I. Introduction
The traditional control in the rotating reference frame (RRF) (dq) of three-phase voltage source converters (VSCs) assumes that grid voltages are reasonably balanced. However, unbalances appear frequently in practical applications of grid-connected power electronic converters. When the grid voltage is not balanced, a second harmonic component appears in the instantaneous active power and hence dc-link voltage of the converter [1]. This degrades the performance and stability of the VSC. The performance of a VSC operating under unbalanced, reduced voltage, or fault conditions can be improved by dual-sequence current controllers [2]–[5].