The basic objective of microgrid primary control is to preserve microgrid stability. On the other hand, microgrid secondary control has been proposed for ensuring reactive power-sharing and restoring the frequency and voltages of the microgrid. Therefore, this paper presents a complete model for evaluating the combined impact of primary and secondary control actions on microgrid domain of stability since the impact of the secondary control design on the domain of stability of the microgrid has not been addressed. Further, the developed model is used to assess the impact of reactive power-sharing, secondary controller design parameters, and communication delay on the domain of stability of the microgrid. The domain of stability is a supportive tool for determining the stable operating range for different microgrid droops. Simulation results have been obtained to validate the developed model and the domain of stability analysis. These results demonstrated that secondary control actions have a significant influence on the domain of stability of the microgrid, and thus it is important to consider the secondary control design in the determination of the microgrid’s stable range. Moreover, it has been demonstrated that primary control gains can be severely constrained by reactive power sharing gains.

The most popular approach used in controlling inverter-based microgrids is the droop control technique, characterized by its plug-and-play capability and independence from communication requirements. The control parameters, at the top of which the active and reactive droop gains, m_p and n_q , respectively, have been recently studied, evaluating their impact on stability. Furthermore, the stability domain chart is plotted in the m_p,max - n_q plane identifying the stable range of the microgrid, enabling the microgrid operator to choose the desired stable operating point based on frequency, voltage, and power-sharing requirements. However, the microgrid is prone to abnormal conditions, such as network disconnection, distributed generator (DG) disconnection, and load disconnection, that also affect microgrid stability. Hence, this can have an impact on the stability domain and, consequently, the choice of droops for stable operation. Therefore, in this paper, several stability domain charts are proposed, considering all various contingencies. The proposed network disconnection, DG disconnection, and load disconnection domain charts have been combined to generate an overall stability domain chart considering N - 1 contingency. The proposed N - 1 contingency chart is of crucial importance in considering the microgrid stability for both normal and abnormal operations. N - 1 contingencies can be frequent in microgrid operation due to microgrid limited space and power nature. Hereby, the inclusion of their impact on microgrid stability provides better guidance for the tuning of the control parameters. Moreover, the proposed chart is tested and validated using time-domain simulations on MATLAB, considering different operating points. The simulation results highlight the significance of the stability domain chart for selecting the DG droop gains to maintain the microgrid stability considering N - 1 contingency. Further, real-time validation of the proposed domain of stability through OPAL-RT setup is analyzed to confirm the ability of practical controllers to respond to microgrid variations conditions in real-time operation.