*4.1. Simulation Design*

In order to assess the proposed control method, a detailed simulation is conducted using a power-system computer aided design (PSCAD). Figure 6 shows a layout of the PV connected

distribution network, that utilizes the linked DC section. The PV generation system in the network has a nominal power capacity of 400 kVA. To verify the proposed method, a single PV generation system includes 120 parallel/40 series modules. The PV system is connected to the displayed distribution network by utilizing the central inverter topology. The DC network also includes the ESS model to verify the proposed reference modification method. The distance data about the distribution network is reflected in pi-line which is the base model in PSCAD/EMTDC. The network information, which is used for utility grid construction, is shown in Table 1 including the PI-line distances in Figure 6.

**Figure 6.** Simulated distribution network including MW-scale PV/ESS.


**Table 1.** Numerical data for the simulation.

Figure 7 describes the simulations of the designed PV production. PV system extracts real power based on the radiation data as per the specific coefficient values. A small variation of the extracted power could affect the operation of the connected ESS. To check ESS control effects under certain conditions, unexpected variations need to be checked. Table 2 includes applied load parameters for the case studies. The main objective of the simulation is to confirm that the proposed method shows better reliability compared to rated voltage-based control. The voltage controller is configured based on an existing solar-ESS combined control, which takes into account the sensitivity between voltage and power production [34]. The method generally operates in combination with on-load tap changer (OLTC), ye<sup>t</sup> it depends on the characteristics of the connected power system. Therefore, in this paper, we try to compare the results when only the main controller was applied. To check ESS

operation, a number of discrete load variations were designed for each scenario. The simulation mainly considers the charging/discharging processes to confirm profile accuracy in regards to reference signal. The reference signal is designed to change depending on the load condition, while the configured case studies and entire simulation time is set to 10 s including the start-up time. Assuming abrupt load variation, a number of orders changing sections (for charging and discharging) are designed for the simulation. A few of the load changes are executed by stages as displayed in Figure 8. The momentary load changes (75 kW) generates a demand about the order change for reducing the distribution network burden.

**Figure 7.** Basic PV production in case study.


**Table 2.** Simulated case study description.

**Figure 8.** Simulated load variation in case study.

Without ESS, the connected substation should supply the required power based on the change of the distribution network. However, with ESS, a distribution system operator would attempt to cover the unexpected variation through the support of ESS due to operation responsibility (i.e., rate of power change). This forms the basis of the operational objective of the ESS in this scenario. The total power supplied from the grid with non-ESS condition is shown in Figure 9. Based on this condition, ESS charging/discharging would be handled through applied methods. The basic algorithm using the power command and the rated voltage is entered to obtain an effect firstly, and a comparison analysis with the proposed use is advanced.

**Figure 9.** Power supplied quantity from main grid (non-ESS).
