**2. Structure and Modeling of Island DC Microgrid**

The structure of an island DC microgrid is depicted in Figure 1, which mainly composes of four parts: (1) distributed resources (PV and wind turbine); (2) eEnergy storage unit; (3) various types of load (mainly divided into CPLs and resistive load); and (4) line impedance. Subsystems in the DC microgrid can also be divided into power control unit and constant voltage control unit according to their control mode [19]. The purpose of power control is to ensure that distributed generators inject constant power or maximum power into the system. In this paper, MPPT (maximum power point tracking) control was used for distributed generators such as wind turbines and PVs to achieve maximum power utilization. The constant voltage unit is aimed at stabilizing bus voltage [23]. For the energy storage unit, a droop control method is applied to the DC bus voltage [24].

**Figure 1.** Typical configuration of an island direct current (DC) micro grid. **Figure 1.** Typical configuration of an island direct current (DC) micro grid.
