*2.1. General Objective*

The typical layout of a MW-class PV farm system is illustrated in Figure 1. A large-scale PV array contains distinct inverters and transformers. In regard to compensation, when an ancillary device for renewable system is considered, the installation location should be at the main bus or sub-station of the PV system. As shown in the figure, a common area is formed by linking the MW-scale solar power generation arrays with a storage device in the DC section. The main purpose is to define possible impact from current flows in the DC section, and preparing a control method for supporting the compensation process in integrated ESS.

**Figure 1.** A megawatt (MW)-scale photovoltaic/energy storage system (PV/ESS) for common direct current (DC) configuration.

In various research, large-scale PV plants are modeled with a lumped single generator, by neglecting current flow from each PV module. In terms of power system analysis, this modeling method is fast and useful in identifying the influence of generated power from farm network. However, as mentioned in Ref. [21], a detailed model construction is necessary when deriving a concrete compensation plan is required through confirmation of an instantaneous production of a PV system. It is necessary to select the available topology for industrial use, when implementing DC power flow with a focus on large PV configurations. Generally, to secure the robustness in terms of power extraction, a single MW PV array is connected to the grid through a central inverter topology [22]. With the topology, a mega-voltage ampere (MVA) class DC/AC inverter can accommodate several thousands of PV panels. However, unlike other topologies, the central topology exhibits low levels of flexibility and high mismatching losses due to its huge configuration characteristics. New PV panels for the MW class even consider mismatching losses in PV array arrangemen<sup>t</sup> through the use of several re-configuration techniques, as described in Ref. [23].

In DC distribution network research, several studies have been conducted in regards to the e ffects of DC current owing to PV modules. Authors in Refs. [24,25] focused on large-scale integration of the PV system in terms of grid impact such as voltage drop and defined capacity range of a suitable PV generation system. There has been demand in PV module about a DC current analysis. Refs. [26,27] consider actual losses due to a realistic maximum power point tracking (MPPT) errors in large-scale PV system. Reference [23] pursues minimizing mismatching loss by adopting module sorting techniques. A more detailed interpretation is required to establish a more accurate ESS compensation plan in view of the instantaneous power of the internal module. It is likely that the common DC system mentioned in this section will be a ffected by the current generated by each module, and the resulting DC voltage variation a ffects the existing ESS control schemes. In the case of PV, since the power generated by each module varies continuously, the voltage calculation of each point through the power flow analysis can be undertaken instantly. By utilizing this values, e ffective control method for internal ESS can be derived. As a result, data from the external environment can be used to derive its impacts on the internal electric network to use at the main controller. These measures can be useful in the structure of modern PV managemen<sup>t</sup> systems that use various sensors to obtain environmental information or utilize predictions.
