IEEE Electrification Magazine - September 2013 - 63

Currently available
energy-storage
devices, with lithiumion (Li-ion) batteries
being the most
promising, need
substantial
performance
improvements to
effectively compete
with petroleum.

chargers, with multiple receiver pads
used for higher-power applications.
For example, KAIST's second-generation IPT-supplied bus carries ten
6-kW pickups. On the source side,
however, the lumped coil used for
stationary wireless chargers is
replaced with an elongated conductive cable buried in the road. Some
implementations, including the ones
mentioned earlier, make use of ferromagnetic material at the primary to
direct the magnetic flux, reduce magnetic reluctance, and minimize the
field emissions when the receiver coil
does not couple with a section of the
source coil.
Although the systems using single-coil designs achieve acceptable
efficiency, peaking at around 70%,
there is still substantial room for improvement, given that
stationary chargers attain 90% efficiency. Because of an
increased misalignment during dynamic charging, it is
reasonable to expect lower system-level efficiency compared to stationary applications. In theory, the efficiency

Dynamic Charging System Implementation
60

Area Covered with ICPT
(ICPT Power: 40 kW, Drive Cycle: UDDS)

14,000
12,000

10,000

Explorer
Speed (mi/h)

As described earlier, a dynamic charging system consists
of a source coil embedded in the road, and a receiver system attached to the vehicle chassis. As a result of the vehicle movement, the receiver of a dynamic charging system
moves laterally and longitudinally in a plane parallel to
the source coil. The source coil designs can be categorized
as single-coil designs, where the source coil is substantially
larger than the receiver, or segmented coil designs where
the source is made of multiple lumped coils that are commeasurable in size with the receiving coil.
Considering the single-coil designs, an obvious advantage is a reduction in system complexity due to the simplified system control, reduced number of converters, and
relatively constant coupling between the source and the
receiver. The demerits of the approach are that 1) the
resulting coupling coefficient between the source and
the receiver is relatively low because of the large uncoupled flux of the source coil; 2) field emissions in the
uncoupled sections of the coil need to be contained to
ensure safety; and 3) the large inductance of the coil for
which the distributed capacitors must compensate to
limit the voltage at the coil terminals.
Because of their simplicity, single-coil designs are quite
popular in practical implementations of dynamic charging
systems, as evidenced in the systems developed by
researchers at Bombardier and KAIST. An example of the
elongated track is illustrated in Figure 7. The receiver system
in this application is similar to the one used in stationary

40
Impala
Insight

8,000
6,000
4,000

2,000
10
0

0
0

200

400

Distance (m), ICPT Track Area

the results of the third row of Table
2, depicting the IPT coverage
required on the UDDS drive cycle.
Figure 6 shows the velocity versus
time plot of the UDDS on the left
y-axis. On the right y-axis, the distance versus time plot is shown for
the same driving cycle, for the three
vehicles of interest. The three plots
are offset from each other for clearer viewing. The black lines on the
distance versus time plot signify the
sections of the driving cycle that
were chosen (using an optimization
routine) as optimal sites for installing the dynamic charging system.
The power transfer to the vehicle is
considered to be 30 kW. The results
of this simplified study show promising results: if only 1% of the roadway is powered in urban environments, most vehicle
types can easily meet the 300-m target range with the relatively small battery pack described earlier. The assumptions and details of the study can be found in [1], along
with other interesting results that, for brevity, are not
repeated here.

-2,000
600 800 1,000 1,200 1,400
Time (s)

Figure 6. The area covered with IPT-optimization for different cars.
(Reproduced from [1].)

Vehicle
Receiver
Magnetic Core
Coil
Roadway
Primary Coil

Primary Core

Figure 7. An illustration of the dynamic charging concept.
IEEE Elec trific ation Magazine / s ep t em be r 2 0 1 3

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