Performance Improvement of DFIG Wind Turbine Using Series Grid-Side Converter under Unbalanced Grid Voltage and Voltage Sag Conditions

Under unbalanced grid voltage conditions, the doubly fed induction generator (DFIG) stator voltage, in addition to positive sequence component has negative sequence component. The negative sequence component causes oscillations in the output power, electromagnetic torque and DC link voltage at twice the supply frequency. This paper presents a modified configuration of DFIG with series grid-side converter (SGSC) and its control system, which is suitable not only for unbalanced grid voltage conditions, but also for small voltage sags. The proposed configuration improves all the DFIG signals under unbalanced grid voltage and small voltage sag conditions without needing additional DC link capacitor or energy storage unlike other methods. The control system includes negative and positive sequence controllers which make the stator voltage balanced and keep it constant at the nominal value. Matlab/Simulink is used for simulation of a 1.5-MW DFIG and the results demonstrate the good efficiency of the proposed scheme.

کلیدواژه ها:

doubly fed induction generator (DFIG) ، unbalanced voltage ، voltage sag ، series grid-side converter (SGSC)