Page 39 - From Smart Grid to Internet of Energy

28 From smart grid to internet of energy

FIG. 1.10 Block diagram of a microgrid architecture [20].

synchronized interval. This operation is called island detection and resynchro-
nization process [21]. The centralized microgrid control includes hierarchical
control levels that are performed by interaction of MGCC with source control-
lers (SC) and load controllers (LC) as shown in Fig. 1.10. The hierarchical con-
trol of microgrid is generally performed in three levels regarding to SC and LCs,
centralized MGCC control, and distribution management system at the last
level. The hierarchical control optimizes efficiency and reliability of microgrid
by preventing curtailments and blackouts. In addition, it is noted that MGCC
can provide around 22% savings for daily operation in high price regime,
and 2% decrement on operation and maintenance cost per year [21].
The MGCC is utilized to interface microgrid and distribution management
system (DMS) which is used to detect blackouts and other fault types during the
operation of utility grid. The MGCCs are featured as AC and DC central con-
trollers depending to microgrid types that will be used. In an AC microgrid the
load and sources operate in AC waveforms and thus the DERs should be con-
nected to microgrid by inverters. In addition to voltage and frequency control
performed by power inverters, several featured power controllers such as uni-
fied power quality conditioners (UPQCs) and P-Q controllers are required in
AC microgrid and MGCC. Therefore, the hierarchical control scheme of AC
microgrid is more complicated and more sophisticated controllers are required
to ensure appropriate connection to utility grid. on the other hand, DC microgrid
is operated much more easily comparing to AC microgrid since it does not
require frequency and phase control. Since the most of RESs as well as ESSs