Methodology for grid voltage unbalance compensation appling a two-converter series DFIG topology

This paper presents a new control strategy for the DFIG replacing the conventional Grid Side Converter for a series one, namely series grid side converter (SGSC). The control strategy for operation under grid voltage unbalance intends not only the ideal machine operation, but also to attenuate the grid voltage unbalance. This compensation is performed injecting unbalanced currents in the point of common coupling (PCC). The SGSC promotes a higher operational capacity during grid disturbances as voltage unbalances. The proposed methodology uses the machine electromagnetic power equation decomposed by the symmetrical components to obtain a relationship between the rotor negative sequence current and the stator negative sequence voltage, where the oscillating components of the electromagnetic power are zero. Appling this relationship is possible to reduce the electromagnetic torque oscillations when injecting negative sequence current by the machine stator.