IEEE Power Electronics Magazine - December 2014 - 21

20

15

20

15

10

5

10

5

goal of delivering conditioned power
to the end user. In this case, the cusLTC Tap at 1.0 pu
tomer is the utility, and the objective
is not only to improve the voltage at a
ENGOs OFF
250
specific end point but also to improve
245
the voltage profile across the entire
245
feeder. Conventional wisdom suggests
240
that series power electronics solutions
240
that can inject or absorb voltage [Fig235
ure 6(a)] are the best solutions to fix the
end-use voltage problems [2], [11]. How235
ever, series solutions make the voltage
230
profile worse for the rest of the feeder,
230
as they draw additional power in the
225
shunt to achieve instantaneous power
225
balance, impacting all other customers
220
7
negatively. Power losses of 2-4% of the
5:0 6:00 :00
3 4:
1:0 2:00 :00 00 a 0 a. a.m a.m
220
load kilovoltamperes appear as addi1
.
1
2
.m m. .
a
1:0 :00 0 a a.
Nodes
.
.
0 p a. .m. m. m.
tional technical losses for the utility
.m m.
y
.
of Da
and must be factored into the total cost
Time
of ownership.
(a)
A better solution may be to use
secondary-side shunt var injection, as
LTC Tap at 1.0 pu
shown in Figure 6(b), to improve the
ENGOs ON
voltage profile both locally and across
the entire feeder. Again, conventional
245
245
wisdom suggests that a high level of
reactive vars (as high as 100 kvar/V/
240
phase) may be needed to raise the
240
feeder voltage even modestly. However,
235
secondary-side shunt vars act locally
235
to offset the voltage drop across trans230
formers that are seeing high loading
230
levels or poor power factor. Analysis
DV = 7 V
225
and field data validate that significantly
lower control effort (2-3 kvar/V) may be
225
220
sufficient to correct sagging voltages at
6:0 7:00
a specific low-voltage node. Shunt vars
4 5:
2:0 3:00 :00 00 a 0 a.m a.m
220
1
:
also flow onto the primary side and
.
11: 12:0 00 0 a a.m a.m .m.
.
Nodes
.
00 0 a a.m .m
.
.
manage to improve the overall voltage
p.m .m
.
y
.
.
of Da
profile for the entire feeder. A challenge,
Time
of course, is to prevent a large number of
(b)
such shunt connected units from fighting each other.
fig 9 The impact of fleet of ENGO-V10 devices on the voltage profile of a real utility
Figure 7 shows an example of an feeder when (a) these devices are turned off and (b) when they are turned on over
LVR built around a distributed shunt two similarly loaded days.
var-injection device: the ENGO-V10
features low loss (35  W) and low weight (35 lb), and is
from Varentec. The ENGO-V10 unit is built using capacitors
designed with a long life (15 years).
controlled with smart switches for injecting varying levels
A swarm of these devices can be operated with a simple
of reactive power in the grid. The ENGO-V10 device takes
broadcast of a voltage set point, requiring no peer-to-peer
a voltage set point as an input and dynamically injects the
communication to achieve multiple control objectives at
right amount of reactive power to achieve voltage regulathe feeder level. Figure 8 shows the same feeder as Figure 3
tion. The device is rated at 0-10 kvar (single phase) and is
on a similar loading day with a substation voltage reduced
directly connected at the grid edge on the secondary side
by 3% for energy conservation but with ENGO-V10 units
of distribution transformers [12], [13]. Featuring subcycle
operating to maintain the feeder voltage at 240 V.
response, the unit corrects 2-13 V at an individual node,

December 2014

z	IEEE PowEr ElEctronIcs MagazInE

21



Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - December 2014

IEEE Power Electronics Magazine - December 2014 - Cover1
IEEE Power Electronics Magazine - December 2014 - Cover2
IEEE Power Electronics Magazine - December 2014 - 1
IEEE Power Electronics Magazine - December 2014 - 2
IEEE Power Electronics Magazine - December 2014 - 3
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