IEEE Power Electronics Magazine Compendium - March 2018 - 26

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Powering First Powering Second Powering Third
Coil Pair
Coil Pair
Coil Pair
Vehicle Stays on
Top of the
Last Coil

In-Motion Wireless Charging
Without Power Smoothing

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IEEE PowEr ElEctronIcs MagazInE

z March 2014

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Primary Coil Current Routed
by Contactors (A)

In-motion wireless charging is not a
new concept, and early investigators
sought out contactless power transfer
100
for mining vehicles and rail cars in the
50
mid-20th century. Most recently, the
0
Korean Advanced Institute for Science
-50
and Technology has made dramatic
-100
progress using buried cable concepts,
-150
similar to [45], that are excited at one
-200
end of a long hairpin-style primary over
which vehicles having polarized pickup
-250
2
3
4
5
6
7
8
coils move longitudinally [47]-[49].
Time (s)
Such systems use HF current injection
(a)
to manage the high reactive power
250
demand. The alternative, sequentially
200
Inverter Turn-Off Transition
energized coils embedded into a road150
and Coil Current Fall
way that transfer power only when the
100
vehicle secondary coil moves across
50
them, is the preferred method in the
0
ORNL system. The issue, as discussed
-50
in depth in [12], is the power pulsations
-100
on both the grid and vehicle sides; this
-150
is repeated in Figure 9, where the pulsa-200
tions are taken for the ruled position of
-250
secondary coil moving across the pri3.967
3.9675
3.968
3.9685
3.969
3.9695
3.97
Time (s)
mary coil pair. Note the exchange of the
(b)
primary real and reactive power with
250
position but the consistently leading
200
secondary reactive power. The GEM EV
150 Inverter Turn-On Transition
onboard charger is rated a1.5 kW but
and Coil Current Rise
100
also has some short-term faster charg50
ing capability. The ORNL system was
0
designed to match this charging require-50
ment while in motion. It is also appar-100
ent that circular coils exacerbate the
-150
magnitude of the power pulsation. Shift-200
ing to rectangular coils for in-motion
-250
charging would be preferable.
In ORNL's experimental testing of the
GEM EV driving over the six-coil sequenTime (s)
(c)
tially energized track, the power pulsations shown in Figure 9 are reflected in
fig 10 The grid-side HF inverter current: (a) primary current to six-coil energized
the primary coil (two coils in series, sintrack, (b) HF inverter current quenching during sequencing, and (c) HF inverter
gly tuned) current. This is shown in Figcurrent ringup during sequencing.
ure 10 as the HF inverter output current
waveform. In this compressed timescale
view, the vehicle is traversing the coils at a15 mi/h
on wireless resonant-mode power transfer has increased
resulting in three sets of double pulsation, with each
exponentially in the past three years. Much of this research
set the same as in Figure 9. The sequencing transitions
is derived from earlier fundamental work in electromagas a coil pair is dropped, and the adjacent pair is enernetics for inductive heating and cooking [34]-[38]. For
gized. This is clearly shown as the vertical dead bands.
example, ORNL's early experimental work [39]-[44] was
In this particular test run, the vehicle passes over the
prompted by investigations into alternatives to, or what
coils and then parks over the last coil to illustrate stacomes after, hybrid EVs and the need for larger batteries
tionary charging.
[45], [46].
200

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