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The increasing penetration of the distributed energy resources (DER) in the power grid, which, while having significant advantages, also pose significant challenges. The behaviors of DERs differ from those of synchronous generators, particularly in abnormal conditions. For this reason, the power grid enforces grid codes to ensure that DERs perform properly in different conditions. For instance, short circuit faults and unbalanced grid voltage are severe transient events that inverters need to be able to pass through without disconnecting from the grid. Furthermore, the inverters are required to support the grid voltage by regulating the active and reactive power injections. This article proposes a voltage support control scheme to support grid voltage during asymmetrical voltage drop by utilizing an optimization problem. In this optimization problem, the active and reactive powers injected into the grid will be obtained optimally by considering constraints such as instantaneous active and reactive power oscillation magnitudes and peak current limitation. To aid in this purpose, the corresponding mathematical formulations such as instantaneous active and reactive power oscillation magnitudes will be obtained by using the currents and voltages in stationary reference frame. The proposed scheme will be verified by simulating it in MATLAB/Simulink under three different scenarios and tested on a real‐time experimental Opal‐RT platform. [ABSTRACT FROM AUTHOR]

• A new and improved secondary controller is proposed. • Control the SLB voltage quality. • Control the voltage quality of other buses of microgrid (MPQL control). • Considering DGs peak current limitations. • Simplifying the control process. This paper proposes a two-layer hierarchical control structure to realize compensation of voltage unbalances optimally in different buses of islanded microgrids. The primary layer controls the microgrid voltage and frequency. The secondary layer is used to realize the unbalance compensation of the sensitive load bus (SLB). Improvement of the voltage unbalance factor (VUF) at the SLB may lead to an increase in VUF at local buses and/or DG terminals. A complementary part is designed and added to the secondary control in order to tune the compensation portion of each DG source while limitations of VUF at DG terminals and local buses are considered too. This method realizes multi-power-quality-level control through a simple yet effective solution. Simulation results are given to demonstrate the advantages of the proposed control scheme. [ABSTRACT FROM AUTHOR]