Hybrid Control Strategy for a Doubly Fed Induction Generator in Medium Voltage Wind Power System under Unbalanced Grid Conditions

This paper investigates control algorithms for a doubly fed induction generator with a back-to-back three-level neutral-point clamped voltage source converter in medium voltage wind power system under unbalanced grid conditions. Negative sequence control algorithms to compensate for unbalanced conditions have been investigated with respect to four performance factors; fault ride-through capability, instantaneous active power pulsation, harmonic distortions and torque pulsation. The control algorithm having zero amplitude of torque ripple shows the most cost-effective performance concerning torque pulsation. The least active power pulsation is produced by control algorithm that nullifies the oscillating component of the instantaneous stator active and reactive power. Combination of these two control algorithms depending on the operating requirements and depth of grid unbalance presents most optimized performance factors under the generalized unbalanced operating conditions leading to high performance DFIG wind turbine system.