The present study proposes feedforward angle droop strategy based on discrete time mathematical model for islanded operation of dispatchable distributed generation (DG) units, connected directly or through voltage source converters to the microgrid. These units should supply their local and common loads. To improve the robustness of the proposed control strategy in imbalance and transient conditions, a combination of current and repetitive controller (RC), with time varying sampling period, is used. High angle droop gain ensure proper load sharing between DG units even in weak networks, but it has negative effects on grid stability. Therefore adaptive control strategy is used to solve the problems of uncertainties and also to improve the reliability of control strategy in load sharing with high angle droop coefficients. Furthermore, to reduce harmonics caused by the converters’ switching, a LCL filter is used. Performance of the proposed control strategy is demonstrated for islanded microgrid, with different types of DG units, loads and conditions through simulation studies in the Digsilent Power factory software environment.

Keywords: Islanded operation, Angle droop, LCL filter, Repetitive adaptive controller, High droop gain