Methodology for Grid Current Unbalance Compensation Appling DFIG as a Parallel Active Filter

This paper presents a new control strategy for the DFIG working under grid voltage unbalance, intending not only the ideal machine operation, but also to compensate the current unbalance in the point of common coupling (PCC). Models that allow the DFIG to inject negative sequence current in the grid to compensate unbalances in the PCC have been already proposed, but they are limited by the residual power of the Grid Side Converter (GSC) or by the oscillations in the electromagnetic torque when the Rotor Side Converter (RSC) control is used. To overcome these limitations, this paper proposes a control that not only injects negative sequence current by the machine stator but also sets the stator negative sequence voltage, reducing the oscillations in the electromagnetic torque. A third converter is coupled to the machine terminals to allow the stator voltage control. Therefore, the use of the proposed control reaches two objectives simultaneously, the support to the grid power quality, and the ideal operation of the machine.