IEEE Electrification Magazine - December 2013 - 26

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Figure 6. The block diagram of the storage inverter controls.

and energy density of the device. Nca has high energy and
power densities and an excellent life span, whereas NMc
presents lower power density with almost similar energy
density but represents better safety features. the development of lithium iron phosphate (lifePo4) in the 1990s for
positive active materials was a significant safety improvement. However, lower energy and power density and cell
voltage were the drawbacks of this type of battery cell.
since the 1980s, when rachid Yazami proposed graphite as the negative active material in secondary

(rechargeable) li-ion batteries, it has
been commonly used because of the
reversible electrochemical intercalation (insertion) of lithium ions.
graphite as a negative electrode is
sensitive to the operating temperature of the cell. by overheating the
Data
battery cell, the li-ion permeable
Comm
Bus
solid-electrolyte interphase layer
protecting lithium ions from reacting with electrolyte breaks down,
and an irreversible reaction between
the lithium ions and electrolyte may
cause thermal runaway and, potentially, fire. replacing the graphite
V
with lithium titanate as the negative
I
active material eliminates the overheating issue. Moreover, because of
the capability of lithium titanate to
operate at higher voltages, a higher
LCL
charging rate is possible, which
Filter
reduces the charging time to as low
as several minutes. on the other
hand, the power and energy density
as well as the cell terminal voltage
are reduced. the electrolyte in li-ion
batteries is normally a lithium-salt
such as lithium hexafluorophosphate in an organic solvent.
figure 4 shows a comparison of
several types of battery chemistries,
considering lithium iron phosphate
as a reference case. an appropriate type can be chosen
based on the requirements for energy and power density,
cost, cycle life, performance, and safety.

Optimal Allocation for
eSS in microgrids

60
480

Planning the best locations and sizes for esss can have a
significant impact on the power system, including
enhancing the power system reliability and power quality,
reducing the power system cost, controlling high energy
cost imbalance charges, minimizing
power loss, improving voltage profiles, serving the demand for peak
load, and correcting the power factor.
Frequency
in recent years, much research
has been focused on determining the
location and capacity of esss. algorithms combining multipass dynamic programming were proposed to
Voltage
Storage Power
maximize fuel-cost savings and benefits from energy pricing differences
1′ 10″
1′ 00″
0′ 50″
0′ 40″
0′ 30″
0′ 20″
0′ 10″
0′ 00″
between peak- and light-load periods. Methodologies were also develFigure 7. The microgrid voltage, frequency, and output power of a storage inverter in black start
oped to optimize the allocation and
and island mode.

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

http://www.shf.pf http://www.shf.pf

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