Page 442 - Decision Making Applications in Modern Power Systems

Impact of demand-side management system Chapter | 15 401

In case the surplus PV power is less than the building demand while the
difference of desired time (t d ) to complete its task and appliance “ON” time
(t r ) is greater than or equal to the difference of task completion time instant
(t tc ) and decision time instant (t di ) then the deferrable load is switched “ON,”
while the refrigerator operates with “control cycle” and other noncritical
loads get switched “OFF.” The priority of the deferrable load is based on the
desired “ON” time of the loads to complete the task. For example, at 10:00
hours time instant the PV plants produce approximately 90 W of the surplus
power, which activates the controller to switch “ON” the deferrable load up
to 90 W, while the status of the deferrable loads is as follows: the washing
machine (70 W) should run for 90 minutes up to 13:00 hours to wash the
cloth as per the consumer desires (instructions), and pump (80 W) must run
for 30 minutes to 10:50 hours. The differences of the decision time instant
and task termination time instants are 180 and 50 minutes for washing
machine and pump, respectively. It verifies that the pump has more priority
than the washing machine; therefore pump gets switched “ON,” and washing
machine remains switched “OFF.”
When the PV power generation is greater than the building demand (i.e.,
demand of critical and noncritical loads, including deferrable loads) and the deci-
sion time instant belongs to the task slot of the deferrable load while its task is
not completed, the deferrable load remains switched “ON,” and the surplus PV
power feeds to the battery. On the other hand, if the decision instant does not
belong to the task slot of the deferrable load, then it remains switched “OFF.”

15.6 Results and discussions
The actual hardware setup of an autonomous DC microgrid has been built to
validate the feasibility of the DSM scheme for the building. The PV plant, ES,
and DC appliances are connected to the unipolar DC bus based distribution
system. The two SCCs are connected in parallel to connect the array-1 and
array-2 of the PV plant with the load and ES. Each SCC has three terminals to
connect with the PV plant, ES, and load. The BB terminals of both the SCCs
are connected to each other via 12 V DC bus. This type of connection between
BB terminals of SCCs connects the batteries in parallel and provides the com-
mon point of connection to both the SCCs to connect with the ES. The beauty
of these connections is that the ES can store the surplus power of both the
SCCs and supply their surplus demand. The DC bus power can be expressed as

n a n pv n b
X X X
P aj ðtÞ 5 P pvj ðtÞ 6 P bbj ðtÞ ð15:8Þ
j51 j51 j51
where P bbj is the power of jth battery, n b is the number of batteries, P pvj is
the power of jth PV array, n pv is the number of PV arrays, P aj is the power
consumption in jth appliance, and n a is the number of appliances.