind turbines having the “low voltage ride-through (LVRT)” capability. However, a traditional DFIG with a partially rated back-to-back converter has inherent difficulties to ride through the grid faults, especially for the unbalanced grid faults. Modifications to the traditional DFIG configuration for ride-through have become necessary. A DFIG system with series grid-side converter (SGSC) has an excellent potential for voltage dips tolerance. This paper analyzes the reasons of a DFIG system with SGSC for ride-through and presents a control scheme for operation under unbalanced grid faults conditions. During grid faults, the each component of the generator’s stator flux is effectively controlled through the SGSC. Also, the stator and rotor currents are further restricted by controlling the rotor-side converter (RSC) to reduce the absorbing energy from wind turbine. Then, successful ride-through of a DFIG system with SGSC under all types of severe unbalanced grid faults at the point of common coupling (PCC) are achieved with reduced electromagnetic torque oscillation. The proposed control scheme is validated by means of simulations. Key-Words: Doubly fed induction generator (DFIG), series grid-side Converter (SGSC), unbalanced grid fault, wind turbine, low voltage ride-through (LVRT), wind power generation, voltage dips, voltage sags