IEEE Electrification Magazine - December 2013 - 57

Grid

L1
L2
L3

Cdc1

S5
Cdc

dc/dc
Converter

Grid

dc/dc
Converter

L2
L3

Vbat
-

(a)

+
V
- bat

Cdc2

(b)

Figure 15. Level 3 chargers using (a) a six-switch boost rectifier and (b) a Vienna rectifier.

the total system losses. advanced power devices,
including wide-band-gap silicon carbide and gallium
nitride semiconductor devices with low on resistances, high voltage ratings, faster switching speeds, and
high operating temperatures, help reduce the power
losses and the thermal stress.
5) Advanced converter topologies and control methods:
the converter topology determines the circuit performances such as the ZVS feature, eMi, circulating current, conduction losses, and switching losses. an
optimized circuit topology and
control method would help optimize the overall circuit performance over the wide battery Soc
range.

Off-board charging

equipped with an active front-end rectifier (in the ac/dc
stage) can mitigate this problem, it increases the cost of the
charging station substantially. alternatively, the degradation
of distribution equipment can be reduced by employing a
smart charging strategy. the allowable harmonic and dc
injection into the grid are limited by ieee 1547, Sae-J2894
iec1000-3-2, and the U.S. national electric code (nec) 690
standards.
Different topologies are reported for three-phase offboard chargers. Since the level 3 battery charger is typically supplied by 480-V three-phase
voltage, the grid voltage would be
higher than the battery voltage. as
mentioned earlier, an active pFc rectifier is required to alleviate grid power
quality issues. hence, a three-phase
boost converter followed by a dc/dc
converter is required to charge the
battery. additionally, as mentioned in
the "isolated onboard peV chargers"
section, the galvanic isolation is
important in the charger circuits for
safety reasons. even though peV
charging standards do not mandate
galvanic isolation as long as the
ground current is maintained within limited boundaries, if
the battery is attached to the vehicle's chassis, galvanic
isolation is mandatory for safety reasons. therefore, to
avoid costly and complex shielding considerations for a
nonisolated dc/dc converter, an isolated dc/dc converter is
preferred. Similar to oBcs, as shown in Figure 9, the resonant converters are the preferred topologies for the second conversion stage of off-board charging because of
their improved efficiencies.
the three-phase six-switch boost and Vienna converters are the most suitable topologies for level 3 charger
applications. Figure 15(a) shows the schematic of a common three-phase boost-type voltage-source converter
(VSc) followed by a resonant dc/dc converter. the VSc has
a relatively simple structure, despite its high functionality,
that includes six semiconductor switches, three input
inductors, and one output filter capacitor to provide input
pFc and output voltage regulation simultaneously. in this

Charging
convenience and
charging time are
two of the most
important concerns
from the consumer
perspective.

Level 3 charging, known as dc fast
charging, requires an off-board
charger, which is less constrained by
size. Fast charge, rapid charge, and
quick charge are a few of the
commonly used terms for off-board,
as shown in table 4. the high power
level and high cost of off-board
charging make it unfeasible for residential areas. Level 3
charging is not compatible with commercial and residential outlets and, consequently, requires the installment of
new charging infrastructure. nonetheless, it is attractive
for commercial and public applications such as shopping
centers, parking lots, hotels, highway rest areas, and
ordinary filling stations.
as shown in Figure 14, a level 3 charger is typically fed
through a 208-600-Vac three-phase circuit. this system consists of an ac/dc stage and a dc/dc stage. Because of the high
current/power requirements, the off-board charging puts
power quality burdens on electric utility distribution systems. these burdens can include voltage deviations, harmonic distortion, peak demand, and thermal loading on
distribution power systems. in particular, the harmonic and
dc injection can particularly increase distribution transformer losses resulting in thermal loading, which impacts transformer aging accordingly. although a charging system

IEEE Electrific ation Magazine / d ec em be r 2 0 1 3

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