Control strategies of three-phase distributed generation inverters for grid unbalanced voltage compensation

The high penetration level of power electronics interfaced Distributed Generation (DG) systems creates great ancillary services potential through the DG interfacing converters (IFCs) such as the grid unbalanced voltage compensation. However, the unbalanced voltage compensation may cause adverse effects on the IFCs´ operation such as output active power oscillation and DC link voltage variations. Moreover, since the compensation is realized through the available rating of IFCs, it is equally important to consider the effectiveness of control strategy for unbalanced voltage compensation. Considering these challenging issues, two grid unbalanced voltage compensation strategies for three-phase power electronics interfaced DG system are proposed in this paper. Specially, the first control strategy aims at minimizing the IFC´s active power oscillation and reducing the adverse effects of unbalanced voltage compensation on IFC´s operation. The second control strategy focuses on the effectiveness of unbalanced voltage compensation by controlling IFC´s negative sequence current to be in-phase with the grid negative sequence current. Performances of the two proposed control strategies under different grid conditions and IFC operating conditions are studied. Finally, validity of proposed strategies is verified by experimental results.