*2.2. Conceptual Design*

Figure 2 represents a conceptual control plan of the proposed method. The entire power from DC-based source is transferred to the connected grid through a main PCS. The ESS is integrated into a common DC link using a DC/DC converter. Since the compensation devices in these structures should be located at the front of the main PCS, the power flow from DC generators (PV or wave) should pass through the junction of the ESS [28]. Through this flow, the integrated storage device is directly a ffected by the electrical conditions with respect to the voltage level which is among the main reference signal of the control process. The main purpose of the compensation devices is to store excess output power (above the reference signal) and utilize a bi-directional PCS to discharge the stored energy on the operators' request. This paper describes DC power flow analysis, including DC network characteristics for PV generators. Section 2 covers a basic system description.

**Figure 2.** Power control concept of ESS-combined PV system.

### *2.3. Alternating Current*/*Direct Current (AC*/*DC) Hybrid System*

General voltage-sourced converter (VSC)-based structures are established at the front of generation system, which means that the generated power must pass through a DC section through its own converter. Therefore, as described in Ref. [29], the power supply from combined DC network could

experience more ohmic losses compared to other single generation system. There are several studies on the DC farm topologies to increase efficiency and mitigate these issues as a result [30]. The conventional DC-based farm have extended the available farm scale through the increase in number of the sources and boosting level of the classified voltage.

The model utilized in this paper focuses on coupled power resources structure constructed in DC. Once the ESS is planned to attach to the structure, it should be placed in front of the main sub-system and follow the operators' order. The ESS applications applied in the DC section are based on improved usability. However, the electrical flow in the low voltage section can result to unstable voltage conditions in terms of compensation device usage. As a compensation device in the common DC network is expected in several renewable energy sources, an advanced technique based on DC analysis is required to maintain the system's performance.
