A Study on DC Microgrids Voltages based on Photovoltaic and Fuel Cell Power Generators

DC microgrid based on photovoltaic (PV, 500 WP) and fuel cell (FC, 1 kW) power generators have been designed to operate DC loads at different voltage levels (24 V, 48 V and 110 V). The voltage level in a DC microgrid decides the system efficiency, voltage regulation and the total cost. The system efficiency is shown to depend on the power conversion mode (DCDC converter) efficiency and ohmic loss (in connecting cables). DC loads used vary from 250 W to 1000 W and according the cable sizing is required to be changed to improve the voltage regulation and to reduce the cable loss. The buck-boost DC-DC converter is used in 24/48 V microgrids, while boost converter is required for 110 V microgrid. The buck-boost converter efficiency is $\approx$ 85% and the boost converter provides efficiency $\approx$ 95%. It is shown that 110 V DC voltage level gives optimum performance for low power DC microgrid in comparison with 24 V or 48 V.