IEEE Electrification Magazine - December 2013 - 34

90
10
0
11
0
12
0
13
0
14
0

Vcfil

0
10
20

Volts

TabLe 1. Generator fuel flow linear best-fit

200
0
-200
Time (ms)

90
10
0
11
0
12
0
13
0
14
0

30
40

IEMS
Iload

0
10
20

Amps

2
0
-2

equations.

Generator Size

Fuel Flow (gal/h)

5 kW

f5 (x) = 0.0046x + 0.113

15 kW

f15 (x) = 0.0098x + 0.2419

20 kW

f20 (x) = 0.0169x + 0.4163

Time (ms)

90
10
0
11
0
12
0
13
0
14
0

IlsA

0
10
20

Amps

2
0
-2
Time (ms)

Figure 8. The simulation results: the EMS stops providing power to
the load after it connects to VsB.

emS-Integrated Generator employment

20-kW Gen
at 7.5 kW

Power (kW)

7
6
5
4

20-kW Gen at 4.6 kW

5-kW Gen at 1.5 kW

2
20-kW Gen
at 0 kW

1
0

8 10 12 14 16 18 20 22 24
Time of Day (h)
Total
20-kW Gen Loads
5-kW Gen Loads

Fuel Flow (gal/h)

Figure 9. The traditional two-generator handling of the loads.

2.40
2.20
2.00
1.80
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00

5 kW
15 kW
20 kW

80
20
40
60
Operating Point (% of Capacity)

Figure 10. The fuel flow curves for the generators.

are given in Table 1. The generator loading, fuel flow data,
and the fuel consumed by each generator under the traditional method of employment are summarized in Table
2. Using the traditional method of generator employment
for the load profile in figure 9, the data in Table 2 show
that the two generators consumed a total of 22.7 gal of
fuel in a 24-h period.
in the next section, these results will be compared to the
scenario where an eMs manages the loads and the generators, together with a battery pack, for the same load profile.

I E E E E l e c t r i f i c ati o n M agaz ine / december 2013

100

The eMs-enabled scenario is compared to the traditional
scenario using the same 24-h load profile presented in
figure 9. Unlike the traditional scenario, the loads are connected to the eMs, not directly to a generator. Critical
loads are connected to the eMs critical bus, and the noncritical loads are connected to the eMs noncritical bus, as
shown in figure 2. figure 11 presents a notional profile
representing load demand over a 24-h period for the eMsenabled scenario.
Critical loads are those electrical devices that must be
powered at all times to ensure safety or mission success.
noncritical loads may be briefly turned off without causing
a major disruption to safety or operational requirements. To
use the same load profile for both the traditional and eMsenabled scenarios, the two sets of loads were separated into
the same groups. The loads connected to the 5- and 20-kw
generators in figure 9 correspond to the critical and noncritical loads, respectively, in figure 11.
another difference between the eMs-enabled setup
and the traditional method of generator employment is
that, in the eMs setup, no more than one generator is used
to power the loads at any given time. in other words, the
eMs may connect to generator 1, generator 2, or operate
solely on battery power.
The design principles guiding the eMs logic are as
follows:
x
provide uninterrupted power to critical loads at all
times
x
shed noncritical loads when necessary to maintain
power to the critical loads
x
use the battery bank to supplement power to maintain generator operation no higher than 100%
x
utilize the battery bank or the smallest generator possible to supply power to the loads.

Table of Contents for the Digital Edition of IEEE Electrification Magazine - December 2013