Control methodology for compensation of grid voltage unbalance using a series-converter scheme for the DFIG

• Methodology for compensation of voltage unbalances using a DFIG based on a series converter.
• Exploits the series-DFIG scheme to avoid that voltage unbalances compromise the machine operation.
• The method also compensates voltage unbalances at the point of common coupling (PCC).

This paper proposes a control methodology for compensation of grid voltage unbalances using a new scheme of doubly fed induction generator (DFIG) based on a series grid side converter (SGSC), the series-DFIG scheme. In such DFIG scheme, the grid side converter (GSC), which is usually connected in parallel to the machine stator, is replaced by the SGSC, connected in series with the machine stator. The proposed control methodology exploits the potential of the series-DFIG scheme to avoid that grid voltage unbalances compromise the machine operation, and to compensate voltage unbalances at the point of common coupling (PCC), preventing adverse effects on loads connected next to the PCC. This methodology uses the rotor side converter (RSC) to control the negative sequence current injected through the machine stator and the SGSC to control the negative sequence stator voltage to minimize the electromagnetic torque oscillations. The proposed control methodology is validated by simulation results.