IEEE Power Electronics Magazine - December 2014 - 19

Substation Voltage on 240-V Base
Secondary Voltage at 24 Locations
LTC Tap at 1.0 pu

ANSI Low Limit
250

245

245

240

240
Voltage

250

235
230

235
230

p.
m
12
.
:0
0
a.
m
.
1:
00
a.
m
.
2:
00
a.
m
.
3:
00
a.
m
.
4:
00
a.
m
.
5:
00
a.
m
.
6:
00
a.
m
.

11
:0
0

.
a.
m

a.
m

6:
00

5:
00

a.
m

4:
00

a.
m

3:
00

a.
m

a.
m

2:
00

a.
m

1:
00

12
:0
0

p.
m
11
:0
0

.

215

.

215

.

220

.

220

.

225

.

225

.

Voltage

LTC Tap at 1.035 pu

Time of Day

Time of Day

(a)

(b)

fig 3 (a) With the LTC tap at 1.035 pu, infrequent ANSI violations are observed. (b) With the LTC tap taken down to 1.0 pu, more
than half of the 24 monitored locations have a persistent low-voltage issue.

single-phase loads and could
Primary Distribution Network
be rated higher for three- LTC, Capacitor Bank, LVR, End of Line
phase loads, giving an idea of
V
Sensor, etc.
the rating for the power converter needed. However,
Supervisory
these transformers can operControl and
ate at 150% loading for exData
Service Transformer
tended periods of time and
Acquisition
will source thousands of amperes of fault current for
downstream faults, which the
converters will need to manGrid-Edge
Secondary-Side Assets
age. The transformers isolate
Controllers
Provide Control at the Grid
Meter
the converter from the 100-kV
Head End
Edge
BIL rating, but normal lightning-strike protection is still
Rooftop Solar PV
required. To ensure reliability,
the converter must operate in
fig 4 A distribution feeder single-line schematic showing where distributed grid-edge controla fail-normal mode, ensuring lers could be used.
that service to the load is not
interrupted in case of a converter failure. Outdoor installation near the transformer
Dual-Active
also suggests that the unit must be able to operate over an
Bridge
ambient temperature range of -40 cC to +55 cC with no
planned service or maintenance over the life of the converter. This suggests the use of passive thermal management
MVAC
MVDC
LVDC
LVAC
and poses severe challenges for the size, weight, and cost
of the required power converters. The installation and comfig 5 An example of a single- or three-phase SST with a rectifimissioning should be achieved without service interruption
er stage, followed by a high-frequency galvanically isolated dc-
for the customers. Furthermore, diagnostics and communidc step-down or step-up conversion stage, typically realized
cations are critical to manage a fleet of distributed assets.
with a dual-active bridge, and an inverter stage.
December 2014

z	IEEE PowEr ElEctronIcs MagazInE

19



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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IEEE Power Electronics Magazine - December 2014 - 11
IEEE Power Electronics Magazine - December 2014 - 12
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IEEE Power Electronics Magazine - December 2014 - Cover3
IEEE Power Electronics Magazine - December 2014 - Cover4
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