Independent operation of DFIG-based WECS using resonant feedback compensators under unbalanced grid voltage conditions

This proposed work presents a new control strategy for a Doubly Fed Induction Generator (DFIG) under unbalanced network voltage conditions. This proposed control strategy provides an independent operation of the Rotor Side Converter (RSC) and Grid Side Converter (GSC) for a Doubly Fed Induction Generator (DFIG) based wind energy conversion system (WECS) under unbalanced grid voltage conditions. The DFIG control targets during network unbalance, such as reducing stator current unbalance, torque, and power pulsations minimization, are identified. The RSC is controlled to achieve four different control targets, including balanced stator current, sinusoidal rotor current, smooth stator active and reactive powers, and constant DFIG electromagnetic torque. The GSC is controlled to keep the DC voltage at a constant value. The resonant feedback compensator (R) is added with proportional integral (PI) control to make PIR and this controller is used to decomposition of the positive and negative sequence component and calculations of the rotor negative current references can be avoided. Another similar compensator is used in the GSC to suppress the DC voltage fluctuates and remove the GSC reactive power oscillations without the stator or rotor power information. The proposed method can make the RSC and GSC available to an independent operation with a simple implementation for higher reliability.