IEEE Electrification Magazine - March 2015 - 65

Table 6. The Integrated energy-Storage System Solution.
Item

St. Thomas Installation

St. Croix Installation

Power Electronics

S&C PureWave SMS
1.25 MVA/1.0 MW

S&C PureWave SMS-250
263 kVA/250 kW

Battery

Lithium-ion 3,000 kWh or
sodium-nickel-chloride (NaNiCl) 2,400 kWh (Total of 3,000-kWh
embedded energy, but limited to 80% depth of discharge)

Lithium-ion
2,000 kWh

from the battery and create the fixed dc link voltage for the
inverter system. The SMS controls the chopper circuits to
allow charging or discharging of the batteries within the rigorous requirements provided by the battery manufacturer. The
choppers are controlled to determine the direction of power
flow and are current-limited by the controls in accordance
with the battery controller's commands.
The digital signal processing-based SMS controls provide efficient operation across a wide range of power levels, which is a benefit for variable-power applications, as
shown in Figure 12. All of the SMS subsystems are housed
in a custom enclosure mounted inside an ISO container. A
typical SMS ISO container without the transformer and
batteries is shown in Figure 13.

Battery
The world of energy-storage choices can be complicated.
Each energy-storage technology presents its own set of pros/
cons, maturity level, and costs. Table 7 provides a summary
the different technologies available today. Based on the project requirements, a lithium-ion battery system has been considered for the St. Croix site, and options of both the lithiumion battery system and a sodium-nickel-chloride (NaNiCl)
battery system were considered for the St. Thomas site. Lithium-ion batteries, with their combination of high discharge
rates, excellent energy density, modularity, and low

Charge (kW)

courtesy of S&C Electric, "Storage Management System," http://
sandc.com/products/energy-storage/sms.asp.)

SMS Efficiency

Possible
Combinations of
Real and Reactive
Power
Efficiency (%)

Inductive (kvar)

Figure 11. The ±1.25-MVA SMS inverter and two choppers. (Image

Discharge (kW)

Capacitive (kvar)
Figure 10. A conceptual four-quadranat power-conversion system.
(Image courtesy of S&C Electric, "Storage Management System,"
http://sandc.com/products/energy-storage/sms.asp.)

100
90
80
70
60
50
40
30
20
10
0

0

10 20

30

40 50 60
Power (%)

70

80

90 100

Figure 12. An SMS efficiency curve. (Image courtesy of S&C Electric,
"Storage Management System," http://sandc.com/products/energystorage/sms.asp.)

	

IEEE Electrific ation Magazine / March 2 0 1 5

65


http://http:// http://www.sandc.com/products/energy-storage/sms.asp http://www.sandc.com/products/energy http://www.sandc.com/products/energy-storage/sms.asp

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