# Design of Direct Current Microgrid Converter with Cost-Effective Low-Voltage Battery Storage System
## 2 DC-DC Microgrid System Design  
Nowadays, high-power photovoltaic arrays are mostly under consideration once practical realization is provided. These arrays are mostly connected in strings; each string can provide DC bus voltage within the range of 80-560 Vdc depending on the installed power and configuration of the photovoltaic array. A high-voltage DC bus is efficient for directly connecting the inverters to the AC grid. Another possibility is a simple connection using converters with the MPPT algorithm. In this way, each string of photovoltaic array supplies a constant voltage within the common DC bus. Using proper power control with the possibility of bidirectional energy flow makes storing the energy within the battery storage system possible (see Figure 1) [6; 7; 8].  
Island systems are mainly used in remote places with no power line or where introducing an electrical connection would be complicated and economically demanding. The second aspect of island systems is independence from other energy suppliers--self-sufficiency. In general, these are power plants operating independently of the electrical distribution network. A plant can be a photovoltaic power plant, but it can also be a wind power plant, or any other type of power plant, or a combination of them, regardless of whether it uses renewable or non-renewable resources. As mentioned earlier, microgrid networks are becoming more and more popular. Above all, DC-DC microgrid networks, Figure 2, are suitable for supplying less-demanding devices, making it easier to operate and maintain the required parameters, and these are more affordable than AC microgrid networks [25].  
The presented solution represents simulation and creation, creating a working prototype of a cost-effective, compact solar energy storage system (Figure 3). Such a system should efficiently store energy from low-power solar cells and supply a home DC microgrid [11; 12]. The design can be related to new organic solar cells that provide better efficiency and flexible cell options that can be implemented in various spaces with a small area within the building complex [26]. The basic parameters of the investigated system are shown in Table 1.  
Since the system's input voltage (generated from the PV panels) varies over a wide range, and similarly, the voltage on the batteries when feeding the load can vary over a wide range, it is necessary to use two buck-boost converters. The first inverter manages the correct charging of the batteries; the second inverter manages the constant voltage for the load. This solution makes this system more compatible and stable at any level of working voltages (PV panels, batteries, and load, but within a defined safe range). Self-energy consumption can be reduced by switching it off during time intervals once solar energy is  
Figure 1: Schematic of a grid-connected solar photovoltaic system.  
unavailable. On the other hand, the output converter must be continuously operated to supply the microgrid system [27].  
This proposal aims to create a modular system that can be adapted to the requirements of a specific application. The power range, range of input and output voltages, and other parameters can be considered during the solution's design.