IEEE Power Electronics Magazine Compendium - March 2018 - 28

dc Power Supply Current
with Li-Ion Support (A)
dc Power Supply Current
without Li-Ion Capacitor (A)

20

Supply Bus

LiC
Charging

15

Similarly, the rectified load current can be approximated
as the ac equivalent, I r of dc load current into the battery
pack according to (4). The primary line current in resonance
is then the vector sum of real and quadrature currents (5).

LiC
Charging

10

r P0
2 2 Ud
2, 000
= 1.11 80 = 27.8 A rms

5

Ir =
Grid-Side
Supply Current

0
-5

0

1

2

3
4
Time(s)
(a)

5

6

7

I pri = I 2m + I 2r
= (- 98.88) 2 + 27.8 2
= 102.8 A rms .

50

HF Inverter
40
Input Current
30
10

Experimental Results with LiC on the Primary Side

0
0

1

2

3
4
Time(s)
(b)

5

6

7

GEM Vehicle Lead-Acid Battery
Current Without Energy Buffer (A)

fig 14 The grid-side currents with active parallel LiC system:
(a) the grid-side supply current (13 A) and (b) the current delivered to the HF inverter.

20

Battery Charge
from Coils

15
10
5
0
-5

Battery
Discharge
for Traction

-10
-15
-20

0

1

2

3

5
4
Time(s)

6

7

8

fig 15 The in-vehicle battery-only current (16 A peak ).

(a)

(b)

fig 16 The in-vehicle UC installation: (a) the ultracapacitor pack
during precharging operation and (b) the charged ultracapacitor
pack installed in GEM and connected in passive parallel with battery. (Photos courtesy of ORNL.)

28

(5)

This is consistent with the current magnitudes shown
in Figure 10, where (5) is equivalent to 145 A peak .

20

-10

(4)

IEEE PowEr ElEctronIcs MagazInE

z	March 2014

The main body of testing done at ORNL involved highpower capacitors. ESL fabricated the LiC equipment rack
shown in Figure 11 that contains components for three individual tests: 1) a standalone LiC consisting of four 40-V
modules in series for grid-side passive parallel; 2) an LiC
plus dc-dc converter for active parallel demonstration on
the grid side; and 3) a pair of 40-V LiC modules for in-vehicle
installation and comparison with carbon UC in passive parallel with the GEM battery.
Figure 12 shows a block diagram of the active parallel
converter system used only on the grid side. It consists of
a multiphase bidirectional half-bridge dc-dc converter, an
LiC module, and a controller. The dc-dc converter matches
the voltage and current levels of the LiC module with the
requirements of the wireless charger bus. The specifications
of the LiC module depend upon the acceptable charging
power level from the grid and the pulse duration and duty
cycle of the power required by the wireless charger. During
high-power transients, such as when a vehicle drives over
the charging coils, the controller uses the dc-dc converter
to transfer energy out of the LiCs to load level the grid-side
ac-dc converter bus. Otherwise, the converter is used to
recharge the capacitor bank. Figures 13 and 14 show the benefits of using this system.
Figure 13(a) shows the grid-side LiC voltage as the GEM
vehicle drives over the charging coils with the grid-side
LiC passive parallel system enabled. Figure 13(b) shows
the grid-side LiC current during this same event. Large pulsations would be present. However, here, the LiC supplies
the transient currents. Notice that the magnitude of the
LiC current is larger than the inverter current because the
LiC stack is at a lower voltage than the bus, and the dc-dc
converter matches the LiC output power to the required
inverter power.
Figure 14 shows the grid supply and HF inverter currents when the grid-side active parallel system is enabled.
The large peak current pulse on the grid side has been eliminated and replaced by a regulated and leveled current load
needed to recharge the LiC system. Moreover, most of the
Table of Contents for the Digital Edition of IEEE Power Electronics Magazine Compendium - March 2018
