DC Bus Voltage Selection for a Grid-Connected Low-Voltage DC Residential Nanogrid Using Real Data with Modified Load Profiles

Abstract

This study examines various low voltage levels applied to a direct current residential nanogrid (DC-RNG) with respect to the efficiency and component cost of the system. Due to the significant increase in DC-compatible loads, on-site Photovoltaic (PV) generation, and local battery storage, DC distribution has gained considerable attention in buildings. To provide an accurate evaluation of the DC-RNG’s efficiency and component cost, a one-year load profile of a conventional AC-powered house is considered, and AC appliances’ load profiles are scaled to their equivalent available DC appliances. Based on the modified load profiles, proper wiring schemes, converters, and protection devices are chosen to construct a DC-RNG. The constructed DC-RNG is modeled in MATLAB software and simulations are completed to evaluate the efficiency of each LVDC level. Four LVDC levels—24 V, 48 V, 60 V, and 120 V—are chosen to evaluate the DC-RNG’s efficiency and component cost. Additionally, impacts of adding a battery energy storage unit on the DC-RNG’s efficiency are studied. The results indicate that 60 V battery-less DC-RNG is the most efficient one; however, when batteries are added to the DC-RNG, the 48 V DC distribution becomes the most efficient and cost-effective option.

Keywords

• direct current (DC) distribution
• residential nanogrid (RNG)
• DC–DC converter
• efficiency
• DC appliance