IEEE Electrification Magazine - September 2013 - 48
there is a sudden decrease in demand in microgrid, the
frequency and voltage increases. Once the frequency or
voltage increases, the operating point may slide from A to B
with primary control to decrease the generation dispatch
and match the generation with demand. As the frequency
or voltage is above the rated value, the secondary control is
used to lower the operating point from B to C, where the
-frequency or voltage is restored to the rated values. As shown
in Figure 17, only the frequency or voltage is restored in secondary control, while the real or reactive power dispatch is
not changed. Thus, with secondary control, dispatchable
DER units would maintain the frequency and voltage at the
rated value while adjusting their dispatch according to the
tertiary control signal to serve the microgrid load. The secondary control is a centralized and performed by master
controller. The master controller will set the microgrid voltage and frequency and send the set points to primary
-control at DER level. Restoration, load sharing, and management can be performed in secondary control.
Primary Control
Figure 13. The PMU at the North Substation.
Secondary Control
Secondary control in Figure 1 is the middle level control at
the IIT microgrid. Secondary control is used to eliminate
frequency and voltage deviations caused by lower control
level (primary control). As illustrated in the Figure 17, once
The primary control, shown in Figure 1, is the lowest level
of control in the IIT microgrid. The primary control is
mainly used for load sharing among controllable and dispatchable fast-response DER units, which have adequate
capacity to serve the microgrid load. The most widely used
primary control strategy is droop control, which is shown
in Figure 18. DER units equipped with droop control, which
are connected in parallel, would not need to communicate
with each other to perform load sharing; instead, individual dispatch levels are calculated based on predefined droop
characteristics and microgrid frequency and voltage. In
PMU Information
Date
5/30/2013
Time
3:01:51 PM
ID No
Building Name
P (kW)
Q (kVAr)
Frequency
Power Factor
1
Engineering 1
590.18
832.45
60.0150
0.5784
2
Life Sciences
302.70
289.27
60.0150
0.7230
3
Stuart Building
442.60
210.45
60.0180
0.9031
4
Gunsaulus
46.28
33.48
60.0150
0.8102
5
MTCC
335.25
234.14
60.0160
0.8198
6
Hermann Hall
447.39
18.12
60.0150
0.9992
7
Wishnick Hall
426.30
200.09
60.0150
0.9052
8
Siegel Hall
138.09
260.82
60.0170
0.4679
9
North Substation
7017.33
165.26
60.0160
0.9997
10
IIT Tower
628.78
312.70
60.0120
0.8954
11
IIT Tower (20th Floor)
1238.62
537.08
60.0160
0.9175
12
Power Plant
0.00
0.00
59.9600
0.0000
Figure 14. Real and reactive power based on PMUs on DER units.
48
I E E E E l e c t r i f i c atio n Magaz ine / september 2013
Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2013
IEEE Electrification Magazine - September 2013 - Cover1
IEEE Electrification Magazine - September 2013 - Cover2
IEEE Electrification Magazine - September 2013 - 1
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IEEE Electrification Magazine - September 2013 - Cover3
IEEE Electrification Magazine - September 2013 - Cover4
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