The concept of microgrid hierarchical control is presented, recently. In this paper, a hierarchical scheme which includes primary and secondary control levels is proposed for islanded microgrids. The primary control level consists of DG local controllers. Local controller of each DG comprises active and reactive power controllers, virtual impedance loop and voltage and current controllers. The secondary level is designed to compensate the voltage unbalance at the load bus (LB) of the islanded

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... crogrid. Also, restoration of LB voltage amplitude and microgrid frequency to the rated values is considered in the secondary level. These functions are achieved by proper control of distributed generators (DGs) interface converters. The presented simulation results show the effectiveness of the proposed control structure in compensating the voltage unbalance and restoring the voltage amplitude and system frequency.