Page 434 - Decision Making Applications in Modern Power Systems

394 Decision Making Applications in Modern Power Systems

Therefore it required large size of PV plant and BB to provide the uninter-
rupted power supply, which is the cause of highest capital cost.
In the case of DC distribution system including DC appliances (DCDSD)
the high-efficient appliances are used as well as the conversion staged at the
source as well as load end has been removed [15,16]. Therefore the energy
demand for DCDSD is smaller as compared to ACDSA and AC distribution
system including DC appliances. The small size of PV plant and the BB is
sufficient with DCDSD. In the case of DCDSD DSM the DSM scheme
shifts the operating time of the deferrable appliances that help to reduce the
charging and discharging of the BB and save the energy loss in the BB. In
this way, there is a further improvement in the system efficiency. Therefore
a small amount of AH and PV Watt-hours per day is needed, which is the
cause of less numbness (i.e., size of ES) of the battery and PV modules to
supply the uninterrupted power supply to the building. The capital cost of
the DCDSD DSM system is the smallest in comparison to other three cases
because it depends on the size of PV plant and BB.

15.3 State of charge of battery bank
In general the SOC of the battery is the ratio of its present capacity (μ(t)) to
the nominal capacity (μ n ) of the battery [17]. The SOC can be defined as
μðtÞ
ψðtÞ 5 ð15:6Þ
μ n
The Coulomb counting method measures the charging/discharging current
of a battery and integrates it over time in order to estimate SOC [16,17]. The
SOC can be calculated as
iðtÞ
ψðtÞ 5 ψðt 2 1Þ 1 Δt ð15:7Þ
μ n
where ψ(t) and ψ(t 2 1) are the SOC of the battery at time instant t and
t 2 1, i(t) is the battery current at time instant t, and Δt is the time interval
(considered 1 minute).

15.4 Autonomous DC microgrid

The conceptual diagram, hardware of the experimental setup, and control
and monitoring unit of the DC microgrid for the building are discussed in
this section.

15.4.1 Conceptual diagram of DC microgrid

The conceptual layout of the prototype autonomous DC microgrid of the res-
idential building is shown in Fig. 15.1. Two solar charge controllers (SCCs)