VSC-based LVDC distribution network with DERs: Equivalent circuits for leakage and ground fault currents evaluation

In this paper a new, general methodology for leakage and ground fault currents evaluation in grid-connected, low-voltage DC microgrids is introduced. Modified sequence equivalent circuits are considered, generalizing traditional AC power systems analysis. For three-phase systems, a modified Clarke transformation and, for two-wire systems, a modified modal transformation are introduced. These transformations, applied to a hybrid AC/DC system, allow building a modal equivalent circuit of the whole system, constituted by two coupled sub-circuits. The proposed equivalent circuits are intended as general time-domain models and are suitable for both steady-state and transient analysis. This approach highlights the whole system topology and allows evaluating the influence of active and passive components on leakage and ground fault currents. The proposed methodology is experimentally verified and, successively, applied to a hybrid AC/DC microgrid including DERs and storage devices.