Page 44 - Hybrid-Renewable Energy Systems in Microgrids

28 Hybrid-Renewable Energy Systems in Microgrids

3.2 DC microgrid

A DC microgrid maintains a DC bus, which feeds DC loads connected to it. Normally,
DC loads are low-power rating electronic devices such as laptops, cell phone, wire-
less phones, DVD players, battery-powered vacuum cleaner, and Internet routers. In
DC microgrid structure, sources with DC output are connected to DC bus directly,
whereas sources with AC output are interfaced to DC bus through AC/DC converter
[8]. As the number of DC-generating renewable energy sources is higher as compared
to AC-generating sources, lesser converter units are required. This increases the over-
all efficiency of DC microgrid. In addition, the problem of harmonics due to power
electronic converter is not present due to DC nature of output power [5]. Fig. 2.3 pres-
ents the schematic diagram of a DC microgrid.
DC microgrid has advantage over AC microgrid in terms of system efficiency, cost,
and system size. Because lesser number of power electronic converters is required, the
overall efficiency improves. Additionally, AC/DC converters do not require a trans-
former, which reduces the size of DC microgrid significantly. Similar to AC microgrid,
an energy management system is required with DC microgrid as well. However, there
is only need of voltage stabilization. Compared to AC microgrid, a support for fre-
quency stabilization is not required in case of DC microgrid [9].
Sweden and Japan both have established DC microgrid structure of a capacity of
5 MW. Both of these microgrids feed DC power to data centers in their respective

Figure 2.3 DC microgrid structure.