IEEE Power Electronics Magazine Compendium - March 2018 - 29

GEM Vehicle Battery Current and
Ultra-Capacitor Current (A)

Figure 17 shows the ORNL wireless charging laboratory
HF harmonics reflected to the grid have also been removed.
with the test track, GEM EV, and laboratory instrumentation;
The LiC system provides the transient energy to meet the
the ESL equipment rack is in the foreground. During this test,
power requirement of the charging coils while isolating the
the Maxwell Technologies carbon UC is in passive paralgrid from high peak power and HF harmonic content.
lel with the vehicle lead-acid battery and the ESL LiC is in
Figure 15 shows the baseline in-vehicle battery curactive parallel with the grid-side power
rent that is used as a comparator for
supply. The ESL equipment rack conthe two cases to follow for carbon
tained a dedicated power supply along
UC and LiC smoothing. These tests
with the dc-dc converter to interface
are passive parallel with the GEM
The implementation
the LiC in active parallel and designed
battery only.
of local energy storage
to mate with the ORNL trackside electronics.
Experimental Results
was shown to be very
The light poles shown in Figure 17
with Carbon UC in Vehicle
effective in reducing
on the grid-side HF current sequencIn the previous section, for an LiC in
ing electronics box and on the GEM
active parallel with the output of a
the ratio of peak-tovehicle are provided for a visual indicagrid-connected power supply, it was
average current.
tion of the grid power smoothing and
demonstrated that the active parallel
the vehicle battery pack charging curcombination of LiC energy storage
rent smoothing. Both visual indicators
and the grid supply resulted in very
showed a dramatic reduction in power
uniform power draw from the grid-
pulsation when power capacitors are used.
the power pulsations are absorbed by the LiC as expected.
This section reports on the use of Maxwell Technologies
UCs in passive parallel with the GEM lead-acid battery
Vehicle charging current smoothing Using carbon Uc
pack. The Maxwell Technologies UC module consists of a
With the equipment configured as in Figure 16, for in-vehicle
single string of 30 # 650 F, 2.7 V/cell for a combined 21.7 F
instrumentation and with a pair of power analyzers-one
at 81 V pack, shown in Figure 16, capable of 52 kJ (14.4
monitoring the grid side and the second installed in the
Wh) if discharged from maximum to half-rated voltage.
The carbon UC pack (30 S # 1 P # 650 F) shown in Figure
16 was precharged to match the GEM battery pack voltage
15
UC Current
prior to installation. This was necessary to avoid any cur10
GEM Battery Current
rent surges between the UC pack, GEM battery, and WPT
secondary-side filter capacitors during connection. The
5
UC pack was then installed in the GEM and connected to
0
the battery, as shown in Figure 16. In addition, a Yokagawa
-5
power meter and isolation modules were installed in the
vehicle to record currents and voltages, at the UC and to
-10
the battery pack.
-15
-20

5
4
Time (s)

fig 18 The in-vehicle UC and battery currents (peak UC current
a13.4 A and peak battery current a2.6 A).

fig 17 In-motion wireless charging is tested at ORNL using
electrochemical capacitor smoothing. (Cliff White is monitoring
the grid-side equipment, and Steven Campbell is driving
the test vehicle.) (Photo courtesy of ORNL.)

Table 1. A summary of the
current pulsation reduction.

Experimental test

grid-side wPt
Base station

No smoothing
Grid side only with LiC
Vehicle side with UC
Vehicle side with LiC

53 A
10 A
10 A
10 A

Pulse reduction

81%

March 2014

In-Vehicle
16 A
16 A
2.6
2.6
84% for UC
84% for LiC

z IEEE PowEr ElEctronIcs MagazInE

Table of Contents for the Digital Edition of IEEE Power Electronics Magazine Compendium - March 2018