Adaptive Droop Control for Stability Enhancement in Islanded DC Microgrids with CPLs

Modern DC Microgrids (DC-MGs) typically comprise renewable generation units, batteries, and loads interconnected via power converters. Loads with stiffly regulated converters may behave as Constant Power Loads (CPLs) and exhibit negative incremental impedance, which can decrease the system's damping capability and increase the risk of instability. To address this issue, droop gains can offer a proper potential to enhance the grid's dynamic behavior. Thus, this paper proposes a decentralized droop-based algorithm to adjust the droop gains adaptively to not only provide good voltage regulation and accurate current sharing among units but also sustain the grid far from the instability margin. To this end, the droop gains' upper bound necessitated to ensure stable operation will be determined, considering the in-service CPLs. Then, based on this upper bound, the droop gain for each unit can be obtained. The stability of the DC-MG is analyzed by computing the system's eigenvalues using a small-signal analysis. The effectiveness of the proposed approach has been evaluated through simulation scenarios using MATLAB®/Simulink.